Subject: CVE-2022-48869: USB: gadgetfs: Fix race between mounting and unmounting

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

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

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

USB: gadgetfs: Fix race between mounting and unmounting

The syzbot fuzzer and Gerald Lee have identified a use-after-free bug
in the gadgetfs driver, involving processes concurrently mounting and
unmounting the gadgetfs filesystem.  In particular, gadgetfs_fill_super()
can race with gadgetfs_kill_sb(), causing the latter to deallocate
the_device while the former is using it.  The output from KASAN says,
in part:

BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
BUG: KASAN: use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:176 [inline]
BUG: KASAN: use-after-free in __refcount_sub_and_test include/linux/refcount.h:272 [inline]
BUG: KASAN: use-after-free in __refcount_dec_and_test include/linux/refcount.h:315 [inline]
BUG: KASAN: use-after-free in refcount_dec_and_test include/linux/refcount.h:333 [inline]
BUG: KASAN: use-after-free in put_dev drivers/usb/gadget/legacy/inode.c:159 [inline]
BUG: KASAN: use-after-free in gadgetfs_kill_sb+0x33/0x100 drivers/usb/gadget/legacy/inode.c:2086
Write of size 4 at addr ffff8880276d7840 by task syz-executor126/18689

CPU: 0 PID: 18689 Comm: syz-executor126 Not tainted 6.1.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
...
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:176 [inline]
 __refcount_sub_and_test include/linux/refcount.h:272 [inline]
 __refcount_dec_and_test include/linux/refcount.h:315 [inline]
 refcount_dec_and_test include/linux/refcount.h:333 [inline]
 put_dev drivers/usb/gadget/legacy/inode.c:159 [inline]
 gadgetfs_kill_sb+0x33/0x100 drivers/usb/gadget/legacy/inode.c:2086
 deactivate_locked_super+0xa7/0xf0 fs/super.c:332
 vfs_get_super fs/super.c:1190 [inline]
 get_tree_single+0xd0/0x160 fs/super.c:1207
 vfs_get_tree+0x88/0x270 fs/super.c:1531
 vfs_fsconfig_locked fs/fsopen.c:232 [inline]

The simplest solution is to ensure that gadgetfs_fill_super() and
gadgetfs_kill_sb() are serialized by making them both acquire a new
mutex.

The Linux kernel CVE team has assigned CVE-2022-48869 to this issue.

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

	Issue introduced in 5.3 with commit e5d82a7360d1 and fixed in 5.4.230 with commit 9a39f4626b36
	Issue introduced in 5.3 with commit e5d82a7360d1 and fixed in 5.10.165 with commit 856e4b5e53f2
	Issue introduced in 5.3 with commit e5d82a7360d1 and fixed in 5.15.90 with commit a2e075f40122
	Issue introduced in 5.3 with commit e5d82a7360d1 and fixed in 6.1.8 with commit 616fd34d0170
	Issue introduced in 5.3 with commit e5d82a7360d1 and fixed in 6.2 with commit d18dcfe9860e

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-2022-48869
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:
	drivers/usb/gadget/legacy/inode.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/9a39f4626b361ee7aa10fd990401c37ec3b466ae
	https://git.kernel.org/stable/c/856e4b5e53f21edbd15d275dde62228dd94fb2b4
	https://git.kernel.org/stable/c/a2e075f40122d8daf587db126c562a67abd69cf9
	https://git.kernel.org/stable/c/616fd34d017000ecf9097368b13d8a266f4920b3
	https://git.kernel.org/stable/c/d18dcfe9860e842f394e37ba01ca9440ab2178f4