From: Ronnie Sahlberg <lsahlber@redhat.com>
Date: Wed, 13 Apr 2022 10:02:17 +1000
Subject: [PATCH] cifs: verify that tcon is valid before dereference in
 cifs_kill_sb
Git-commit: 8b6c58458ee3206dde345fce327a4cb83e69caf9
References: bsc#1190317
Patch-mainline: v5.18-rc3

On umount, cifs_sb->tlink_tree might contain entries that do not represent
a valid tcon.
Check the tcon for error before we dereference it.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Cc: stable@vger.kernel.org
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Reported-by: Xiaoli Feng <xifeng@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Acked-by: Enzo Matsumiya <ematsumiya@suse.de>
---
 fs/cifs/cifsfs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index aba0783a8f09..2b1a1c029c75 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -266,10 +266,11 @@ static void cifs_kill_sb(struct super_block *sb)
 	 * before we kill the sb.
 	 */
 	if (cifs_sb->root) {
-		node = rb_first(root);
-		while (node != NULL) {
+		for (node = rb_first(root); node; node = rb_next(node)) {
 			tlink = rb_entry(node, struct tcon_link, tl_rbnode);
 			tcon = tlink_tcon(tlink);
+			if (IS_ERR(tcon))
+				continue;
 			cfid = &tcon->crfid;
 			mutex_lock(&cfid->fid_mutex);
 			if (cfid->dentry) {
@@ -277,7 +278,6 @@ static void cifs_kill_sb(struct super_block *sb)
 				cfid->dentry = NULL;
 			}
 			mutex_unlock(&cfid->fid_mutex);
-			node = rb_next(node);
 		}
 
 		/* finally release root dentry */
-- 
2.35.3