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diff --git a/doc/draft-ietf-secsh-filexfer-02.txt b/doc/draft-ietf-secsh-filexfer-02.txt deleted file mode 100644 index 45e979e..0000000 --- a/doc/draft-ietf-secsh-filexfer-02.txt +++ /dev/null @@ -1,1626 +0,0 @@ - - -Network Working Group T. Ylonen -Internet-Draft S. Lehtinen -Expires: April 1, 2002 SSH Communications Security Corp - October 2001 - - - SSH File Transfer Protocol - draft-ietf-secsh-filexfer-02.txt - -Status of this Memo - - This document is an Internet-Draft and is in full conformance with - all provisions of Section 10 of RFC2026. - - Internet-Drafts are working documents of the Internet Engineering - Task Force (IETF), its areas, and its working groups. Note that - other groups may also distribute working documents as Internet- - Drafts. - - Internet-Drafts are draft documents valid for a maximum of six months - and may be updated, replaced, or obsoleted by other documents at any - time. It is inappropriate to use Internet-Drafts as reference - material or to cite them other than as "work in progress." - - The list of current Internet-Drafts can be accessed at http:// - www.ietf.org/ietf/1id-abstracts.txt. - - The list of Internet-Draft Shadow Directories can be accessed at - http://www.ietf.org/shadow.html. - - This Internet-Draft will expire on April 1, 2002. - -Copyright Notice - - Copyright (C) The Internet Society (2001). All Rights Reserved. - -Abstract - - The SSH File Transfer Protocol provides secure file transfer - functionality over any reliable data stream. It is the standard file - transfer protocol for use with the SSH2 protocol. This document - describes the file transfer protocol and its interface to the SSH2 - protocol suite. - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 1] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -Table of Contents - - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 - 2. Use with the SSH Connection Protocol . . . . . . . . . . . . 4 - 3. General Packet Format . . . . . . . . . . . . . . . . . . . 5 - 4. Protocol Initialization . . . . . . . . . . . . . . . . . . 7 - 5. File Attributes . . . . . . . . . . . . . . . . . . . . . . 8 - 6. Requests From the Client to the Server . . . . . . . . . . . 10 - 6.1 Request Synchronization and Reordering . . . . . . . . . . . 10 - 6.2 File Names . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 6.3 Opening, Creating, and Closing Files . . . . . . . . . . . . 11 - 6.4 Reading and Writing . . . . . . . . . . . . . . . . . . . . 13 - 6.5 Removing and Renaming Files . . . . . . . . . . . . . . . . 14 - 6.6 Creating and Deleting Directories . . . . . . . . . . . . . 15 - 6.7 Scanning Directories . . . . . . . . . . . . . . . . . . . . 15 - 6.8 Retrieving File Attributes . . . . . . . . . . . . . . . . . 16 - 6.9 Setting File Attributes . . . . . . . . . . . . . . . . . . 17 - 6.10 Dealing with Symbolic links . . . . . . . . . . . . . . . . 18 - 6.11 Canonicalizing the Server-Side Path Name . . . . . . . . . . 18 - 7. Responses from the Server to the Client . . . . . . . . . . 20 - 8. Vendor-Specific Extensions . . . . . . . . . . . . . . . . . 24 - 9. Security Considerations . . . . . . . . . . . . . . . . . . 25 - 10. Changes from previous protocol versions . . . . . . . . . . 26 - 10.1 Changes between versions 3 and 2 . . . . . . . . . . . . . . 26 - 10.2 Changes between versions 2 and 1 . . . . . . . . . . . . . . 26 - 10.3 Changes between versions 1 and 0 . . . . . . . . . . . . . . 26 - 11. Trademark Issues . . . . . . . . . . . . . . . . . . . . . . 27 - References . . . . . . . . . . . . . . . . . . . . . . . . . 28 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 28 - Full Copyright Statement . . . . . . . . . . . . . . . . . . 29 - - - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 2] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -1. Introduction - - This protocol provides secure file transfer (and more generally file - system access) functionality over a reliable data stream, such as a - channel in the SSH2 protocol [3]. - - This protocol is designed so that it could be used to implement a - secure remote file system service, as well as a secure file transfer - service. - - This protocol assumes that it runs over a secure channel, and that - the server has already authenticated the user at the client end, and - that the identity of the client user is externally available to the - server implementation. - - In general, this protocol follows a simple request-response model. - Each request and response contains a sequence number and multiple - requests may be pending simultaneously. There are a relatively large - number of different request messages, but a small number of possible - response messages. Each request has one or more response messages - that may be returned in result (e.g., a read either returns data or - reports error status). - - The packet format descriptions in this specification follow the - notation presented in the secsh architecture draft.