Subject: CVE-2022-48733: btrfs: fix use-after-free after failure to create a snapshot

From: Greg Kroah-Hartman <[email-masked]>

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

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

btrfs: fix use-after-free after failure to create a snapshot

At ioctl.c:create_snapshot(), we allocate a pending snapshot structure and
then attach it to the transaction's list of pending snapshots. After that
we call btrfs_commit_transaction(), and if that returns an error we jump
to 'fail' label, where we kfree() the pending snapshot structure. This can
result in a later use-after-free of the pending snapshot:

1) We allocated the pending snapshot and added it to the transaction's
   list of pending snapshots;

2) We call btrfs_commit_transaction(), and it fails either at the first
   call to btrfs_run_delayed_refs() or btrfs_start_dirty_block_groups().
   In both cases, we don't abort the transaction and we release our
   transaction handle. We jump to the 'fail' label and free the pending
   snapshot structure. We return with the pending snapshot still in the
   transaction's list;

3) Another task commits the transaction. This time there's no error at
   all, and then during the transaction commit it accesses a pointer
   to the pending snapshot structure that the snapshot creation task
   has already freed, resulting in a user-after-free.

This issue could actually be detected by smatch, which produced the
following warning:

  fs/btrfs/ioctl.c:843 create_snapshot() warn: '&pending_snapshot->list' not removed from list

So fix this by not having the snapshot creation ioctl directly add the
pending snapshot to the transaction's list. Instead add the pending
snapshot to the transaction handle, and then at btrfs_commit_transaction()
we add the snapshot to the list only when we can guarantee that any error
returned after that point will result in a transaction abort, in which
case the ioctl code can safely free the pending snapshot and no one can
access it anymore.

The Linux kernel CVE team has assigned CVE-2022-48733 to this issue.

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

	Fixed in 5.10.226 with commit 7e4c72dbaf62
	Fixed in 5.15.22 with commit a7b717fa1516
	Fixed in 5.16.8 with commit 9372fa1d73da
	Fixed in 5.17 with commit 28b21c558a37

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-2022-48733
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/ioctl.c
	fs/btrfs/transaction.c
	fs/btrfs/transaction.h

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/7e4c72dbaf62f8978af8321a24dbd35566d3a78a
	https://git.kernel.org/stable/c/a7b717fa15165d3d9245614680bebc48a52ac05d
	https://git.kernel.org/stable/c/9372fa1d73da5f1673921e365d0cd2c27ec7adc2
	https://git.kernel.org/stable/c/28b21c558a3753171097193b6f6602a94169093a