From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: kernel/signal.c: remove the no longer needed SIGNAL_UNKILLABLE check in complete_signal()
complete_signal() checks SIGNAL_UNKILLABLE before it starts to destroy the
thread group, today this is wrong in many ways.
If nothing else, fatal_signal_pending() should always imply that the whole
thread group (except ->group_exit_task if it is not NULL) is killed, this
check breaks the rule.
After the previous changes we can rely on sig_task_ignored();
sig_fatal(sig) && SIGNAL_UNKILLABLE can only be true if we actually want
to kill this task and sig == SIGKILL OR it is traced and debugger can
intercept the signal.
This should hopefully fix the problem reported by Dmitry. This test-case
static int init(void *arg)
{
for (;;)
pause();
}
int main(void)
{
char stack[16 * 1024];
for (;;) {
int pid = clone(init, stack + sizeof(stack)/2,
CLONE_NEWPID | SIGCHLD, NULL);
assert(pid > 0);
assert(ptrace(PTRACE_ATTACH, pid, 0, 0) == 0);
assert(waitpid(-1, NULL, WSTOPPED) == pid);
assert(ptrace(PTRACE_DETACH, pid, 0, SIGSTOP) == 0);
assert(syscall(__NR_tkill, pid, SIGKILL) == 0);
assert(pid == wait(NULL));
}
}
triggers the WARN_ON_ONCE(!(task->jobctl & JOBCTL_STOP_PENDING)) in
task_participate_group_stop(). do_signal_stop()->signal_group_exit()
checks SIGNAL_GROUP_EXIT and return false, but task_set_jobctl_pending()
checks fatal_signal_pending() and does not set JOBCTL_STOP_PENDING.
And his should fix the minor security problem reported by Kyle,
SECCOMP_RET_TRACE can miss fatal_signal_pending() the same way if the task
is the root of a pid namespace.
Link: http://lkml.kernel.org/r/20171103184246.GD21036@xxxxxxxxxx
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Reported-by: Kyle Huey <me@xxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Tested-by: Kyle Huey <me@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/signal.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff -puN kernel/signal.c~remove-the-no-longer-needed-signal_unkillable-check-in-complete_signal kernel/signal.c
--- a/kernel/signal.c~remove-the-no-longer-needed-signal_unkillable-check-in-complete_signal
+++ a/kernel/signal.c
@@ -931,9 +931,9 @@ static void complete_signal(int sig, str
* 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.
*/
_
--
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