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

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 9/23/26 4:21 AM, Giorgi Kobakhia wrote:
> __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@vger.kernel.org
> Assisted-by: LLM
> Tested-by: Xiang Mei <xmei5@asu.edu>
> Signed-off-by: Giorgi Kobakhia <gkobakhi@asu.edu>

Looks fine.
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>

> ---
>  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"