btrfs: fix a use-after-free when hitting errors inside btrfs_submit_c…

…hunk()

[BUG]
There is an internal report that KASAN is reporting use-after-free, with
the following backtrace:

  BUG: KASAN: slab-use-after-free in btrfs_check_read_bio+0xa68/0xb70 [btrfs]
  Read of size 4 at addr ffff8881117cec28 by task kworker/u16:2/45
  CPU: 1 UID: 0 PID: 45 Comm: kworker/u16:2 Not tainted 6.11.0-rc2-next-20240805-default+ Rust-for-Linux#76
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.2-3-gd478f380-rebuilt.opensuse.org 04/01/2014
  Workqueue: btrfs-endio btrfs_end_bio_work [btrfs]
  Call Trace:
   dump_stack_lvl+0x61/0x80
   print_address_description.constprop.0+0x5e/0x2f0
   print_report+0x118/0x216
   kasan_report+0x11d/0x1f0
   btrfs_check_read_bio+0xa68/0xb70 [btrfs]
   process_one_work+0xce0/0x12a0
   worker_thread+0x717/0x1250
   kthread+0x2e3/0x3c0
   ret_from_fork+0x2d/0x70
   ret_from_fork_asm+0x11/0x20

  Allocated by task 20917:
   kasan_save_stack+0x37/0x60
   kasan_save_track+0x10/0x30
   __kasan_slab_alloc+0x7d/0x80
   kmem_cache_alloc_noprof+0x16e/0x3e0
   mempool_alloc_noprof+0x12e/0x310
   bio_alloc_bioset+0x3f0/0x7a0
   btrfs_bio_alloc+0x2e/0x50 [btrfs]
   submit_extent_page+0x4d1/0xdb0 [btrfs]
   btrfs_do_readpage+0x8b4/0x12a0 [btrfs]
   btrfs_readahead+0x29a/0x430 [btrfs]
   read_pages+0x1a7/0xc60
   page_cache_ra_unbounded+0x2ad/0x560
   filemap_get_pages+0x629/0xa20
   filemap_read+0x335/0xbf0
   vfs_read+0x790/0xcb0
   ksys_read+0xfd/0x1d0
   do_syscall_64+0x6d/0x140
   entry_SYSCALL_64_after_hwframe+0x4b/0x53

  Freed by task 20917:
   kasan_save_stack+0x37/0x60
   kasan_save_track+0x10/0x30
   kasan_save_free_info+0x37/0x50
   __kasan_slab_free+0x4b/0x60
   kmem_cache_free+0x214/0x5d0
   bio_free+0xed/0x180
   end_bbio_data_read+0x1cc/0x580 [btrfs]
   btrfs_submit_chunk+0x98d/0x1880 [btrfs]
   btrfs_submit_bio+0x33/0x70 [btrfs]
   submit_one_bio+0xd4/0x130 [btrfs]
   submit_extent_page+0x3ea/0xdb0 [btrfs]
   btrfs_do_readpage+0x8b4/0x12a0 [btrfs]
   btrfs_readahead+0x29a/0x430 [btrfs]
   read_pages+0x1a7/0xc60
   page_cache_ra_unbounded+0x2ad/0x560
   filemap_get_pages+0x629/0xa20
   filemap_read+0x335/0xbf0
   vfs_read+0x790/0xcb0
   ksys_read+0xfd/0x1d0
   do_syscall_64+0x6d/0x140
   entry_SYSCALL_64_after_hwframe+0x4b/0x53

[CAUSE]
Although I cannot reproduce the error, the report itself is good enough
to pin down the cause.

The call trace is the regular endio workqueue context, but the
free-by-task trace is showing that during btrfs_submit_chunk() we
already hit a critical error, and is calling btrfs_bio_end_io() to error
out.  And the original endio function called bio_put() to free the whole
bio.

This means a double freeing thus causing use-after-free, e.g.:

1. Enter btrfs_submit_bio() with a read bio
   The read bio length is 128K, crossing two 64K stripes.

2. The first run of btrfs_submit_chunk()

2.1 Call btrfs_map_block(), which returns 64K
2.2 Call btrfs_split_bio()
    Now there are two bios, one referring to the first 64K, the other
    referring to the second 64K.
2.3 The first half is submitted.

