sftpserver: Support some openssh extensions

Add support for "hardlink@openssh.com" and
"posix-rename@openssh.com" extensions.

Signed-off-by: Chris Townsend <christopher.townsend@canonical.com>
Signed-off-by: Alberto Aguirre <albaguirre@gmail.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/sftp.h

@@ -135,6 +135,7 @@ struct sftp_client_message_struct {
     ssh_string data; /* can be newpath of rename() */
     ssh_buffer complete_message; /* complete message in case of retransmission*/
     char *str_data; /* cstring version of data */
+    char *submessage; /* for extended messages */
 };
 
 struct sftp_request_queue_struct {
@@ -863,6 +864,7 @@ LIBSSH_API const char *sftp_client_message_get_filename(sftp_client_message msg)
 LIBSSH_API void sftp_client_message_set_filename(sftp_client_message msg, const char *newname);
 LIBSSH_API const char *sftp_client_message_get_data(sftp_client_message msg);
 LIBSSH_API uint32_t sftp_client_message_get_flags(sftp_client_message msg);
+LIBSSH_API const char *sftp_client_message_get_submessage(sftp_client_message msg);
 LIBSSH_API int sftp_send_client_message(sftp_session sftp, sftp_client_message msg);
 LIBSSH_API int sftp_reply_name(sftp_client_message msg, const char *name,
     sftp_attributes attr);
@@ -1012,6 +1014,7 @@ LIBSSH_API void sftp_handle_remove(sftp_session sftp, void *handle);
 #define SFTP_RENAME SSH_FXP_RENAME
 #define SFTP_READLINK SSH_FXP_READLINK
 #define SFTP_SYMLINK SSH_FXP_SYMLINK
+#define SFTP_EXTENDED SSH_FXP_EXTENDED
 
 /* openssh flags */
 #define SSH_FXE_STATVFS_ST_RDONLY 0x1 /* read-only */

src/sftp.c

@@ -222,6 +222,7 @@ int sftp_server_init(sftp_session sftp){
   sftp_packet packet = NULL;
   ssh_buffer reply = NULL;
   uint32_t version;
+  int rc;
 
   packet = sftp_packet_read(sftp);
   if (packet == NULL) {
@@ -249,7 +250,13 @@ int sftp_server_init(sftp_session sftp){
     return -1;
   }
 
-  if (ssh_buffer_add_u32(reply, ntohl(LIBSFTP_VERSION)) < 0) {
+  rc = ssh_buffer_pack(reply, "dssss",
+                      LIBSFTP_VERSION,
+                      "posix-rename@openssh.com",
+                      "1",
+                      "hardlink@openssh.com",
+                      "1");
+  if (rc != SSH_OK) {
     ssh_set_error_oom(session);
     ssh_buffer_free(reply);
     return -1;

src/sftpserver.c

@@ -202,6 +202,29 @@ sftp_client_message sftp_get_client_message(sftp_session sftp) {
         return NULL;
       }
       break;
+    case SSH_FXP_EXTENDED:
+      rc = ssh_buffer_unpack(payload,
+                             "s",
+                             &msg->submessage);
+      if (rc != SSH_OK) {
+        ssh_set_error_oom(session);
+        sftp_client_message_free(msg);
+        return NULL;
+      }
+
+      if (strcmp(msg->submessage, "hardlink@openssh.com") == 0 ||
+          strcmp(msg->submessage, "posix-rename@openssh.com") == 0) {
+        rc = ssh_buffer_unpack(payload,
+                               "sS",
+                               &msg->filename,
+                               &msg->data);
+        if (rc != SSH_OK) {
+          ssh_set_error_oom(session);
+          sftp_client_message_free(msg);
+          return NULL;
+        }
+      }
+      break;
     default:
       ssh_set_error(sftp->session, SSH_FATAL,
                     "Received unhandled sftp message %d", msg->type);
@@ -242,12 +265,17 @@ uint32_t sftp_client_message_get_flags(sftp_client_message msg){
 	return msg->flags;
 }
 
+const char *sftp_client_message_get_submessage(sftp_client_message msg){
+        return msg->submessage;
+}
+
 void sftp_client_message_free(sftp_client_message msg) {
   if (msg == NULL) {
     return;
   }
 
   SAFE_FREE(msg->filename);
+  SAFE_FREE(msg->submessage);
   ssh_string_free(msg->data);
   ssh_string_free(msg->handle);
   sftp_attributes_free(msg->attr);