[PATCH 6.6 321/393] ubifs: skip dumping tnc tree when zroot is null

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: pangliyuan <pangliyuan1@huawei.com>

[ Upstream commit bdb0ca39e0acccf6771db49c3f94ed787d05f2d7 ]

Clearing slab cache will free all znode in memory and make
c->zroot.znode = NULL, then dumping tnc tree will access
c->zroot.znode which cause null pointer dereference.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=219624#c0
Fixes: 1e51764a3c2a ("UBIFS: add new flash file system")
Signed-off-by: pangliyuan <pangliyuan1@huawei.com>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ubifs/debug.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/fs/ubifs/debug.c b/fs/ubifs/debug.c
index eef9e527d9ff9..ff9e574c07a87 100644
--- a/fs/ubifs/debug.c
+++ b/fs/ubifs/debug.c
@@ -946,16 +946,20 @@ void ubifs_dump_tnc(struct ubifs_info *c)
 
 	pr_err("\n");
 	pr_err("(pid %d) start dumping TNC tree\n", current->pid);
-	znode = ubifs_tnc_levelorder_next(c, c->zroot.znode, NULL);
-	level = znode->level;
-	pr_err("== Level %d ==\n", level);
-	while (znode) {
-		if (level != znode->level) {
-			level = znode->level;
-			pr_err("== Level %d ==\n", level);
+	if (c->zroot.znode) {
+		znode = ubifs_tnc_levelorder_next(c, c->zroot.znode, NULL);
+		level = znode->level;
+		pr_err("== Level %d ==\n", level);
+		while (znode) {
+			if (level != znode->level) {
+				level = znode->level;
+				pr_err("== Level %d ==\n", level);
+			}
+			ubifs_dump_znode(c, znode);
+			znode = ubifs_tnc_levelorder_next(c, c->zroot.znode, znode);
 		}
-		ubifs_dump_znode(c, znode);
-		znode = ubifs_tnc_levelorder_next(c, c->zroot.znode, znode);
+	} else {
+		pr_err("empty TNC tree in memory\n");
 	}
 	pr_err("(pid %d) finish dumping TNC tree\n", current->pid);
 }
-- 
2.39.5