[PATCH] ocfs2: fix array out of bound access in __ocfs2_find_path()

[Giorgi Kobakhia]

__ocfs2_find_path() walks down the extent tree and records path by calling
find_path_ins(), which appends entry to path->p_node[]. It only has 5
spots.

A corrupted ocfs2 image whose extent block is pointing to itself causes
__ocfs2_find_path() descent endlessly, writing past the end of
path->p_node[] array.

 UBSAN: array-index-out-of-bounds in fs/ocfs2/alloc.c:677:14
 index 5 is out of range for type 'ocfs2_path_item [5]'
 Call Trace:
  <TASK>
  find_path_ins (fs/ocfs2/alloc.c:677 fs/ocfs2/alloc.c:1914)
  __ocfs2_find_path.constprop.0 (fs/ocfs2/alloc.c:1882)
  ocfs2_commit_truncate (fs/ocfs2/alloc.c:1924 fs/ocfs2/alloc.c:7286)
  ocfs2_truncate_file (fs/ocfs2/file.c:515)
  ocfs2_setattr (fs/ocfs2/file.c:1224)
  notify_change (fs/attr.c:556)
  do_truncate (fs/open.c:68)
  do_ftruncate (fs/open.c:194 (discriminator 1))
  ksys_ftruncate (fs/open.c:206)
  __x64_sys_ftruncate (fs/open.c:211 fs/open.c:209 fs/open.c:209)

Commit a406aff8c051 ("ocfs2: validate l_tree_depth to avoid
out-of-bounds access") already restricts el->l_tree_depth to be less than
OCFS2_MAX_PATH_DEPTH, which is equal to 5. However, does not handle the
infinite descent case.

Check if the el->l_tree_depth decreases on each descent. Maximum
descents are restricted to 4 and the path->p_node[] array does not
overflow.

Fixes: dcd0538ff4e8 ("ocfs2: sparse b-tree support")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: LLM
Tested-by: Xiang Mei <xmei5@xxxxxxx>
Signed-off-by: Giorgi Kobakhia <gkobakhi@xxxxxxx>
---
 fs/ocfs2/alloc.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
index be09e766ac1f..c85a472965d5 100644
--- a/fs/ocfs2/alloc.c
+++ b/fs/ocfs2/alloc.c
@@ -1817,6 +1817,7 @@ static int __ocfs2_find_path(struct ocfs2_caching_info *ci,
 	int i, ret = 0;
 	u32 range;
 	u64 blkno;
+	u32 prev_depth = OCFS2_MAX_PATH_DEPTH;
 	struct buffer_head *bh = NULL;
 	struct ocfs2_extent_block *eb;
 	struct ocfs2_extent_list *el;
@@ -1824,14 +1825,16 @@ 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)) {
+		if (unlikely(le16_to_cpu(el->l_tree_depth) >= prev_depth)) {
 			ocfs2_error(ocfs2_metadata_cache_get_super(ci),
-				    "Owner %llu has invalid tree depth %u in extent list\n",
+				    "Owner %llu has invalid tree depth %u in extent list (max %u)\n",
 				    (unsigned long long)ocfs2_metadata_cache_owner(ci),
-				    le16_to_cpu(el->l_tree_depth));
+				    le16_to_cpu(el->l_tree_depth), prev_depth - 1);
 			ret = -EROFS;
 			goto out;
 		}
+		prev_depth = le16_to_cpu(el->l_tree_depth);
+
 		if (!el->l_next_free_rec || !el->l_count) {
 			ocfs2_error(ocfs2_metadata_cache_get_super(ci),
 				    "Owner %llu has empty extent list at depth %u\n"
-- 
2.43.0