On 11/01, Dmitry Vyukov wrote:
>
> On Tue, Oct 31, 2017 at 7:34 PM, Oleg Nesterov <o...@redhat.com> wrote:
> > Hmm. I do not see reproducer in this email...
>
> Ah, sorry. You can see full thread with attachments here:
> https://groups.google.com/forum/#!topic/syzkaller-bugs/EUmYZU4m5gU
Heh. I can't say I enjoyed reading the reproducer ;)
> >> > WARNING: CPU: 0 PID: 1 at kernel/signal.c:340
> >> > task_participate_group_stop+0x1ce/0x230 kernel/signal.c:340
> >> > Kernel panic - not syncing: panic_on_warn set ...
> >> >
> >> > CPU: 0 PID: 1 Comm: init Not tainted 4.13.0-mm1+ #5
> >
> > So this is init process with SIGNAL_UNKILLABLE flag set. And I hope it has
> > the pending SIGKILL, otherwise there is something else.
>From repro.c
line 111 r[8] = syscall(__NR_ptrace, 0x10ul, r[7]);
this is PTRACE_ATTACH
line 115 syscall(__NR_ptrace, 0x4200ul, r[7], 0x40000012ul,
0x100012ul);
this is PTRACE_SETOPTIONS and "data" includes PTRACE_O_EXITKILL.
r[7] is initialized at
line 110 r[7] = *(uint32_t*)0x20f9cffc;
so if it is eq to 1 then it can attach to init and in this case the problem
can be explained by the wrong SIGNAL_UNKILLABLE/SIGKILL logic.
But how *(uint32_t*)0x20f9cffc can be 1 ?
line 108 r[6] = syscall(__NR_fcntl, r[1], 0x10ul, 0x20f9cff8ul);
this is F_GETOWN_EX, addr = 0x20f9cff8 == 0x20f9cffc + 4, so if fcntl()
actually succeeds then r[7] == f_owner_ex->pid.
It _can_ be 1, but the reproducer doesn't work for me. If you can reproduce,
could you try the patch below?
Oleg.
diff --git a/kernel/signal.c b/kernel/signal.c
index 800a18f..7e15b56 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -78,7 +78,7 @@ static int sig_task_ignored(struct task_struct *t, int sig,
bool force)
handler = sig_handler(t, sig);
if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) &&
- handler == SIG_DFL && !force)
+ handler == SIG_DFL && !(force && sig_kernel_only(sig)))
return 1;
return sig_handler_ignored(handler, sig);
@@ -94,13 +94,15 @@ static int sig_ignored(struct task_struct *t, int sig, bool
force)
if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig))
return 0;
- if (!sig_task_ignored(t, sig, force))
- return 0;
-
/*
- * Tracers may want to know about even ignored signals.
+ * Tracers may want to know about even ignored signal unless it
+ * is SIGKILL which can't be reported anyway but can be ignored
+ * by SIGNAL_UNKILLABLE task.
*/
- return !t->ptrace;
+ if (t->ptrace && sig != SIGKILL)
+ return 0;
+
+ return sig_task_ignored(t, sig, force);
}
/*
@@ -929,9 +931,9 @@ static void complete_signal(int sig, struct task_struct *p,
int group)
* then start taking the whole group down immediately.
*/
if (sig_fatal(p, sig) &&
- !(signal->flags & (SIGNAL_UNKILLABLE | SIGNAL_GROUP_EXIT)) &&
+ !(signal->flags & SIGNAL_GROUP_EXIT) &&
!sigismember(&t->real_blocked, sig) &&
- (sig == SIGKILL || !t->ptrace)) {
+ (sig == SIGKILL || !p->ptrace)) {
/*
* This signal will be fatal to the whole group.
*/
