Re: [PATCH] ocfs2: validate directory-index entry counts when reading metadata

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

On 7/14/26 4:56 AM, Doruk Tan Ozturk wrote:
> ocfs2_validate_dx_leaf() and ocfs2_validate_dx_root() check the ECC and
> signature of an indexed-directory block before it reaches higher-level
> callers, but neither validator bounds the ocfs2_dx_entry_list counts
> against the capacity of the block that holds them.
> 
> ocfs2_dx_dir_search() then walks
> 
> 	for (i = 0; i < le16_to_cpu(entry_list->de_num_used); i++)
> 		dx_entry = &entry_list->de_entries[i];
> 
> over de_num_used entries with no bounds check.  entry_list is either
> dx_leaf->dl_list (from ocfs2_read_dx_leaf) or, for an inline root,
> dx_root->dr_entries.  A crafted on-disk image can set de_num_used (and
> de_count, which is the __counted_by_le() bound of de_entries) to 0xffff
> and make the walk read far past the end of the 4KB metadata block, giving
> a slab out-of-bounds read reachable from any path lookup, stat() or open()
> on an indexed directory once the image is mounted.
> 
> Commit 775c17386a6f ("ocfs2: validate dx_root extent list fields during
> block read") already bounds dr_list for the non-inline dx_root, but left
> the inline dr_entries path and the dx_leaf dl_list unchecked.  Add the
> same read-time validation for both entry lists: de_count must equal the
> capacity of the block (ocfs2_dx_entries_per_leaf()/per_root()) and
> de_num_used must not exceed de_count, rejecting corrupted metadata with
> -EFSCORRUPTED before ocfs2_dx_dir_search() can walk an out-of-range entry
> array.
> 
> de_count is always written as exactly the block capacity when a leaf or
> inline root is formatted, so the equality check does not reject any
> valid image.
> 
> Fixes: 9b7895efac90 ("ocfs2: Add a name indexed b-tree to directory inodes")
> Fixes: 4ed8a6bb083b ("ocfs2: Store dir index records inline")
> Cc: stable@vger.kernel.org
> Found by 0sec automated security-research tooling (https://0sec.ai).
> Assisted-by: 0sec:claude-opus-4-8
> Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>

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

> ---
>  fs/ocfs2/dir.c | 45 +++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 41 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
> index baf3eca7b4e4..fcc3721cbe34 100644
> --- a/fs/ocfs2/dir.c
> +++ b/fs/ocfs2/dir.c
> @@ -624,6 +624,28 @@ static int ocfs2_validate_dx_root(struct super_block *sb,
>  					  le16_to_cpu(el->l_count));
>  			goto bail;
>  		}
> +	} else {
> +		struct ocfs2_dx_entry_list *dl_list = &dx_root->dr_entries;
> +
> +		if (le16_to_cpu(dl_list->de_count) !=
> +		    ocfs2_dx_entries_per_root(sb)) {
> +			ret = ocfs2_error(sb,
> +					  "Dir Index Root # %llu has invalid de_count %u (expected %u)\n",
> +					  (unsigned long long)le64_to_cpu(dx_root->dr_blkno),
> +					  le16_to_cpu(dl_list->de_count),
> +					  ocfs2_dx_entries_per_root(sb));
> +			goto bail;
> +		}
> +
> +		if (le16_to_cpu(dl_list->de_num_used) >
> +		    le16_to_cpu(dl_list->de_count)) {
> +			ret = ocfs2_error(sb,
> +					  "Dir Index Root # %llu has invalid de_num_used %u (de_count %u)\n",
> +					  (unsigned long long)le64_to_cpu(dx_root->dr_blkno),
> +					  le16_to_cpu(dl_list->de_num_used),
> +					  le16_to_cpu(dl_list->de_count));
> +			goto bail;
> +		}
>  	}
>  
>  bail:
> @@ -663,10 +685,25 @@ static int ocfs2_validate_dx_leaf(struct super_block *sb,
>  		return ret;
>  	}
>  
> -	if (!OCFS2_IS_VALID_DX_LEAF(dx_leaf)) {
> -		ret = ocfs2_error(sb, "Dir Index Leaf has bad signature %.*s\n",
> -				  7, dx_leaf->dl_signature);
> -	}
> +	if (!OCFS2_IS_VALID_DX_LEAF(dx_leaf))
> +		return ocfs2_error(sb, "Dir Index Leaf has bad signature %.*s\n",
> +				   7, dx_leaf->dl_signature);
> +
> +	if (le16_to_cpu(dx_leaf->dl_list.de_count) !=
> +	    ocfs2_dx_entries_per_leaf(sb))
> +		return ocfs2_error(sb,
> +				   "Dir Index Leaf # %llu has invalid de_count %u (expected %u)\n",
> +				   (unsigned long long)le64_to_cpu(dx_leaf->dl_blkno),
> +				   le16_to_cpu(dx_leaf->dl_list.de_count),
> +				   ocfs2_dx_entries_per_leaf(sb));
> +
> +	if (le16_to_cpu(dx_leaf->dl_list.de_num_used) >
> +	    le16_to_cpu(dx_leaf->dl_list.de_count))
> +		return ocfs2_error(sb,
> +				   "Dir Index Leaf # %llu has invalid de_num_used %u (de_count %u)\n",
> +				   (unsigned long long)le64_to_cpu(dx_leaf->dl_blkno),
> +				   le16_to_cpu(dx_leaf->dl_list.de_num_used),
> +				   le16_to_cpu(dx_leaf->dl_list.de_count));
>  
>  	return ret;
>  }