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

kprobes: don't call disarm_kprobe() for disabled kprobes

The assumption in __disable_kprobe() is wrong, and it could try to disarm
an already disarmed kprobe and fire the WARN_ONCE() below. [0] We can
easily reproduce this issue.

1. Write 0 to /sys/kernel/debug/kprobes/enabled.

echo 0 > /sys/kernel/debug/kprobes/enabled

2. Run execsnoop. At this time, one kprobe is disabled.

/usr/share/bcc/tools/execsnoop &

[1] 2460
PCOMM PID PPID RET ARGS

cat /sys/kernel/debug/kprobes/list

ffffffff91345650 r __x64_sys_execve+0x0 [FTRACE]
ffffffff91345650 k __x64_sys_execve+0x0 [DISABLED][FTRACE]

3. Write 1 to /sys/kernel/debug/kprobes/enabled, which changes
   kprobes_all_disarmed to false but does not arm the disabled kprobe.

echo 1 > /sys/kernel/debug/kprobes/enabled

cat /sys/kernel/debug/kprobes/list

ffffffff91345650 r __x64_sys_execve+0x0 [FTRACE]
ffffffff91345650 k __x64_sys_execve+0x0 [DISABLED][FTRACE]

4. Kill execsnoop, when __disable_kprobe() calls disarm_kprobe() for the
   disabled kprobe and hits the WARN_ONCE() in __disarm_kprobe_ftrace().

fg

/usr/share/bcc/tools/execsnoop
^C

Actually, WARN_ONCE() is fired twice, and __unregister_kprobe_top() misses
some cleanups and leaves the aggregated kprobe in the hash table. Then,
__unregister_trace_kprobe() initialises tk->rp.kp.list and creates an
infinite loop like this.

aggregated kprobe.list -> kprobe.list -.
^ |
'.__.'

In this situation, these commands fall into the infinite loop and result
in RCU stall or soft lockup.

cat /sys/kernel/debug/kprobes/list : show_kprobe_addr() enters into the
infinite loop with RCU.

/usr/share/bcc/tools/execsnoop : warn_kprobe_rereg() holds kprobe_mutex,
and __get_valid_kprobe() is stuck in
the loop.

To avoid the issue, make sure we don't call disarm_kprobe() for disabled
kprobes.

[0]
Failed to disarm kprobe-ftrace at __x64_sys_execve+0x0/0x40 (error -2)
WARNING: CPU: 6 PID: 2460 at kernel/kprobes.c:1130 __disarm_kprobe_ftrace.isra.19 (kernel/kprobes.c:1129)
Modules linked in: ena
CPU: 6 PID: 2460 Comm: execsnoop Not tainted 5.19.0+ #28
Hardware name: Amazon EC2 c5.2xlarge/, BIOS 1.0 10/16/2017
RIP: 0010:__disarm_kprobe_ftrace.isra.19 (kernel/kprobes.c:1129)
Code: 24 8b 02 eb c1 80 3d c4 83 f2 01 00 75 d4 48 8b 75 00 89 c2 48 c7 c7 90 fa 0f 92 89 04 24 c6 05 ab 83 01 e8 e4 94 f0 ff <0f> 0b 8b 04 24 eb b1 89 c6 48 c7 c7 60 fa 0f 92 89 04 24 e8 cc 94
RSP: 0018:ffff9e6ec154bd98 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffffffff930f7b00 RCX: 0000000000000001
RDX: 0000000080000001 RSI: ffffffff921461c5 RDI: 00000000ffffffff
RBP: ffff89c504286da8 R08: 0000000000000000 R09: c0000000fffeffff
R10: 0000000000000000 R11: ffff9e6ec154bc28 R12: ffff89c502394e40
R13: ffff89c502394c00 R14: ffff9e6ec154bc00 R15: 0000000000000000
FS: 00007fe800398740(0000) GS:ffff89c812d80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c00057f010 CR3: 0000000103b54006 CR4: 00000000007706e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:

__disable_kprobe (kernel/kprobes.c:1716)
disable_kprobe (kernel/kprobes.c:2392)
__disable_trace_kprobe (kernel/trace/trace_kprobe.c:340)
disable_trace_kprobe (kernel/trace/trace_kprobe.c:429)
perf_trace_event_unreg.isra.2 (./include/linux/tracepoint.h:93 kernel/trace/trace_event_perf.c:168)
perf_kprobe_destroy (kernel/trace/trace_event_perf.c:295)
_free_event (kernel/events/core.c:4971)
perf_event_release_kernel (kernel/events/core.c:5176)
perf_release (kernel/events/core.c:5186)
__fput (fs/file_table.c:321)
task_work_run (./include/linux/
---truncated---

References

• https://nvd.nist.gov/vuln/detail/CVE-2022-50008
• https://git.kernel.org/stable/c/19cd630712e7c13a3dedfc6986a9b983fed6fd98
• https://git.kernel.org/stable/c/55c7a91527343d2e0b5647cc308c6e04ddd2aa52
• https://git.kernel.org/stable/c/6f3c1bc22fc2165461883f506b4d2c3594bd7137
• https://git.kernel.org/stable/c/744b0d3080709a172f0408aedabd1cedd24c2ee6
• https://git.kernel.org/stable/c/9c80e79906b4ca440d09e7f116609262bb747909
• https://git.kernel.org/stable/c/b474ff1b20951f1eac75d100a93861e6da2b522b
• https://git.kernel.org/stable/c/bc3188d8a3b8c08c306a4c851ddb2c92ba4599ca
• https://git.kernel.org/stable/c/fc91d2db55acdaf0c0075b624e572d3520ca3bc3