[3]. - - Even though this protocol is described in the context of the SSH2 - protocol, this protocol is general and independent of the rest of the - SSH2 protocol suite. It could be used in a number of different - applications, such as secure file transfer over TLS RFC 2246 [1] and - transfer of management information in VPN applications. - - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 3] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -2. Use with the SSH Connection Protocol - - When used with the SSH2 Protocol suite, this protocol is intended to - be used from the SSH Connection Protocol [5] as a subsystem, as - described in section ``Starting a Shell or a Command''. The - subsystem name used with this protocol is "sftp". - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 4] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -3. General Packet Format - - All packets transmitted over the secure connection are of the - following format: - - uint32 length - byte type - byte[length - 1] data payload - - That is, they are just data preceded by 32-bit length and 8-bit type - fields. The `length' is the length of the data area, and does not - include the `length' field itself. The format and interpretation of - the data area depends on the packet type. - - All packet descriptions below only specify the packet type and the - data that goes into the data field. Thus, they should be prefixed by - the `length' and `type' fields. - - The maximum size of a packet is in practice determined by the client - (the maximum size of read or write requests that it sends, plus a few - bytes of packet overhead). All servers SHOULD support packets of at - least 34000 bytes (where the packet size refers to the full length, - including the header above). This should allow for reads and writes - of at most 32768 bytes. - - There is no limit on the number of outstanding (non-acknowledged) - requests that the client may send to the server. In practice this is - limited by the buffering available on the data stream and the queuing - performed by the server. If the server's queues are full, it should - not read any more data from the stream, and flow control will prevent - the client from sending more requests. Note, however, that while - there is no restriction on the protocol level, the client's API may - provide a limit in order to prevent infinite queuing of outgoing - requests at the client. - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 5] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - The following values are defined for packet types. - - #define SSH_FXP_INIT 1 - #define SSH_FXP_VERSION 2 - #define SSH_FXP_OPEN 3 - #define SSH_FXP_CLOSE 4 - #define SSH_FXP_READ 5 - #define SSH_FXP_WRITE 6 - #define SSH_FXP_LSTAT 7 - #define SSH_FXP_FSTAT 8 - #define SSH_FXP_SETSTAT 9 - #define SSH_FXP_FSETSTAT 10 - #define SSH_FXP_OPENDIR 11 - #define SSH_FXP_READDIR 12 - #define SSH_FXP_REMOVE 13 - #define SSH_FXP_MKDIR 14 - #define SSH_FXP_RMDIR 15 - #define SSH_FXP_REALPATH 16 - #define SSH_FXP_STAT 17 - #define SSH_FXP_RENAME 18 - #define SSH_FXP_READLINK 19 - #define SSH_FXP_SYMLINK 20 - #define SSH_FXP_STATUS 101 - #define SSH_FXP_HANDLE 102 - #define SSH_FXP_DATA 103 - #define SSH_FXP_NAME 104 - #define SSH_FXP_ATTRS 105 - #define SSH_FXP_EXTENDED 200 - #define SSH_FXP_EXTENDED_REPLY 201 - - Additional packet types should only be defined if the protocol - version number (see Section ``Protocol Initialization'') is - incremented, and their use MUST be negotiated using the version - number. However, the SSH_FXP_EXTENDED and SSH_FXP_EXTENDED_REPLY - packets can be used to implement vendor-specific extensions. See - Section ``Vendor-Specific-Extensions'' for more details. - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 6] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -4. Protocol Initialization - - When the file transfer protocol starts, it first sends a SSH_FXP_INIT - (including its version number) packet to the server. The server - responds with a SSH_FXP_VERSION packet, supplying the lowest of its - own and the client's version number. Both parties should from then - on adhere to particular version of the protocol. - - The SSH_FXP_INIT packet (from client to server) has the following - data: - - uint32 version - <extension data> - - The SSH_FXP_VERSION packet (from server to client) has the following - data: - - uint32 version - <extension data> - - The version number of the protocol specified in this document is 3. - The version number should be incremented for each incompatible - revision of this protocol. - - The extension data in the above packets may be empty, or may be a - sequence of - - string extension_name - string extension_data - - pairs (both strings MUST always be present if one is, but the - `extension_data' string may be of zero length). If present, these - strings indicate extensions to the baseline protocol. The - `extension_name' field(s) identify the name of the extension. The - name should be of the form "name@domain", where the domain is the DNS - domain name of the organization defining the extension. Additional - names that are not of this format may be defined later by the IETF. - Implementations MUST silently ignore any extensions whose name they - do not recognize. - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 7] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -5. File Attributes - - A new compound data type is defined for encoding file attributes. It - is basically just a combination of elementary types, but is defined - once because of the non-trivial description of the fields and to - ensure maintainability. - - The same encoding is used both when returning file attributes from - the server and when sending file attributes to the server. When - sending it to the server, the flags field specifies which attributes - are included, and the server will use default values for the - remaining attributes (or will not modify the values of remaining - attributes). When receiving attributes from the server, the flags - specify which attributes are included in the returned data. The - server normally returns all attributes it knows about. - - uint32 flags - uint64 size present only if flag SSH_FILEXFER_ATTR_SIZE - uint32 uid present only if flag SSH_FILEXFER_ATTR_UIDGID - uint32 gid present only if flag SSH_FILEXFER_ATTR_UIDGID - uint32 permissions present only if flag SSH_FILEXFER_ATTR_PERMISSIONS - uint32 atime present only if flag SSH_FILEXFER_ACMODTIME - uint32 mtime present only if flag SSH_FILEXFER_ACMODTIME - uint32 extended_count present only if flag SSH_FILEXFER_ATTR_EXTENDED - string extended_type - string extended_data - ... more extended data (extended_type - extended_data pairs), - so that number of pairs equals extended_count - - The `flags' specify which of the fields are present. Those fields - for which the corresponding flag is not set are not present (not - included in the packet). New flags can only be added by incrementing - the protocol version number (or by using the extension mechanism - described below). - - The `size' field specifies the size of the file in bytes. - - The `uid' and `gid' fields contain numeric Unix-like user and group - identifiers, respectively. - - The `permissions' field contains a bit mask of file permissions as - defined by posix [1]. - - The `atime' and `mtime' contain the access and modification times of - the files, respectively. They are represented as seconds from Jan 1, - 1970 in UTC. - - The SSH_FILEXFER_ATTR_EXTENDED flag provides a general extension - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 8] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - mechanism for vendor-specific extensions. If the flag is specified, - then the `extended_count' field is present. It specifies the number - of extended_type-extended_data pairs that follow. Each of these - pairs specifies an extended attribute. For each of the attributes, - the extended_type field should be a string of the format - "name@domain", where "domain" is a valid, registered domain name and - "name" identifies the method. The IETF may later standardize certain - names that deviate from this format (e.g., that do not contain the - "@" sign). The interpretation of `extended_data' depends on the - type. Implementations SHOULD ignore extended data fields that they - do not understand. - - Additional fields can be added to the attributes by either defining - additional bits to the flags field to indicate their presence, or by - defining extended attributes for them. The extended attributes - mechanism is recommended for most purposes; additional flags bits - should only be defined by an IETF standards action that also - increments the protocol version number. The use of such new fields - MUST be negotiated by the version number in the protocol exchange. - It is a protocol error if a packet with unsupported protocol bits is - received. - - The flags bits are defined to have the following values: - - #define SSH_FILEXFER_ATTR_SIZE 0x00000001 - #define SSH_FILEXFER_ATTR_UIDGID 0x00000002 - #define SSH_FILEXFER_ATTR_PERMISSIONS 0x00000004 - #define SSH_FILEXFER_ATTR_ACMODTIME 0x00000008 - #define SSH_FILEXFER_ATTR_EXTENDED 0x80000000 - - - - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 9] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -6. Requests From the Client to the Server - - Requests from the client to the server represent the various file - system operations. Each request begins with an `id' field, which is - a 32-bit identifier identifying the request (selected by the client). - The same identifier will be returned in the response to the request. - One possible implementation of it is a monotonically increasing - request sequence number (modulo 2^32). - - Many operations in the protocol operate on open files. The - SSH_FXP_OPEN request can return a file handle (which is an opaque - variable-length string) which may be used to access the file later - (e.g. in a read operation). The client MUST NOT send requests the - server with bogus or closed handles. However, the server MUST - perform adequate checks on the handle in order to avoid security - risks due to fabricated handles. - - This design allows either stateful and stateless server - implementation, as well as an implementation which caches state - between requests but may also flush it. The contents of the file - handle string are entirely up to the server and its design. The - client should not modify or attempt to interpret the file handle - strings. - - The file handle strings MUST NOT be longer than 256 bytes. - -6.1 Request Synchronization and Reordering - - The protocol and implementations MUST process requests relating to - the same file in the order in which they are received. In other - words, if an application submits multiple requests to the server, the - results in the responses will be the same as if it had sent the - requests one at a time and waited for the response in each case. For - example, the server may process non-overlapping read/write requests - to the same file in parallel, but overlapping reads and writes cannot - be reordered or parallelized. However, there are no ordering - restrictions on the server for processing requests from two different - file transfer connections. The server may interleave and parallelize - them at will. - - There are no restrictions on the order in which responses to - outstanding requests are delivered to the client, except that the - server must ensure fairness in the sense that processing of no - request will be indefinitely delayed even if the client is sending - other requests so that there are multiple outstanding requests all - the time. - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 10] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -6.2 File Names - - This protocol represents file names as strings. File names are - assumed to use the slash ('/') character as a directory separator. - - File names starting with a slash are "absolute", and are relative to - the root of the file system. Names starting with any other character - are relative to the user's default directory (home directory). Note - that identifying the user is assumed to take place outside of this - protocol. - - Servers