3. The second run of btrfs_submit_chunk()

3.1 Call btrfs_map_block(), which by somehow failed
    Now we call btrfs_bio_end_io() to handle the error

3.2 btrfs_bio_end_io() calls the original endio function
    Which is end_bbio_data_read(), and it calls bio_put() for the
    original bio.

    Now the original bio is freed.

4. The submitted first 64K bio finished
   Now we call into btrfs_check_read_bio() and tries to advance the bio
   iter.
   But since the original bio (thus its iter) is already freed, we
   trigger the above use-after free.

   And even if the memory is not poisoned/corrupted, we will later call
   the original endio function, causing a double freeing.

[FIX]
Instead of calling btrfs_bio_end_io(), call btrfs_orig_bbio_end_io(),
which has the extra check on split bios and do the proper refcounting
for cloned bios.

Furthermore there is already one extra btrfs_cleanup_bio() call, but
that is duplicated to btrfs_orig_bbio_end_io() call, so remove that
label completely.

Reported-by: David Sterba <[email protected]>
Fixes: 852eee6 ("btrfs: allow btrfs_submit_bio to split bios")
CC: [email protected] # 6.6+
Reviewed-by: Josef Bacik <[email protected]>
Signed-off-by: Qu Wenruo <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

fs/btrfs/bio.c

@@ -668,7 +668,6 @@ static bool btrfs_submit_chunk(struct btrfs_bio *bbio, int mirror_num)
 {
 	struct btrfs_inode *inode = bbio->inode;
 	struct btrfs_fs_info *fs_info = bbio->fs_info;
-	struct btrfs_bio *orig_bbio = bbio;
 	struct bio *bio = &bbio->bio;
 	u64 logical = bio->bi_iter.bi_sector << SECTOR_SHIFT;
 	u64 length = bio->bi_iter.bi_size;
@@ -706,7 +705,7 @@ static bool btrfs_submit_chunk(struct btrfs_bio *bbio, int mirror_num)
 		bbio->saved_iter = bio->bi_iter;
 		ret = btrfs_lookup_bio_sums(bbio);
 		if (ret)
-			goto fail_put_bio;
+			goto fail;
 	}
 
 	if (btrfs_op(bio) == BTRFS_MAP_WRITE) {
@@ -740,26 +739,37 @@ static bool btrfs_submit_chunk(struct btrfs_bio *bbio, int mirror_num)
 
 			ret = btrfs_bio_csum(bbio);
 			if (ret)
-				goto fail_put_bio;
+				goto fail;
 		} else if (use_append ||
 			   (btrfs_is_zoned(fs_info) && inode &&
 			    inode->flags & BTRFS_INODE_NODATASUM)) {
 			ret = btrfs_alloc_dummy_sum(bbio);
 			if (ret)
-				goto fail_put_bio;
+				goto fail;
 		}
 	}
 
 	__btrfs_submit_bio(bio, bioc, &smap, mirror_num);
 done:
 	return map_length == length;
 
-fail_put_bio:
-	if (map_length < length)
-		btrfs_cleanup_bio(bbio);
 fail:
 	btrfs_bio_counter_dec(fs_info);
-	btrfs_bio_end_io(orig_bbio, ret);
+	/*
+	 * We have split the original bbio, now we have to end both the current
+	 * @bbio and remaining one, as the remaining one will never be submitted.
+	 */
+	if (map_length < length) {
+		struct btrfs_bio *remaining = bbio->private;
+
+		ASSERT(bbio->bio.bi_pool == &btrfs_clone_bioset);
+		ASSERT(remaining);
+
+		remaining->bio.bi_status = ret;
+		btrfs_orig_bbio_end_io(remaining);
+	}
+	bbio->bio.bi_status = ret;
+	btrfs_orig_bbio_end_io(bbio);
 	/* Do not submit another chunk */
 	return true;
 }