Re: [PATCH v3] ocfs2: fix UBSAN array-index-out-of-bounds in ocfs2_sum_rightmost_rec

[Ian Bridges <icb@fastmail.org>]

On Mon, Jun 08, 2026 at 09:07:05AM -0500, Ian Bridges wrote:
> [BUG]
> On-disk corruption setting l_next_free_rec to 0 in an inode's inline
> extent list triggers an UBSAN panic on the next write to that file.
>

I misread the recommendation on the previous patch review regarding
"inline" vs "embedded". I will release a v4 with the correct
terminology.

Ian

> [CAUSE]
> ocfs2_sum_rightmost_rec() computes
> i = le16_to_cpu(el->l_next_free_rec) - 1
> and accesses el->l_recs[i] without validating i. When l_next_free_rec
> is 0, i becomes -1; when l_next_free_rec exceeds l_count, i falls
> past the end of the array. Either case violates the
> __counted_by_le(l_count) annotation on l_recs[] and triggers UBSAN.
> 
> [FIX]
> Validate the inode's inline extent list when the inode is read, in
> ocfs2_validate_inode_block(): l_count must be non-zero and no larger
> than the inode block can hold, and l_next_free_rec must not exceed
> l_count. A corrupt list is rejected at read time, before the b-tree
> code can index l_recs[] out of bounds.
> 
> Reported-by: syzbot+be16e33db01e6644db7a@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=be16e33db01e6644db7a
> Cc: stable@vger.kernel.org
> Signed-off-by: Ian Bridges <icb@fastmail.org>
> ---
> Changes in v3:
>  - Update commit message to use "inline" instead of "embedded"
>  - CC stable@vger.kernel.org
>  
> v2: https://lore.kernel.org/all/aiLNd9gAuCC5u2jf@dev/
> 
>  fs/ocfs2/inode.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
> index a510a0eb1adc..aff95efd78e7 100644
> --- a/fs/ocfs2/inode.c
> +++ b/fs/ocfs2/inode.c
> @@ -1559,6 +1559,38 @@ int ocfs2_validate_inode_block(struct super_block *sb,
>  		goto bail;
>  	}
>  
> +	if (ocfs2_dinode_has_extents(di)) {
> +		struct ocfs2_extent_list *el = &di->id2.i_list;
> +		u16 count = le16_to_cpu(el->l_count);
> +		u16 next_free = le16_to_cpu(el->l_next_free_rec);
> +
> +		if (count == 0) {
> +			rc = ocfs2_error(sb,
> +					 "Invalid dinode %llu: extent list l_count is zero\n",
> +					 (unsigned long long)bh->b_blocknr);
> +			goto bail;
> +		}
> +		/*
> +		 * The exact capacity depends on i_xattr_inline_size, another
> +		 * unvalidated on-disk field. Inline xattrs only shrink the
> +		 * list, so the no-xattr maximum is a safe upper bound that a
> +		 * valid l_count never exceeds.
> +		 */
> +		if (count > ocfs2_extent_recs_per_inode(sb)) {
> +			rc = ocfs2_error(sb,
> +					 "Invalid dinode %llu: extent list l_count %u exceeds max %u\n",
> +					 (unsigned long long)bh->b_blocknr, count,
> +					 ocfs2_extent_recs_per_inode(sb));
> +			goto bail;
> +		}
> +		if (next_free > count) {
> +			rc = ocfs2_error(sb,
> +					 "Invalid dinode %llu: extent list l_next_free_rec %u exceeds l_count %u\n",
> +					 (unsigned long long)bh->b_blocknr, next_free, count);
> +			goto bail;
> +		}
> +	}
> +
>  	rc = 0;
>  
>  bail:
> -- 
> 2.47.3
>