Re: [PATCH v4] ocfs2: fix UBSAN array-index-out-of-bounds in ocfs2_sum_rightmost_rec

[Ian Bridges]

On Fri, Jun 12, 2026 at 09:02:18AM +0800, Joseph Qi wrote:
> 
> 
> On 6/11/26 8:23 AM, Ian Bridges wrote:
> > [BUG]
> > On-disk corruption setting l_next_free_rec to 0 in an inode's embedded
> > extent list triggers a UBSAN panic on the next write to that file.
> > 
> > [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 embedded 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Closes: https://syzkaller.appspot.com/bug?extid=be16e33db01e6644db7a
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Ian Bridges <icb@xxxxxxxxxxxx>
> 
> Looks fine.
> Reviewed-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
> 
> > ---
> > Changes in 4:
> >  - Update commit message to use "inline" instead of "embedded"
> 
> Typo here? I think you mean 'embedded' instead of 'inline'.
>

Yes, the placement of the "inline" and "embedded" should have been
swapped.

Ian

> >  
> > v3: https://lore.kernel.org/all/aibMhhAH-swS38i0@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:
>