On Fri, Jan 06, 2023 at 02:18:38PM IST, Hao Sun 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> > --- > 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; Sorry for chiming in late. This seems a bit too restrictive, there are a lot of legitimate signals that can be sent to the init process (like the ones listed in man 1 systemd). Maybe you should only prevent sig == SIGKILL and not others?
