btrfs: lzo: reject compressed segment that overflows the compressed input

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, treating it as corruption like the other on-disk validation
failures in this function.

Reported-by: Xiang Mei <xmei5@asu.edu>
Fixes: a6e66e6f8c1b ("btrfs: rework lzo_decompress_bio() to make it subpage compatible")
Assisted-by: Claude:claude-opus-4-8
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c
index 2de18c7b563afdbae9d8f2e099775db6a5617778..6e4aa22853aba20530e7cb17fca83cb7d1e2a164 100644 (file)
--- a/fs/btrfs/lzo.c
+++ b/fs/btrfs/lzo.c
@@ -491,6 +491,17 @@ 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)) {
+                       struct btrfs_inode *inode = cb->bbio.inode;
+
+                       btrfs_err(fs_info,
+                       "lzo segment overflows compressed input, root %llu inode %llu offset %llu cur_in %u len %u compressed len %u",
+                                 btrfs_root_id(inode->root), btrfs_ino(inode),
+                                 cb->start, cur_in, seg_len, compressed_len);
+                       return -EUCLEAN;
+               }
+
                /* Copy the compressed segment payload into workspace */
                copy_compressed_segment(cb, &fi, &cur_folio_index, workspace->cbuf,
                                        seg_len, &cur_in);