fs/smb: Fix inconsistent refcnt update

JIRA: https://issues.redhat.com/browse/RHEL-124956
CVE: CVE-2025-39819

commit ab529e6
Author: Shuhao Fu <sfual@cse.ust.hk>
Date:   Thu Aug 28 02:24:19 2025 +0800

    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>

Signed-off-by: Paulo Alcantara <paalcant@redhat.com>

Author: pcacjr

fs/smb/client/smb2inode.c

@@ -207,8 +207,10 @@ static int smb2_compound_op(const unsigned int xid, struct cifs_tcon *tcon,
 	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];
 
@@ -865,6 +867,7 @@ static int smb2_compound_op(const unsigned int xid, struct cifs_tcon *tcon,
 	    smb2_should_replay(tcon, &retries, &cur_sleep))
 		goto replay_again;
 
+out:
 	if (cfile)
 		cifsFileInfo_put(cfile);