Subject: CVE-2024-36979: net: bridge: mst: fix vlan use-after-free

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

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

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

net: bridge: mst: fix vlan use-after-free

syzbot reported a suspicious rcu usage[1] in bridge's mst code. While
fixing it I noticed that nothing prevents a vlan to be freed while
walking the list from the same path (br forward delay timer). Fix the rcu
usage and also make sure we are not accessing freed memory by making
br_mst_vlan_set_state use rcu read lock.

[1]
 WARNING: suspicious RCU usage
 6.9.0-rc6-syzkaller #0 Not tainted
 -----------------------------
 net/bridge/br_private.h:1599 suspicious rcu_dereference_protected() usage!
 ...
 stack backtrace:
 CPU: 1 PID: 8017 Comm: syz-executor.1 Not tainted 6.9.0-rc6-syzkaller #0
 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
 Call Trace:
  <IRQ>
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
  lockdep_rcu_suspicious+0x221/0x340 kernel/locking/lockdep.c:6712
  nbp_vlan_group net/bridge/br_private.h:1599 [inline]
  br_mst_set_state+0x1ea/0x650 net/bridge/br_mst.c:105
  br_set_state+0x28a/0x7b0 net/bridge/br_stp.c:47
  br_forward_delay_timer_expired+0x176/0x440 net/bridge/br_stp_timer.c:88
  call_timer_fn+0x18e/0x650 kernel/time/timer.c:1793
  expire_timers kernel/time/timer.c:1844 [inline]
  __run_timers kernel/time/timer.c:2418 [inline]
  __run_timer_base+0x66a/0x8e0 kernel/time/timer.c:2429
  run_timer_base kernel/time/timer.c:2438 [inline]
  run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2448
  __do_softirq+0x2c6/0x980 kernel/softirq.c:554
  invoke_softirq kernel/softirq.c:428 [inline]
  __irq_exit_rcu+0xf2/0x1c0 kernel/softirq.c:633
  irq_exit_rcu+0x9/0x30 kernel/softirq.c:645
  instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
  sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1043
  </IRQ>
  <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
 RIP: 0010:lock_acquire+0x264/0x550 kernel/locking/lockdep.c:5758
 Code: 2b 00 74 08 4c 89 f7 e8 ba d1 84 00 f6 44 24 61 02 0f 85 85 01 00 00 41 f7 c7 00 02 00 00 74 01 fb 48 c7 44 24 40 0e 36 e0 45 <4b> c7 44 25 00 00 00 00 00 43 c7 44 25 09 00 00 00 00 43 c7 44 25
 RSP: 0018:ffffc90013657100 EFLAGS: 00000206
 RAX: 0000000000000001 RBX: 1ffff920026cae2c RCX: 0000000000000001
 RDX: dffffc0000000000 RSI: ffffffff8bcaca00 RDI: ffffffff8c1eaa60
 RBP: ffffc90013657260 R08: ffffffff92efe507 R09: 1ffffffff25dfca0
 R10: dffffc0000000000 R11: fffffbfff25dfca1 R12: 1ffff920026cae28
 R13: dffffc0000000000 R14: ffffc90013657160 R15: 0000000000000246

The Linux kernel CVE team has assigned CVE-2024-36979 to this issue.

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

	Issue introduced in 5.18 with commit ec7328b59176 and fixed in 6.1.93 with commit 8ca9a750fc71
	Issue introduced in 5.18 with commit ec7328b59176 and fixed in 6.6.33 with commit 4488617e5e99
	Issue introduced in 5.18 with commit ec7328b59176 and fixed in 6.8.12 with commit a2b01e65d9ba
	Issue introduced in 5.18 with commit ec7328b59176 and fixed in 6.9.3 with commit e43dd2b1ec74
	Issue introduced in 5.18 with commit ec7328b59176 and fixed in 6.10 with commit 3a7c1661ae13

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-2024-36979
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:
	net/bridge/br_mst.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/8ca9a750fc711911ef616ceb627d07357b04545e
	https://git.kernel.org/stable/c/4488617e5e995a09abe4d81add5fb165674edb59
	https://git.kernel.org/stable/c/a2b01e65d9ba8af2bb086d3b7288ca53a07249ac
	https://git.kernel.org/stable/c/e43dd2b1ec746e105b7db5f9ad6ef14685a615a4
	https://git.kernel.org/stable/c/3a7c1661ae1383364cd6092d851f5e5da64d476b