Subject: CVE-2022-48969: xen-netfront: Fix NULL sring after live migration

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

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

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

xen-netfront: Fix NULL sring after live migration

A NAPI is setup for each network sring to poll data to kernel
The sring with source host is destroyed before live migration and
new sring with target host is setup after live migration.
The NAPI for the old sring is not deleted until setup new sring
with target host after migration. With busy_poll/busy_read enabled,
the NAPI can be polled before got deleted when resume VM.

BUG: unable to handle kernel NULL pointer dereference at
0000000000000008
IP: xennet_poll+0xae/0xd20
PGD 0 P4D 0
Oops: 0000 [#1] SMP PTI
Call Trace:
 finish_task_switch+0x71/0x230
 timerqueue_del+0x1d/0x40
 hrtimer_try_to_cancel+0xb5/0x110
 xennet_alloc_rx_buffers+0x2a0/0x2a0
 napi_busy_loop+0xdb/0x270
 sock_poll+0x87/0x90
 do_sys_poll+0x26f/0x580
 tracing_map_insert+0x1d4/0x2f0
 event_hist_trigger+0x14a/0x260

 finish_task_switch+0x71/0x230
 __schedule+0x256/0x890
 recalc_sigpending+0x1b/0x50
 xen_sched_clock+0x15/0x20
 __rb_reserve_next+0x12d/0x140
 ring_buffer_lock_reserve+0x123/0x3d0
 event_triggers_call+0x87/0xb0
 trace_event_buffer_commit+0x1c4/0x210
 xen_clocksource_get_cycles+0x15/0x20
 ktime_get_ts64+0x51/0xf0
 SyS_ppoll+0x160/0x1a0
 SyS_ppoll+0x160/0x1a0
 do_syscall_64+0x73/0x130
 entry_SYSCALL_64_after_hwframe+0x41/0xa6
...
RIP: xennet_poll+0xae/0xd20 RSP: ffffb4f041933900
CR2: 0000000000000008
---[ end trace f8601785b354351c ]---

xen frontend should remove the NAPIs for the old srings before live
migration as the bond srings are destroyed

There is a tiny window between the srings are set to NULL and
the NAPIs are disabled, It is safe as the NAPI threads are still
frozen at that time

The Linux kernel CVE team has assigned CVE-2022-48969 to this issue.

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

	Issue introduced in 2.6.24 with commit 4ec2411980d0 and fixed in 4.19.269 with commit 99859947517e
	Issue introduced in 2.6.24 with commit 4ec2411980d0 and fixed in 5.4.227 with commit ed773dd798bf
	Issue introduced in 2.6.24 with commit 4ec2411980d0 and fixed in 5.10.159 with commit e6860c889f4a
	Issue introduced in 2.6.24 with commit 4ec2411980d0 and fixed in 5.15.83 with commit e6e897d4fe2f
	Issue introduced in 2.6.24 with commit 4ec2411980d0 and fixed in 6.0.13 with commit f2dd60fd3fe9
	Issue introduced in 2.6.24 with commit 4ec2411980d0 and fixed in 6.1 with commit d50b7914fae0

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-2022-48969
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/net/xen-netfront.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/99859947517e446058ad7243ee81d2f9801fa3dd
	https://git.kernel.org/stable/c/ed773dd798bf720756d20021b8d8a4a3d7184bda
	https://git.kernel.org/stable/c/e6860c889f4ad50b6ab696f5ea154295d72cf27a
	https://git.kernel.org/stable/c/e6e897d4fe2f89c0bd94600a40bedf5e6e75e050
	https://git.kernel.org/stable/c/f2dd60fd3fe98bd36a91b0c6e10bfe9d66258f84
	https://git.kernel.org/stable/c/d50b7914fae04d840ce36491d22133070b18cca9