Commit a7f0765e authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

ptrace: __ptrace_detach: do __wake_up_parent() if we reap the tracee 



The bug is old, it wasn't cause by recent changes.

Test case:

	static void *tfunc(void *arg)
	{
		int pid = (long)arg;

		assert(ptrace(PTRACE_ATTACH, pid, NULL, NULL) == 0);
		kill(pid, SIGKILL);

		sleep(1);
		return NULL;
	}

	int main(void)
	{
		pthread_t th;
		long pid = fork();

		if (!pid)
			pause();

		signal(SIGCHLD, SIG_IGN);
		assert(pthread_create(&th, NULL, tfunc, (void*)pid) == 0);

		int r = waitpid(-1, NULL, __WNOTHREAD);
		printf("waitpid: %d %m\n", r);

		return 0;
	}

Before the patch this program hangs, after this patch waitpid() correctly
fails with errno == -ECHILD.

The problem is, __ptrace_detach() reaps the EXIT_ZOMBIE tracee if its
->real_parent is our sub-thread and we ignore SIGCHLD.  But in this case
we should wake up other threads which can sleep in do_wait().

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Vitaly Mayatskikh <vmayatsk@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1dd3a273

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -2059,6 +2059,7 @@ extern int kill_pgrp(struct pid *pid, int sig, int priv); 
extern int kill_pid(struct pid *pid, int sig, int priv);

extern int kill_proc_info(int, struct siginfo *, pid_t);

extern int do_notify_parent(struct task_struct *, int);

extern void __wake_up_parent(struct task_struct *p, struct task_struct *parent);

extern void force_sig(int, struct task_struct *);

extern void force_sig_specific(int, struct task_struct *);

extern int send_sig(int, struct task_struct *, int);

kernel/exit.c

+5 −0
Original line number Diff line number Diff line
@@ -1575,6 +1575,11 @@ static int ptrace_do_wait(struct wait_opts *wo, struct task_struct *tsk) 
	return 0;

}



void __wake_up_parent(struct task_struct *p, struct task_struct *parent)

{

	wake_up_interruptible_sync(&parent->signal->wait_chldexit);

}



static long do_wait(struct wait_opts *wo)

{

	DECLARE_WAITQUEUE(wait, current);

kernel/ptrace.c

+7 −4
Original line number Diff line number Diff line
@@ -266,9 +266,10 @@ static int ignoring_children(struct sighand_struct *sigh) 
 * or self-reaping.  Do notification now if it would have happened earlier.

 * If it should reap itself, return true.

 *

 * If it's our own child, there is no notification to do.

 * But if our normal children self-reap, then this child

 * was prevented by ptrace and we must reap it now.

 * If it's our own child, there is no notification to do. But if our normal

 * children self-reap, then this child was prevented by ptrace and we must

 * reap it now, in that case we must also wake up sub-threads sleeping in

 * do_wait().

 */

static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)

{
@@ -278,9 +279,11 @@ static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p) 
		if (!task_detached(p) && thread_group_empty(p)) {

			if (!same_thread_group(p->real_parent, tracer))

				do_notify_parent(p, p->exit_signal);

			else if (ignoring_children(tracer->sighand))

			else if (ignoring_children(tracer->sighand)) {

				__wake_up_parent(p, tracer);

				p->exit_signal = -1;

			}

		}

		if (task_detached(p)) {

			/* Mark it as in the process of being reaped. */

			p->exit_state = EXIT_DEAD;

kernel/signal.c

+0 −9
Original line number Diff line number Diff line
@@ -1382,15 +1382,6 @@ ret: 
	return ret;

}



/*

 * Wake up any threads in the parent blocked in wait* syscalls.

 */

static inline void __wake_up_parent(struct task_struct *p,

				    struct task_struct *parent)

{

	wake_up_interruptible_sync(&parent->signal->wait_chldexit);

}



/*

 * Let a parent know about the death of a child.

 * For a stopped/continued status change, use do_notify_parent_cldstop instead.

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