On 1/6/23 8:44 PM, Stanislav Fomichev wrote:
On Fri, Jan 6, 2023 at 12:48 AM Hao Sun <sunhao.th@xxxxxxxxx> wrote:
The following kernel panic can be triggered when a task with pid=1
attach a prog that attempts to send killing signal to itself, also
see [1] for more details:
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
CPU: 3 PID: 1 Comm: systemd Not tainted 6.1.0-09652-g59fe41b5255f #148
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x100/0x178 lib/dump_stack.c:106
panic+0x2c4/0x60f kernel/panic.c:275
do_exit.cold+0x63/0xe4 kernel/exit.c:789
do_group_exit+0xd4/0x2a0 kernel/exit.c:950
get_signal+0x2460/0x2600 kernel/signal.c:2858
arch_do_signal_or_restart+0x78/0x5d0 arch/x86/kernel/signal.c:306
exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
do_syscall_64+0x44/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd
So skip task with pid=1 in bpf_send_signal_common() to avoid the panic.
[1] https://lore.kernel.org/bpf/20221222043507.33037-1-sunhao.th@xxxxxxxxx
Signed-off-by: Hao Sun <sunhao.th@xxxxxxxxx>
Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
Looks good, agree & applied. These three tests could actually be refactored and also
reused in bpf_probe_write_user() given also the latter should have no business to
mess with pid 1.
kernel/trace/bpf_trace.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 23ce498bca97..ed21ab9fe846 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -844,6 +844,9 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type)
*/
if (unlikely(current->flags & (PF_KTHREAD | PF_EXITING)))
return -EPERM;
+ /* Task should not be pid=1 to avoid kernel panic. */
+ if (unlikely(is_global_init(current)))
+ return -EPERM;
if (unlikely(!nmi_uaccess_okay()))
return -EPERM;
base-commit: 4aea86b4033f92f01547e6d4388d4451ae9b0980
--
2.39.0
