Re: [PATCH] btrfs: lzo: reject compressed segment that overflows the compressed input

[Weiming Shi <bestswngs@gmail.com>]

On 26-06-07 08:02, Qu Wenruo wrote:
> 
> 
> 在 2026/6/7 03:18, Weiming Shi 写道:
> > lzo_decompress_bio() validates each on-disk segment length seg_len only
> > against the workspace cbuf size, not against the compressed input size
> > (compressed_len, the total folio bytes of the bio).  A crafted extent can
> > carry a segment whose seg_len passes the cbuf check but runs past the end
> > of the bio, so copy_compressed_segment() walks off the last folio:
> > get_current_folio() then returns the NULL folio from bio_next_folio(), and
> > with CONFIG_BTRFS_ASSERT disabled (default) folio_size(NULL) faults.
> > 
> >   BUG: KASAN: null-ptr-deref in lzo_decompress_bio (fs/btrfs/lzo.c:383)
> >   Read of size 8 at addr 0000000000000000 by task kworker/u8:1/29
> >   Workqueue: btrfs-endio simple_end_io_work
> >    kasan_report (mm/kasan/report.c:590)
> >    lzo_decompress_bio (fs/btrfs/lzo.c:383)
> >    end_bbio_compressed_read (fs/btrfs/compression.c:1065)
> >    btrfs_bio_end_io (fs/btrfs/bio.c:135)
> >    btrfs_check_read_bio (fs/btrfs/bio.c:180 fs/btrfs/bio.c:285)
> >    simple_end_io_work
> >    process_one_work
> >    worker_thread
> > 
> > Reject any segment whose payload would extend beyond compressed_len before
> > copying it.
> > 
> > Fixes: a6e66e6f8c1b ("btrfs: rework lzo_decompress_bio() to make it subpage compatible")
> > Reported-by: Xiang Mei <xmei5@asu.edu>
> > Assisted-by: Claude:claude-opus-4-8
> > Signed-off-by: Weiming Shi <bestswngs@gmail.com>
> > ---
> >   fs/btrfs/lzo.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> > 
> > diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c
> > index 2de18c7b563a..887d740b27aa 100644
> > --- a/fs/btrfs/lzo.c
> > +++ b/fs/btrfs/lzo.c
> > @@ -491,6 +491,10 @@ int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
> >   			return -EIO;
> >   		}
> > +		/* The segment must not extend beyond the compressed input. */
> > +		if (unlikely(cur_in + seg_len > compressed_len))
> > +			return -EIO;
> > +
> 
> In lzo_decompress() we return -EUCLEAN, please follow that pattern.
> 
> Although it would be better to output a message when such -EUCLEAN is
> returned.
> 
> Otherwise looks good to me.
> 
> Thanks,
> Qu
> 
> >   		/* Copy the compressed segment payload into workspace */
> >   		copy_compressed_segment(cb, &fi, &cur_folio_index, workspace->cbuf,
> >   					seg_len, &cur_in);
> 

Thanks for the review. v2 sent.

Thanks,
Weiming Shi