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signal: Restore the stop PTRACE_EVENT_EXIT 

commit cf43a757fd49442bc38f76088b70c2299eed2c2f upstream.

In the middle of do_exit() there is there is a call
"ptrace_event(PTRACE_EVENT_EXIT, code);" That call places the process
in TACKED_TRACED aka "(TASK_WAKEKILL | __TASK_TRACED)" and waits for
for the debugger to release the task or SIGKILL to be delivered.

Skipping past dequeue_signal when we know a fatal signal has already
been delivered resulted in SIGKILL remaining pending and
TIF_SIGPENDING remaining set.  This in turn caused the
scheduler to not sleep in PTACE_EVENT_EXIT as it figured
a fatal signal was pending.  This also caused ptrace_freeze_traced
in ptrace_check_attach to fail because it left a per thread
SIGKILL pending which is what fatal_signal_pending tests for.

This difference in signal state caused strace to report
strace: Exit of unknown pid NNNNN ignored

Therefore update the signal handling state like dequeue_signal
would when removing a per thread SIGKILL, by removing SIGKILL
from the per thread signal mask and clearing TIF_SIGPENDING.

Acked-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Ivan Delalande <colona@arista.com>
Fixes: 35634ffa1751 ("signal: Always notice exiting tasks")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Eric W. Biederman 2019-02-11 23:27:42 -06:00 committed by syphyr
parent 0554234e36
commit 031a63b7a3
1 changed files with 5 additions and 2 deletions
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7
kernel/signal.c
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@ -2272,9 +2272,12 @@ relock:
}
/* Has this task already been marked for death? */
ksig->info.si_signo = signr = SIGKILL;
if (signal_group_exit(signal))
if (signal_group_exit(signal)) {
ksig->info.si_signo = signr = SIGKILL;
sigdelset(&current->pending.signal, SIGKILL);
recalc_sigpending();
goto fatal;
}
for (;;) {
struct k_sigaction *ka;