[PATCH v2] ocfs2: validate l_tree_depth to avoid out-of-bounds access

[Vasiliy Kovalev <kovalev@altlinux.org>]

The l_tree_depth field is 16-bit (__le16), but the actual
maximum depth is limited to OCFS2_MAX_PATH_DEPTH.

Add a check to prevent out-of-bounds access if l_tree_depth
has an invalid value, which may occur when reading from a
corrupted mounted disk [1].

Fixes: ccd979bdbce9 ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem")
Reported-by: syzbot+66c146268dc88f4341fd@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=66c146268dc88f4341fd [1]
Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
---
v2: Restricted depth to OCFS2_MAX_PATH_DEPTH and moved the check
    to __ocfs2_find_path().
---
 fs/ocfs2/alloc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
index 4414743b638e8..cec8fc5cb8e87 100644
--- a/fs/ocfs2/alloc.c
+++ b/fs/ocfs2/alloc.c
@@ -1803,6 +1803,14 @@ static int __ocfs2_find_path(struct ocfs2_caching_info *ci,
 
 	el = root_el;
 	while (el->l_tree_depth) {
+		if (unlikely(le16_to_cpu(el->l_tree_depth) > OCFS2_MAX_PATH_DEPTH)) {
+			ocfs2_error(ocfs2_metadata_cache_get_super(ci),
+				    "Owner %llu has invalid tree depth %u in extent list\n",
+				    (unsigned long long)ocfs2_metadata_cache_owner(ci),
+				    le16_to_cpu(el->l_tree_depth));
+			ret = -EROFS;
+			goto out;
+		}
 		if (le16_to_cpu(el->l_next_free_rec) == 0) {
 			ocfs2_error(ocfs2_metadata_cache_get_super(ci),
 				    "Owner %llu has empty extent list at depth %u\n",
-- 
2.42.2