Message-ID: <2024091338-CVE-2024-46687-5668@gregkh>
Date: Fri, 13 Sep 2024 07:30:48 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-46687: btrfs: fix a use-after-free when hitting errors inside btrfs_submit_chunk()

Description
===========

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

btrfs: fix a use-after-free when hitting errors inside btrfs_submit_chunk()

[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+ #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.

The Linux kernel CVE team has assigned CVE-2024-46687 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.3 with commit 852eee62d31a and fixed in 6.6.49 with commit 51722b99f41f
	Issue introduced in 6.3 with commit 852eee62d31a and fixed in 6.10.8 with commit 4a3b9e1a8e6c
	Issue introduced in 6.3 with commit 852eee62d31a and fixed in 6.11-rc6 with commit 10d9d8c3512f

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-46687
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/btrfs/bio.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/51722b99f41f5e722ffa10b8f61e802a0e70b331
	https://git.kernel.org/stable/c/4a3b9e1a8e6cd1a8d427a905e159de58d38941cc
	https://git.kernel.org/stable/c/10d9d8c3512f16cad47b2ff81ec6fc4b27d8ee10

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