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

[Vasiliy Kovalev <kovalev@altlinux.org>]

The l_tree_depth field in struct ocfs2_extent_list is defined
as __le16, but according to the comments in the structure
definition, the high 8 bits must not be used, meaning its
maximum valid value is 255.

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>
---
 fs/ocfs2/extent_map.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/ocfs2/extent_map.c b/fs/ocfs2/extent_map.c
index 930150ed5db15..0d9c25fdec029 100644
--- a/fs/ocfs2/extent_map.c
+++ b/fs/ocfs2/extent_map.c
@@ -415,6 +415,15 @@ static int ocfs2_get_clusters_nocache(struct inode *inode,
 	tree_height = le16_to_cpu(el->l_tree_depth);
 
 	if (tree_height > 0) {
+		if (unlikely(tree_height > 255)) {
+			ocfs2_error(inode->i_sb,
+				    "Inode %lu has too large l_tree_depth=%u in leaf block %llu\n",
+				    inode->i_ino, tree_height,
+				    (unsigned long long)di_bh->b_blocknr);
+			ret = -EROFS;
+			goto out;
+		}
+
 		ret = ocfs2_find_leaf(INODE_CACHE(inode), el, v_cluster,
 				      &eb_bh);
 		if (ret) {
-- 
2.42.2