Sorry for delay, I was offline. I'll try to return to this problem next
week, currently I can't even read this thread but at first glance the
proposed patch(es) do not look right...
On 09/21, Michal Hocko wrote:
>
> The further investigation shown that the tracer (strace) is stuck
> waiting for cred_guard_mutex
> [<0000000000000000>] mm_access+0x22/0xa0
> [<0000000000000000>] process_vm_rw_core.isra.1+0x112/0x6c0
> [<0000000000000000>] process_vm_rw+0xab/0x110
> [<0000000000000000>] SyS_process_vm_readv+0x15/0x20
> [<0000000000000000>] system_call_fastpath+0x16/0x1b
> [<0000000000000000>] 0x7f186f031c3a
> [<0000000000000000>] 0xffffffffffffffff
...
> this however doesn't happen because both threads which are dead
> are zombies waiting to be reaped by the parent and to call their
> release_task->__exit_signal.
Yes, I know, this was already reported. And so far I do not see any
reasonable fix. I _think_ that the "real" fix should rework the
security_bprm_* helpers, but unlikely this is possible.
The trivial test-case:
void *thread(void *arg)
{
ptrace(PTRACE_TRACEME, 0,0,0);
return NULL;
}
int main(void)
{
int pid = fork();
if (!pid) {
pthread_t pt;
pthread_create(&pt, NULL, thread, NULL);
pthread_join(pt, NULL);
execlp("echo", "echo", "passed", NULL);
}
sleep(1);
// or anything else which needs ->cred_guard_mutex,
// say open(/proc/$pid/mem)
ptrace(PTRACE_ATTACH, pid, 0,0);
kill(pid, SIGCONT);
return 0;
}
Oleg.
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