In the Linux kernel, the following vulnerability has been resolved:

btrfs: scrub: avoid use-after-free when chunk length is not 64K aligned

[BUG]
There is a bug report that, on a ext4-converted btrfs, scrub leads to
various problems, including:

• “unable to find chunk map” errors
  BTRFS info (device vdb): scrub: started on devid 1
  BTRFS critical (device vdb): unable to find chunk map for logical 2214744064 length 4096
  BTRFS critical (device vdb): unable to find chunk map for logical 2214744064 length 45056
  

This would lead to unrepariable errors.

• Use-after-free KASAN reports:

  BUG: KASAN: slab-use-after-free in __blk_rq_map_sg+0x18f/0x7c0
  Read of size 8 at addr ffff8881013c9040 by task btrfs/909
  CPU: 0 PID: 909 Comm: btrfs Not tainted 6.7.0-x64v3-dbg #11 c50636e9419a8354555555245df535e380563b2b
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 2023.11-2 12/24/2023
  Call Trace:
  <TASK>
  dump_stack_lvl+0x43/0x60
  print_report+0xcf/0x640
  kasan_report+0xa6/0xd0
  __blk_rq_map_sg+0x18f/0x7c0
  virtblk_prep_rq.isra.0+0x215/0x6a0 [virtio_blk 19a65eeee9ae6fcf02edfad39bb9ddee07dcdaff]
  virtio_queue_rqs+0xc4/0x310 [virtio_blk 19a65eeee9ae6fcf02edfad39bb9ddee07dcdaff]
  blk_mq_flush_plug_list.part.0+0x780/0x860
  __blk_flush_plug+0x1ba/0x220
  blk_finish_plug+0x3b/0x60
  submit_initial_group_read+0x10a/0x290 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
  flush_scrub_stripes+0x38e/0x430 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
  scrub_stripe+0x82a/0xae0 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
  scrub_chunk+0x178/0x200 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
  scrub_enumerate_chunks+0x4bc/0xa30 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
  btrfs_scrub_dev+0x398/0x810 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
  btrfs_ioctl+0x4b9/0x3020 [btrfs e57987a360bed82fe8756dcd3e0de5406ccfe965]
  __x64_sys_ioctl+0xbd/0x100
  do_syscall_64+0x5d/0xe0
  entry_SYSCALL_64_after_hwframe+0x63/0x6b
  RIP: 0033:0x7f47e5e0952b

• Crash, mostly due to above use-after-free

[CAUSE]
The converted fs has the following data chunk layout:

item 2 key (FIRST_CHUNK_TREE CHUNK_ITEM 2214658048) itemoff 16025 itemsize 80
    length 86016 owner 2 stripe_len 65536 type DATA|single

For above logical bytenr 2214744064, it’s at the chunk end
(2214658048 + 86016 = 2214744064).

This means btrfs_submit_bio() would split the bio, and trigger endio
function for both of the two halves.

However scrub_submit_initial_read() would only expect the endio function
to be called once, not any more.
This means the first endio function would already free the bbio::bio,
leaving the bvec freed, thus the 2nd endio call would lead to
use-after-free.

[FIX]

• Make sure scrub_read_endio() only updates bits in its range
  Since we may read less than 64K at the end of the chunk, we should not
  touch the bits beyond chunk boundary.

• Make sure scrub_submit_initial_read() only to read the chunk range
  This is done by calculating the real number of sectors we need to
  read, and add sector-by-sector to the bio.

Thankfully the scrub read repair path won’t need extra fixes:

• scrub_stripe_submit_repair_read()
  With above fixes, we won’t update error bit for range beyond chunk,
  thus scrub_stripe_submit_repair_read() should never submit any read
  beyond the chunk.