SHOULD interpret a path name component ".." as referring to - the parent directory, and "." as referring to the current directory. - If the server implementation limits access to certain parts of the - file system, it must be extra careful in parsing file names when - enforcing such restrictions. There have been numerous reported - security bugs where a ".." in a path name has allowed access outside - the intended area. - - An empty path name is valid, and it refers to the user's default - directory (usually the user's home directory). - - Otherwise, no syntax is defined for file names by this specification. - Clients should not make any other assumptions; however, they can - splice path name components returned by SSH_FXP_READDIR together - using a slash ('/') as the separator, and that will work as expected. - - It is understood that the lack of well-defined semantics for file - names may cause interoperability problems between clients and servers - using radically different operating systems. However, this approach - is known to work acceptably with most systems, and alternative - approaches that e.g. treat file names as sequences of structured - components are quite complicated. - -6.3 Opening, Creating, and Closing Files - - Files are opened and created using the SSH_FXP_OPEN message, whose - data part is as follows: - - uint32 id - string filename - uint32 pflags - ATTRS attrs - - The `id' field is the request identifier as for all requests. - - The `filename' field specifies the file name. See Section ``File - Names'' for more information. - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 11] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - The `pflags' field is a bitmask. The following bits have been - defined. - - #define SSH_FXF_READ 0x00000001 - #define SSH_FXF_WRITE 0x00000002 - #define SSH_FXF_APPEND 0x00000004 - #define SSH_FXF_CREAT 0x00000008 - #define SSH_FXF_TRUNC 0x00000010 - #define SSH_FXF_EXCL 0x00000020 - - These have the following meanings: - - SSH_FXF_READ - Open the file for reading. - - SSH_FXF_WRITE - Open the file for writing. If both this and SSH_FXF_READ are - specified, the file is opened for both reading and writing. - - SSH_FXF_APPEND - Force all writes to append data at the end of the file. - - SSH_FXF_CREAT - If this flag is specified, then a new file will be created if one - does not already exist (if O_TRUNC is specified, the new file will - be truncated to zero length if it previously exists). - - SSH_FXF_TRUNC - Forces an existing file with the same name to be truncated to zero - length when creating a file by specifying SSH_FXF_CREAT. - SSH_FXF_CREAT MUST also be specified if this flag is used. - - SSH_FXF_EXCL - Causes the request to fail if the named file already exists. - SSH_FXF_CREAT MUST also be specified if this flag is used. - - The `attrs' field specifies the initial attributes for the file. - Default values will be used for those attributes that are not - specified. See Section ``File Attributes'' for more information. - - Regardless the server operating system, the file will always be - opened in "binary" mode (i.e., no translations between different - character sets and newline encodings). - - The response to this message will be either SSH_FXP_HANDLE (if the - operation is successful) or SSH_FXP_STATUS (if the operation fails). - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 12] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - A file is closed by using the SSH_FXP_CLOSE request. Its data field - has the following format: - - uint32 id - string handle - - where `id' is the request identifier, and `handle' is a handle - previously returned in the response to SSH_FXP_OPEN or - SSH_FXP_OPENDIR. The handle becomes invalid immediately after this - request has been sent. - - The response to this request will be a SSH_FXP_STATUS message. One - should note that on some server platforms even a close can fail. - This can happen e.g. if the server operating system caches writes, - and an error occurs while flushing cached writes during the close. - -6.4 Reading and Writing - - Once a file has been opened, it can be read using the SSH_FXP_READ - message, which has the following format: - - uint32 id - string handle - uint64 offset - uint32 len - - where `id' is the request identifier, `handle' is an open file handle - returned by SSH_FXP_OPEN, `offset' is the offset (in bytes) relative - to the beginning of the file from where to start reading, and `len' - is the maximum number of bytes to read. - - In response to this request, the server will read as many bytes as it - can from the file (up to `len'), and return them in a SSH_FXP_DATA - message. If an error occurs or EOF is encountered before reading any - data, the server will respond with SSH_FXP_STATUS. For normal disk - files, it is guaranteed that this will read the specified number of - bytes, or up to end of file. For e.g. device files this may return - fewer bytes than requested. - - Writing to a file is achieved using the SSH_FXP_WRITE message, which - has the following format: - - uint32 id - string handle - uint64 offset - string data - - where `id' is a request identifier, `handle' is a file handle - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 13] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - returned by SSH_FXP_OPEN, `offset' is the offset (in bytes) from the - beginning of the file where to start writing, and `data' is the data - to be written. - - The write will extend the file if writing beyond the end of the file. - It is legal to write way beyond the end of the file; the semantics - are to write zeroes from the end of the file to the specified offset - and then the data. On most operating systems, such writes do not - allocate disk space but instead leave "holes" in the file. - - The server responds to a write request with a SSH_FXP_STATUS message. - -6.5 Removing and Renaming Files - - Files can be removed using the SSH_FXP_REMOVE message. It has the - following format: - - uint32 id - string filename - - where `id' is the request identifier and `filename' is the name of - the file to be removed. See Section ``File Names'' for more - information. This request cannot be used to remove directories. - - The server will respond to this request with a SSH_FXP_STATUS - message. - - Files (and directories) can be renamed using the SSH_FXP_RENAME - message. Its data is as follows: - - uint32 id - string oldpath - string newpath - - where `id' is the request identifier, `oldpath' is the name of an - existing file or directory, and `newpath' is the new name for the - file or directory. It is an error if there already exists a file - with the name specified by newpath. The server may also fail rename - requests in other situations, for example if `oldpath' and `newpath' - point to different file systems on the server. - - The server will respond to this request with a SSH_FXP_STATUS - message. - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 14] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -6.6 Creating and Deleting Directories - - New directories can be created using the SSH_FXP_MKDIR request. It - has the following format: - - uint32 id - string path - ATTRS attrs - - where `id' is the request identifier, `path' and `attrs' specifies - the modifications to be made to its attributes. See Section ``File - Names'' for more information on file names. Attributes are discussed - in more detail in Section ``File Attributes''. specifies the - directory to be created. An error will be returned if a file or - directory with the specified path already exists. The server will - respond to this request with a SSH_FXP_STATUS message. - - Directories can be removed using the SSH_FXP_RMDIR request, which - has the following format: - - uint32 id - string path - - where `id' is the request identifier, and `path' specifies the - directory to be removed. See Section ``File Names'' for more - information on file names. An error will be returned if no directory - with the specified path exists, or if the specified directory is not - empty, or if the path specified a file system object other than a - directory. The server responds to this request with a SSH_FXP_STATUS - message. - -6.7 Scanning Directories - - The files in a directory can be listed using the SSH_FXP_OPENDIR and - SSH_FXP_READDIR requests. Each SSH_FXP_READDIR request returns one - or more file names with full file attributes for each file. The - client should call SSH_FXP_READDIR repeatedly until it has found the - file it is looking for or until the server responds with a - SSH_FXP_STATUS message indicating an error (normally SSH_FX_EOF if - there are no more files in the directory). The client should then - close the handle using the SSH_FXP_CLOSE request. - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 15] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - The SSH_FXP_OPENDIR opens a directory for reading. It has the - following format: - - uint32 id - string path - - where `id' is the request identifier and `path' is the path name of - the directory to be listed (without any trailing slash). See Section - ``File Names'' for more information on file names. This will return - an error if the path does not specify a directory or if the directory - is not readable. The server will respond to this request with either - a SSH_FXP_HANDLE or a SSH_FXP_STATUS message. - - Once the directory has been successfully opened, files (and - directories) contained in it can be listed using SSH_FXP_READDIR - requests. These are of the format - - uint32 id - string handle - - where `id' is the request identifier, and `handle' is a handle - returned by SSH_FXP_OPENDIR. (It is a protocol error to attempt to - use an ordinary file handle returned by SSH_FXP_OPEN.) - - The server responds to this request with either a SSH_FXP_NAME or a - SSH_FXP_STATUS message. One or more names may be returned at a time. - Full status information is returned for each name in order to speed - up typical directory listings. - - When the client no longer wishes to read more names from the - directory, it SHOULD call SSH_FXP_CLOSE for the handle. The handle - should be closed regardless of whether an error has occurred or not. - -6.8 Retrieving File Attributes - - Very often, file attributes are automatically returned by - SSH_FXP_READDIR. However, sometimes there is need to specifically - retrieve the attributes for a named file. This can be done using the - SSH_FXP_STAT, SSH_FXP_LSTAT and SSH_FXP_FSTAT requests. - - SSH_FXP_STAT and SSH_FXP_LSTAT only differ in that SSH_FXP_STAT - follows symbolic links on the server, whereas SSH_FXP_LSTAT does not - follow symbolic links. Both have the same format: - - uint32 id - string path - - where `id' is the request identifier, and `path' specifies the file - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 16] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - system object for which status is to be returned. The server - responds to this request with either SSH_FXP_ATTRS or SSH_FXP_STATUS. - - SSH_FXP_FSTAT differs from the others in that it returns status - information for an open file (identified by the file handle). Its - format is as follows: - - uint32 id - string handle - - where `id' is the request identifier and `handle' is a file handle - returned by SSH_FXP_OPEN. The server responds to this request with - SSH_FXP_ATTRS or SSH_FXP_STATUS. - -6.9 Setting File Attributes - - File attributes may be modified using