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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Ronnie Sahlberg <lsahlber@redhat.com>,
        Shyam Prasad N <sprasad@microsoft.com>,
        Xiaoli Feng <xifeng@redhat.com>,
        Steve French <stfrench@microsoft.com>
Subject: [PATCH 5.17 187/219] cifs: verify that tcon is valid before dereference in cifs_kill_sb
Date:   Mon, 18 Apr 2022 14:12:36 +0200
Message-Id: <20220418121212.112167732@linuxfoundation.org>
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From: Ronnie Sahlberg <lsahlber@redhat.com>

commit 8b6c58458ee3206dde345fce327a4cb83e69caf9 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/cifs/cifsfs.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -266,10 +266,11 @@ static void cifs_kill_sb(struct super_bl
 	 * 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_bl
 				cfid->dentry = NULL;
 			}
 			mutex_unlock(&cfid->fid_mutex);
-			node = rb_next(node);
 		}
 
 		/* finally release root dentry */