CVE-2024-40981 (Moderate severity, published 2024-07-11)
CVSS score: 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
CWE: CWE-833
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
---truncated---
Statement: Red Hat Enterprise Linux is not vulnerable to this CVE, as it does not affect the versions or configurations of the Linux kernel used in its distributions.
Mitigation: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.