the SSH_FXP_SETSTAT and - SSH_FXP_FSETSTAT requests. These requests are used for operations - such as changing the ownership, permissions or access times, as well - as for truncating a file. - - The SSH_FXP_SETSTAT request is of the following format: - - uint32 id - string path - ATTRS attrs - - where `id' is the request identifier, `path' specifies the file - system object (e.g. file or directory) whose attributes are to be - modified, and `attrs' specifies the modifications to be made to its - attributes. Attributes are discussed in more detail in Section - ``File Attributes''. - - An error will be returned if the specified file system object does - not exist or the user does not have sufficient rights to modify the - specified attributes. The server responds to this request with a - SSH_FXP_STATUS message. - - The SSH_FXP_FSETSTAT request modifies the attributes of a file which - is already open. It has the following format: - - uint32 id - string handle - ATTRS attrs - - where `id' is the request identifier, `handle' (MUST be returned by - SSH_FXP_OPEN) identifies the file whose attributes are to be - modified, and `attrs' specifies the modifications to be made to its - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 17] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - attributes. Attributes are discussed in more detail in Section - ``File Attributes''. The server will respond to this request with - SSH_FXP_STATUS. - -6.10 Dealing with Symbolic links - - The SSH_FXP_READLINK request may be used to read the target of a - symbolic link. It would have a data part as follows: - - uint32 id - string path - - where `id' is the request identifier and `path' specifies the path - name of the symlink to be read. - - The server will respond with a SSH_FXP_NAME packet containing only - one name and a dummy attributes value. The name in the returned - packet contains the target of the link. If an error occurs, the - server may respond with SSH_FXP_STATUS. - - The SSH_FXP_SYMLINK request will create a symbolic link on the - server. It is of the following format - - uint32 id - string linkpath - string targetpath - - where `id' is the request identifier, `linkpath' specifies the path - name of the symlink to be created and `targetpath' specifies the - target of the symlink. The server shall respond with a - SSH_FXP_STATUS indicating either success (SSH_FX_OK) or an error - condition. - -6.11 Canonicalizing the Server-Side Path Name - - The SSH_FXP_REALPATH request can be used to have the server - canonicalize any given path name to an absolute path. This is useful - for converting path names containing ".." components or relative - pathnames without a leading slash into absolute paths. The format of - the request is as follows: - - uint32 id - string path - - where `id' is the request identifier and `path' specifies the path - name to be canonicalized. The server will respond with a - SSH_FXP_NAME packet containing only one name and a dummy attributes - value. The name is the returned packet will be in canonical form. - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 18] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - If an error occurs, the server may also respond with SSH_FXP_STATUS. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 19] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -7. Responses from the Server to the Client - - The server responds to the client using one of a few response - packets. All requests can return a SSH_FXP_STATUS response upon - failure. When the operation is successful, any of the responses may - be returned (depending on the operation). If no data needs to be - returned to the client, the SSH_FXP_STATUS response with SSH_FX_OK - status is appropriate. Otherwise, the SSH_FXP_HANDLE message is used - to return a file handle (for SSH_FXP_OPEN and SSH_FXP_OPENDIR - requests), SSH_FXP_DATA is used to return data from SSH_FXP_READ, - SSH_FXP_NAME is used to return one or more file names from a - SSH_FXP_READDIR or SSH_FXP_REALPATH request, and SSH_FXP_ATTRS is - used to return file attributes from SSH_FXP_STAT, SSH_FXP_LSTAT, and - SSH_FXP_FSTAT requests. - - Exactly one response will be returned for each request. Each - response packet contains a request identifier which can be used to - match each response with the corresponding request. Note that it is - legal to have several requests outstanding simultaneously, and the - server is allowed to send responses to them in a different order from - the order in which the requests were sent (the result of their - execution, however, is guaranteed to be as if they had been processed - one at a time in the order in which the requests were sent). - - Response packets are of the same general format as request packets. - Each response packet begins with the request identifier. - - The format of the data portion of the SSH_FXP_STATUS response is as - follows: - - uint32 id - uint32 error/status code - string error message (ISO-10646 UTF-8 [RFC-2279]) - string language tag (as defined in [RFC-1766]) - - where `id' is the request identifier, and `error/status code' - indicates the result of the requested operation. The value SSH_FX_OK - indicates success, and all other values indicate failure. - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 20] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - Currently, the following values are defined (other values may be - defined by future versions of this protocol): - - #define SSH_FX_OK 0 - #define SSH_FX_EOF 1 - #define SSH_FX_NO_SUCH_FILE 2 - #define SSH_FX_PERMISSION_DENIED 3 - #define SSH_FX_FAILURE 4 - #define SSH_FX_BAD_MESSAGE 5 - #define SSH_FX_NO_CONNECTION 6 - #define SSH_FX_CONNECTION_LOST 7 - #define SSH_FX_OP_UNSUPPORTED 8 - - SSH_FX_OK - Indicates successful completion of the operation. - - SSH_FX_EOF - indicates end-of-file condition; for SSH_FX_READ it means that no - more data is available in the file, and for SSH_FX_READDIR it - indicates that no more files are contained in the directory. - - SSH_FX_NO_SUCH_FILE - is returned when a reference is made to a file which should exist - but doesn't. - - SSH_FX_PERMISSION_DENIED - is returned when the authenticated user does not have sufficient - permissions to perform the operation. - - SSH_FX_FAILURE - is a generic catch-all error message; it should be returned if an - error occurs for which there is no more specific error code - defined. - - SSH_FX_BAD_MESSAGE - may be returned if a badly formatted packet or protocol - incompatibility is detected. - - SSH_FX_NO_CONNECTION - is a pseudo-error which indicates that the client has no - connection to the server (it can only be generated locally by the - client, and MUST NOT be returned by servers). - - SSH_FX_CONNECTION_LOST - is a pseudo-error which indicates that the connection to the - server has been lost (it can only be generated locally by the - client, and MUST NOT be returned by servers). - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 21] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - SSH_FX_OP_UNSUPPORTED - indicates that an attempt was made to perform an operation which - is not supported for the server (it may be generated locally by - the client if e.g. the version number exchange indicates that a - required feature is not supported by the server, or it may be - returned by the server if the server does not implement an - operation). - - The SSH_FXP_HANDLE response has the following format: - - uint32 id - string handle - - where `id' is the request identifier, and `handle' is an arbitrary - string that identifies an open file or directory on the server. The - handle is opaque to the client; the client MUST NOT attempt to - interpret or modify it in any way. The length of the handle string - MUST NOT exceed 256 data bytes. - - The SSH_FXP_DATA response has the following format: - - uint32 id - string data - - where `id' is the request identifier, and `data' is an arbitrary byte - string containing the requested data. The data string may be at most - the number of bytes requested in a SSH_FXP_READ request, but may also - be shorter if end of file is reached or if the read is from something - other than a regular file. - - The SSH_FXP_NAME response has the following format: - - uint32 id - uint32 count - repeats count times: - string filename - string longname - ATTRS attrs - - where `id' is the request identifier, `count' is the number of names - returned in this response, and the remaining fields repeat `count' - times (so that all three fields are first included for the first - file, then for the second file, etc). In the repeated part, - `filename' is a file name being returned (for SSH_FXP_READDIR, it - will be a relative name within the directory, without any path - components; for SSH_FXP_REALPATH it will be an absolute path name), - `longname' is an expanded format for the file name, similar to what - is returned by "ls -l" on Unix systems, and `attrs' is the attributes - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 22] - -Internet-Draft SSH File Transfer Protocol October 2001 - - - of the file as described in Section ``File Attributes''. - - The format of the `longname' field is unspecified by this protocol. - It MUST be suitable for use in the output of a directory listing - command (in fact, the recommended operation for a directory listing - command is to simply display this data). However, clients SHOULD NOT - attempt to parse the longname field for file attributes; they SHOULD - use the attrs field instead. - - The recommended format for the longname field is as follows: - - -rwxr-xr-x 1 mjos staff 348911 Mar 25 14:29 t-filexfer - 1234567890 123 12345678 12345678 12345678 123456789012 - - Here, the first line is sample output, and the second field indicates - widths of the various fields. Fields are separated by spaces. The - first field lists file permissions for user, group, and others; the - second field is link count; the third field is the name of the user - who owns the file; the fourth field is the name of the group that - owns the file; the fifth field is the size of the file in bytes; the - sixth field (which actually may contain spaces, but is fixed to 12 - characters) is the file modification time, and the seventh field is - the file name. Each field is specified to be a minimum of certain - number of character positions (indicated by the second line above), - but may also be longer if the data does not fit in the specified - length. - - The SSH_FXP_ATTRS response has the following format: - - uint32 id - ATTRS attrs - - where `id' is the request identifier, and `attrs' is the returned - file attributes as described in Section ``File Attributes''. - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 23] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -8. Vendor-Specific Extensions - - The SSH_FXP_EXTENDED request provides a generic extension mechanism - for adding vendor-specific commands. The request has the following - format: - - uint32 id - string extended-request - ... any request-specific data ... - - where `id' is the request identifier, and `extended-request' is a - string of the format "name@domain", where domain is an internet - domain name of the vendor defining the request. The rest of the - request is completely vendor-specific, and servers should only - attempt to interpret it if they recognize the `extended-request' - name. - - The server may respond to such requests using any of the response - packets defined in Section ``Responses from the Server to the - Client''. Additionally, the server may also respond with a - SSH_FXP_EXTENDED_REPLY packet, as defined below. If the server does - not recognize the `extended-request' name, then the server MUST - respond with SSH_FXP_STATUS with error/status set to - SSH_FX_OP_UNSUPPORTED. - - The SSH_FXP_EXTENDED_REPLY packet can be used to carry arbitrary - extension-specific data from the server to the client. It is of the - following format: - - uint32 id - ... any request-specific data ... - - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 24] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -9. Security Considerations - - This protocol assumes that it is run over a secure channel and that - the endpoints of the channel have been authenticated. Thus, this - protocol assumes that it is externally protected from network-level - attacks. - - This protocol provides file system access to arbitrary files on the - server (only constrained by the server implementation). It is the - responsibility of the server implementation to enforce any access - controls that may be required to limit the access allowed for any - particular user (the user being authenticated externally to this - protocol, typically using the SSH User Authentication Protocol [6]. - - Care must be taken in the server implementation to check the validity - of received file handle strings. The server should not rely on them - directly; it MUST check the validity of each handle before relying on - it. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 25] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -10. Changes from previous protocol versions - - The SSH File Transfer Protocol has changed over time, before it's - standardization. The following is a description of the incompatible - changes between different versions. - -10.1 Changes between versions 3 and 2 - - o The SSH_FXP_READLINK and SSH_FXP_SYMLINK messages were added. - - o The SSH_FXP_EXTENDED and SSH_FXP_EXTENDED_REPLY messages were - added. - - o The SSH_FXP_STATUS message was changed to include fields `error - message' and `language tag'. - - -10.2 Changes between versions 2 and 1 - - o The SSH_FXP_RENAME message was added. - - -10.3 Changes between versions 1 and 0 - - o Implementation changes, no actual protocol changes. - - - - - - - - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 26] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -11. Trademark Issues - - "ssh" is a registered trademark of SSH Communications Security Corp - in the United States and/or other countries. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 27] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -References - - [1] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and - P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January - 1999. - - [2] Institute of Electrical and Electronics Engineers, "Information - Technology - Portable Operating System Interface (POSIX) - Part - 1: System Application Program Interface (API) [C Language]", - IEEE Standard 1003.2, 1996. - - [3] Rinne, T., Ylonen, T., Kivinen, T., Saarinen, M. and S. - Lehtinen, "SSH Protocol Architecture", draft-ietf-secsh- - architecture-09 (work in progress), July 2001. - - [4] Rinne, T., Ylonen, T., Kivinen, T., Saarinen, M. and S. - Lehtinen, "SSH Protocol Transport Protocol", draft-ietf-secsh- - architecture-09 (work in progress), July 2001. - - [5] Rinne, T., Ylonen, T., Kivinen, T., Saarinen, M. and S. - Lehtinen, "SSH Connection Protocol", draft-ietf-secsh-connect-11 - (work in progress), July 2001. - - [6] Rinne, T., Ylonen, T., Kivinen, T., Saarinen, M. and S. - Lehtinen, "SSH Authentication Protocol", draft-ietf-secsh- - userauth-11 (work in progress), July 2001. - - -Authors' Addresses - - Tatu Ylonen - SSH Communications Security Corp - Fredrikinkatu 42 - HELSINKI FIN-00100 - Finland - - EMail: ylo@ssh.com - - - Sami Lehtinen - SSH Communications Security Corp - Fredrikinkatu 42 - HELSINKI FIN-00100 - Finland - - EMail: sjl@ssh.com - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 28] - -Internet-Draft SSH File Transfer Protocol October 2001 - - -Full Copyright Statement - - Copyright (C) The Internet Society (2001). All Rights Reserved. - - This document and translations of it may be copied and furnished to - others, and derivative works that comment on or otherwise explain it - or assist in its implementation may be prepared, copied, published - and distributed, in whole or in part, without restriction of any - kind, provided that the above copyright notice and this paragraph are - included on all such copies and derivative works. However, this - document itself may not be modified in any way, such as by removing - the copyright notice or references to the Internet Society or other - Internet organizations, except as needed for the purpose of - developing Internet standards in which case the procedures for - copyrights defined in the Internet Standards process must be - followed, or as required to translate it into languages other than - English. - - The limited permissions granted above are perpetual and will not be - revoked by the Internet Society or its successors or assigns. - - This document and the information contained herein is provided on an - "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING - TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING - BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION - HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF - MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. - -Acknowledgement - - Funding for the RFC Editor function is currently provided by the - Internet Society. - - - - - - - - - - - - - - - - - - - -Ylonen & Lehtinen Expires April 1, 2002 [Page 29] - - - |