fs/smb: Fix inconsistent refcnt update

A possible inconsistent update of refcount was identified in `smb2_compound_op`.
Such inconsistent update could lead to possible resource leaks.

Why it is a possible bug:
1. In the comment section of the function, it clearly states that the
reference to `cfile` should be dropped after calling this function.
2. Every control flow path would check and drop the reference to
`cfile`, except the patched one.
3. Existing callers would not handle refcount update of `cfile` if
-ENOMEM is returned.

To fix the bug, an extra goto label "out" is added, to make sure that the
cleanup logic would always be respected. As the problem is caused by the
allocation failure of `vars`, the cleanup logic between label "finished"
and "out" can be safely ignored. According to the definition of function
`is_replayable_error`, the error code of "-ENOMEM" is not recoverable.
Therefore, the replay logic also gets ignored.

Signed-off-by: Shuhao Fu <sfual@cse.ust.hk>
Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/smb2inode.c b/fs/smb/client/smb2inode.c
index 2a0316c514e4731d7522b1a715afe9f14c260494..31c13fb5b85b629419e5b531da07aaa93d58edb8 100644 (file)
--- a/fs/smb/client/smb2inode.c
+++ b/fs/smb/client/smb2inode.c
@@ -207,8 +207,10 @@ replay_again:
        server = cifs_pick_channel(ses);
 
        vars = kzalloc(sizeof(*vars), GFP_ATOMIC);
-       if (vars == NULL)
-               return -ENOMEM;
+       if (vars == NULL) {
+               rc = -ENOMEM;
+               goto out;
+       }
        rqst = &vars->rqst[0];
        rsp_iov = &vars->rsp_iov[0];
 
@@ -864,6 +866,7 @@ finished:
            smb2_should_replay(tcon, &retries, &cur_sleep))
                goto replay_again;
 
+out:
        if (cfile)
                cifsFileInfo_put(cfile);