TLDRVuln - Cybersecurity Vulnerabilities Made Simple

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

rcu/kvfree: Fix data-race in __mod_timer / kvfree_call_rcu

KCSAN reports a data race when access the krcp->monitor_work.timer.expires

variable in the schedule_delayed_monitor_work() function:

<snip>

BUG: KCSAN: data-race in __mod_timer / kvfree_call_rcu

read to 0xffff888237d1cce8 of 8 bytes by task 10149 on cpu 1:

schedule_delayed_monitor_work kernel/rcu/tree.c:3520 [inline]

kvfree_call_rcu+0x3b8/0x510 kernel/rcu/tree.c:3839

trie_update_elem+0x47c/0x620 kernel/bpf/lpm_trie.c:441

bpf_map_update_value+0x324/0x350 kernel/bpf/syscall.c:203

generic_map_update_batch+0x401/0x520 kernel/bpf/syscall.c:1849

bpf_map_do_batch+0x28c/0x3f0 kernel/bpf/syscall.c:5143

__sys_bpf+0x2e5/0x7a0

__do_sys_bpf kernel/bpf/syscall.c:5741 [inline]

__se_sys_bpf kernel/bpf/syscall.c:5739 [inline]

__x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5739

x64_sys_call+0x2625/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:322

do_syscall_x64 arch/x86/entry/common.c:52 [inline]

do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83

entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff888237d1cce8 of 8 bytes by task 56 on cpu 0:

__mod_timer+0x578/0x7f0 kernel/time/timer.c:1173

add_timer_global+0x51/0x70 kernel/time/timer.c:1330

__queue_delayed_work+0x127/0x1a0 kernel/workqueue.c:2523

queue_delayed_work_on+0xdf/0x190 kernel/workqueue.c:2552

queue_delayed_work include/linux/workqueue.h:677 [inline]

schedule_delayed_monitor_work kernel/rcu/tree.c:3525 [inline]

kfree_rcu_monitor+0x5e8/0x660 kernel/rcu/tree.c:3643

process_one_work kernel/workqueue.c:3229 [inline]

process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3310

worker_thread+0x51d/0x6f0 kernel/workqueue.c:3391

kthread+0x1d1/0x210 kernel/kthread.c:389

ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147

ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Reported by Kernel Concurrency Sanitizer on:

CPU: 0 UID: 0 PID: 56 Comm: kworker/u8:4 Not tainted 6.12.0-rc2-syzkaller-00050-g5b7c893ed5ed #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024

Workqueue: events_unbound kfree_rcu_monitor

<snip>

kfree_rcu_monitor() rearms the work if a "krcp" has to be still

offloaded and this is done without holding krcp->lock, whereas

the kvfree_call_rcu() holds it.

Fix it by acquiring the "krcp->lock" for kfree_rcu_monitor() so

both functions do not race anymore.