Check for OpenSSH and implement sftp_symlink correct.

When OpenSSH's sftp-server was implemented, the order of the arguments
to the SSH_FXP_SYMLINK method was inadvertently reversed. Unfortunately,
the reversal was not noticed until the server was widely deployed.
Since fixing this to follow the specification would cause
incompatibility, the current order was retained.

2 files changed, 59 insertions, 5 deletions

diff --git a/libssh/client.c b/libssh/client.c
index 5fdec8ee..2ef5568e 100644
--- a/libssh/client.c
+++ b/libssh/client.c
@@ -98,7 +98,10 @@ char *ssh_get_banner(SSH_SESSION *session) {
  * @see ssh_get_banner()
  */
 static int ssh_analyze_banner(SSH_SESSION *session, int *ssh1, int *ssh2) {
-  char *banner = session->serverbanner;
+  const char *banner = session->serverbanner;
+  const char *openssh;
+
+  ssh_log(session, SSH_LOG_RARE, "Analyzing banner: %s", banner);
 
   if (strncmp(banner, "SSH-", 4) != 0) {
     ssh_set_error(session, SSH_FATAL, "Protocol mismatch: %s", banner);
@@ -129,6 +132,17 @@ static int ssh_analyze_banner(SSH_SESSION *session, int *ssh1, int *ssh2) {
       return -1;
   }
 
+  openssh = strstr(banner, "OpenSSH");
+  if (openssh != NULL) {
+    int major, minor;
+    major = strtol(openssh + 8, (char **) NULL, 10);
+    minor = strtol(openssh + 10, (char **) NULL, 10);
+    session->openssh = SSH_VERSION_INT(major, minor, 0);
+    ssh_log(session, SSH_LOG_RARE,
+        "We are talking to an OpenSSH server version: %d.%d (%x)",
+        major, minor, session->openssh);
+  }
+
   return 0;
 }
 
@@ -621,6 +635,24 @@ char *ssh_get_issue_banner(SSH_SESSION *session) {
 }
 
 /**
+ * @brief Get the version of the OpenSSH server, if it is not an OpenSSH server
+ * then 0 will be returned.
+ *
+ * You can use the SSH_VERSION_INT macro to compare version numbers.
+ *
+ * @param  session      The SSH session to use.
+ *
+ * @return The version number if available, 0 otherwise.
+ */
+int ssh_get_openssh_version(SSH_SESSION *session) {
+  if (session == NULL) {
+    return 0;
+  }
+
+  return session->openssh;
+}
+
+/**
  * @brief Disconnect from a session (client or server).
  *
  * @param session       The SSH session to disconnect.
diff --git a/libssh/sftp.c b/libssh/sftp.c
index e86a262b..f720aa58 100644
--- a/libssh/sftp.c
+++ b/libssh/sftp.c
@@ -2243,10 +2243,32 @@ int sftp_symlink(SFTP_SESSION *sftp, const char *target, const char *dest) {
   }
 
   id = sftp_get_new_id(sftp);
-  if (buffer_add_u32(buffer, id) < 0 ||
-      buffer_add_ssh_string(buffer, target_s) < 0 ||
-      buffer_add_ssh_string(buffer, dest_s) < 0 ||
-      sftp_packet_write(sftp, SSH_FXP_SYMLINK, buffer) < 0) {
+  if (buffer_add_u32(buffer, id) < 0) {
+    buffer_free(buffer);
+    string_free(dest_s);
+    string_free(target_s);
+    return -1;
+  }
+  if (ssh_get_openssh_version(sftp->session)) {
+    /* TODO check for version number if they ever fix it. */
+    if (buffer_add_ssh_string(buffer, target_s) < 0 ||
+      buffer_add_ssh_string(buffer, dest_s) < 0) {
+      buffer_free(buffer);
+      string_free(dest_s);
+      string_free(target_s);
+      return -1;
+    }
+  } else {
+    if (buffer_add_ssh_string(buffer, dest_s) < 0 ||
+      buffer_add_ssh_string(buffer, target_s) < 0) {
+      buffer_free(buffer);
+      string_free(dest_s);
+      string_free(target_s);
+      return -1;
+    }
+  }
+
+  if (sftp_packet_write(sftp, SSH_FXP_SYMLINK, buffer) < 0) {
     buffer_free(buffer);
     string_free(dest_s);
     string_free(target_s);