Subject: CVE-2024-40981: batman-adv: bypass empty buckets in batadv_purge_orig_ref()

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

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

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

batman-adv: bypass empty buckets in batadv_purge_orig_ref()

Many syzbot reports are pointing to soft lockups in
batadv_purge_orig_ref() [1]

Root cause is unknown, but we can avoid spending too much
time there and perhaps get more interesting reports.

[1]

watchdog: BUG: soft lockup - CPU#0 stuck for 27s! [kworker/u4:6:621]
Modules linked in:
irq event stamp: 6182794
 hardirqs last  enabled at (6182793): [<ffff8000801dae10>] __local_bh_enable_ip+0x224/0x44c kernel/softirq.c:386
 hardirqs last disabled at (6182794): [<ffff80008ad66a78>] __el1_irq arch/arm64/kernel/entry-common.c:533 [inline]
 hardirqs last disabled at (6182794): [<ffff80008ad66a78>] el1_interrupt+0x24/0x68 arch/arm64/kernel/entry-common.c:551
 softirqs last  enabled at (6182792): [<ffff80008aab71c4>] spin_unlock_bh include/linux/spinlock.h:396 [inline]
 softirqs last  enabled at (6182792): [<ffff80008aab71c4>] batadv_purge_orig_ref+0x114c/0x1228 net/batman-adv/originator.c:1287
 softirqs last disabled at (6182790): [<ffff80008aab61dc>] spin_lock_bh include/linux/spinlock.h:356 [inline]
 softirqs last disabled at (6182790): [<ffff80008aab61dc>] batadv_purge_orig_ref+0x164/0x1228 net/batman-adv/originator.c:1271
CPU: 0 PID: 621 Comm: kworker/u4:6 Not tainted 6.8.0-rc7-syzkaller-g707081b61156 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
Workqueue: bat_events batadv_purge_orig
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : should_resched arch/arm64/include/asm/preempt.h:79 [inline]
 pc : __local_bh_enable_ip+0x228/0x44c kernel/softirq.c:388
 lr : __local_bh_enable_ip+0x224/0x44c kernel/softirq.c:386
sp : ffff800099007970
x29: ffff800099007980 x28: 1fffe00018fce1bd x27: dfff800000000000
x26: ffff0000d2620008 x25: ffff0000c7e70de8 x24: 0000000000000001
x23: 1fffe00018e57781 x22: dfff800000000000 x21: ffff80008aab71c4
x20: ffff0001b40136c0 x19: ffff0000c72bbc08 x18: 1fffe0001a817bb0
x17: ffff800125414000 x16: ffff80008032116c x15: 0000000000000001
x14: 1fffe0001ee9d610 x13: 0000000000000000 x12: 0000000000000003
x11: 0000000000000000 x10: 0000000000ff0100 x9 : 0000000000000000
x8 : 00000000005e5789 x7 : ffff80008aab61dc x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000000
x2 : 0000000000000006 x1 : 0000000000000080 x0 : ffff800125414000
Call trace:
  __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:27 [inline]
  arch_local_irq_enable arch/arm64/include/asm/irqflags.h:49 [inline]
  __local_bh_enable_ip+0x228/0x44c kernel/softirq.c:386
  __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline]
  _raw_spin_unlock_bh+0x3c/0x4c kernel/locking/spinlock.c:210
  spin_unlock_bh include/linux/spinlock.h:396 [inline]
  batadv_purge_orig_ref+0x114c/0x1228 net/batman-adv/originator.c:1287
  batadv_purge_orig+0x20/0x70 net/batman-adv/originator.c:1300
  process_one_work+0x694/0x1204 kernel/workqueue.c:2633
  process_scheduled_works kernel/workqueue.c:2706 [inline]
  worker_thread+0x938/0xef4 kernel/workqueue.c:2787
  kthread+0x288/0x310 kernel/kthread.c:388
  ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.8.0-rc7-syzkaller-g707081b61156 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : arch_local_irq_enable+0x8/0xc arch/arm64/include/asm/irqflags.h:51
 lr : default_idle_call+0xf8/0x128 kernel/sched/idle.c:103
sp : ffff800093a17d30
x29: ffff800093a17d30 x28: dfff800000000000 x27: 1ffff00012742fb4
x26: ffff80008ec9d000 x25: 0000000000000000 x24: 0000000000000002
x23: 1ffff00011d93a74 x22: ffff80008ec9d3a0 x21: 0000000000000000
x20: ffff0000c19dbc00 x19: ffff8000802d0fd8 x18: 1fffe00036804396
x17: ffff80008ec9d000 x16: ffff8000802d089c x15: 0000000000000001
x14: 1fffe00036805f10 x13: 0000000000000000 x12: 0000000000000003
x11: 0000000000000001 x10: 0000000000000003 x9 : 0000000000000000
x8 : 00000000000ce8d1 x7 : ffff8000804609e4 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000001 x3 : ffff80008ad6aac0
x2 : 0000000000000000 x1 : ffff80008aedea60 x0 : ffff800125436000
Call trace:
  __daif_local_irq_enable arch/arm64/include/asm/irqflags.h:27 [inline]
  arch_local_irq_enable+0x8/0xc arch/arm64/include/asm/irqflags.h:49
  cpuidle_idle_call kernel/sched/idle.c:170 [inline]
  do_idle+0x1f0/0x4e8 kernel/sched/idle.c:312
  cpu_startup_entry+0x5c/0x74 kernel/sched/idle.c:410
  secondary_start_kernel+0x198/0x1c0 arch/arm64/kernel/smp.c:272
  __secondary_switched+0xb8/0xbc arch/arm64/kernel/head.S:404

The Linux kernel CVE team has assigned CVE-2024-40981 to this issue.

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

	Fixed in 4.19.317 with commit 79636f636126
	Fixed in 5.4.279 with commit 154e3f862ba3
	Fixed in 5.10.221 with commit 82cdea8f3af1
	Fixed in 5.15.162 with commit 92176caf9896
	Fixed in 6.1.96 with commit fed7914858a1
	Fixed in 6.6.36 with commit 2685008a5f9a
	Fixed in 6.9.7 with commit ae7f3cffe86a
	Fixed in 6.10 with commit 40dc8ab60589

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-2024-40981
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/batman-adv/originator.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/79636f636126775436a11ee9cf00a9253a33ac11
	https://git.kernel.org/stable/c/154e3f862ba33675cf3f4abf0a0a309a89df87d2
	https://git.kernel.org/stable/c/82cdea8f3af1e36543c937df963d108c60bea030
	https://git.kernel.org/stable/c/92176caf9896572f00e741a93cecc0ef1172da07
	https://git.kernel.org/stable/c/fed7914858a1f1f3e6350bb0f620d6ef15107d16
	https://git.kernel.org/stable/c/2685008a5f9a636434a8508419cee8158a2f52c8
	https://git.kernel.org/stable/c/ae7f3cffe86aea3da0e8e079525a1ae619b8862a
	https://git.kernel.org/stable/c/40dc8ab605894acae1473e434944924a22cfaaa0