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ptrace: dont send SIGSTOP on auto-attach if PT_SEIZED

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The fake SIGSTOP during attach has numerous problems. PTRACE_SEIZE
is already fine, but we have basically the same problems is SIGSTOP
is sent on auto-attach, the tracer can't know if this signal signal
should be cancelled or not.

Change ptrace_event() to set JOBCTL_TRAP_STOP if the new child is
PT_SEIZED, this triggers the PTRACE_EVENT_STOP report.

Thereafter a PT_SEIZED task can never report the bogus SIGSTOP.

Test-case:

	#define PTRACE_SEIZE		0x4206
	#define PTRACE_SEIZE_DEVEL	0x80000000
	#define PTRACE_EVENT_STOP	7
	#define WEVENT(s)		((s & 0xFF0000) >> 16)

	int main(void)
	{
		int child, grand_child, status;
		long message;

		child = fork();
		if (!child) {
			kill(getpid(), SIGSTOP);
			fork();
			assert(0);
			return 0x23;
		}

		assert(ptrace(PTRACE_SEIZE, child, 0,PTRACE_SEIZE_DEVEL) == 0);
		assert(wait(&status) == child);
		assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);

		assert(ptrace(PTRACE_SETOPTIONS, child, 0, PTRACE_O_TRACEFORK) == 0);

		assert(ptrace(PTRACE_CONT, child, 0,0) == 0);
		assert(waitpid(child, &status, 0) == child);
		assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGTRAP);
		assert(WEVENT(status) == PTRACE_EVENT_FORK);

		assert(ptrace(PTRACE_GETEVENTMSG, child, 0, &message) == 0);
		grand_child = message;

		assert(waitpid(grand_child, &status, 0) == grand_child);
		assert(WIFSTOPPED(status) && WSTOPSIG(status) == SIGTRAP);
		assert(WEVENT(status) == PTRACE_EVENT_STOP);

		kill(child, SIGKILL);
		kill(grand_child, SIGKILL);
		return 0;
	}

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Oleg Nesterov 2011-07-08 19:14:17 +02:00
parent dcace06cc2
commit d184d6eb1d
1 changed files with 5 additions and 1 deletions
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6
include/linux/ptrace.h
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@ -228,7 +228,11 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
child->ptrace = current->ptrace;
__ptrace_link(child, current->parent);
sigaddset(&child->pending.signal, SIGSTOP);
if (child->ptrace & PT_SEIZED)
task_set_jobctl_pending(child, JOBCTL_TRAP_STOP);
else
sigaddset(&child->pending.signal, SIGSTOP);
set_tsk_thread_flag(child, TIF_SIGPENDING);
}
}