[PATCH 4.9 04/57] cifs: fix incorrect check for null pointer in header_assemble

[Greg Kroah-Hartman]

From: Steve French <stfrench@xxxxxxxxxxxxx>

commit 9ed38fd4a15417cac83967360cf20b853bfab9b6 upstream.

Although very unlikely that the tlink pointer would be null in this case,
get_next_mid function can in theory return null (but not an error)
so need to check for null (not for IS_ERR, which can not be returned
here).

Address warning:

        fs/smbfs_client/connect.c:2392 cifs_match_super()
        warn: 'tlink' isn't an ERR_PTR

Pointed out by Dan Carpenter via smatch code analysis tool

CC: stable@xxxxxxxxxxxxxxx
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Acked-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/cifs/connect.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2960,9 +2960,10 @@ cifs_match_super(struct super_block *sb,
 	spin_lock(&cifs_tcp_ses_lock);
 	cifs_sb = CIFS_SB(sb);
 	tlink = cifs_get_tlink(cifs_sb_master_tlink(cifs_sb));
-	if (IS_ERR(tlink)) {
+	if (tlink == NULL) {
+		/* can not match superblock if tlink were ever null */
 		spin_unlock(&cifs_tcp_ses_lock);
-		return rc;
+		return 0;
 	}
 	tcon = tlink_tcon(tlink);
 	ses = tcon->ses;