buffer: add a hidden canary to detect format errors

Reviewed-by: Andreas Schneider <asn@samba.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/include/libssh/buffer.h b/include/libssh/buffer.h
index 942089f0..a3e093c2 100644
--- a/include/libssh/buffer.h
+++ b/include/libssh/buffer.h
@@ -38,6 +38,8 @@ struct ssh_buffer_struct {
     uint32_t pos;
 };
 
+#define SSH_BUFFER_PACK_END ((uint32_t) 0x4f65feb3)
+
 LIBSSH_API void ssh_buffer_free(ssh_buffer buffer);
 LIBSSH_API void *ssh_buffer_get_begin(ssh_buffer buffer);
 LIBSSH_API uint32_t ssh_buffer_get_len(ssh_buffer buffer);
@@ -49,9 +51,12 @@ int buffer_add_u32(ssh_buffer buffer, uint32_t data);
 int buffer_add_u64(ssh_buffer buffer, uint64_t data);
 int ssh_buffer_add_data(ssh_buffer buffer, const void *data, uint32_t len);
 int ssh_buffer_pack_va(struct ssh_buffer_struct *buffer, const char *format, va_list ap);
-int ssh_buffer_pack(struct ssh_buffer_struct *buffer, const char *format, ...);
+int _ssh_buffer_pack(struct ssh_buffer_struct *buffer, const char *format, ...);
+#define ssh_buffer_pack(buffer, format, ...) _ssh_buffer_pack((buffer),(format), __VA_ARGS__, SSH_BUFFER_PACK_END)
 int ssh_buffer_unpack_va(struct ssh_buffer_struct *buffer, const char *format, va_list ap);
-int ssh_buffer_unpack(struct ssh_buffer_struct *buffer, const char *format, ...);
+int _ssh_buffer_unpack(struct ssh_buffer_struct *buffer, const char *format, ...);
+#define ssh_buffer_unpack(buffer, format, ...) _ssh_buffer_unpack((buffer),(format), __VA_ARGS__, SSH_BUFFER_PACK_END)
+
 int buffer_prepend_data(ssh_buffer buffer, const void *data, uint32_t len);
 int buffer_add_buffer(ssh_buffer buffer, ssh_buffer source);
 int ssh_buffer_reinit(ssh_buffer buffer);