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Commit dfe16dfa authored by Vitaly Mayatskikh's avatar Vitaly Mayatskikh Committed by Linus Torvalds
Browse files

do_wait: fix sys_waitid()-specific behaviour 



do_wait() checks ->wo_info to figure out who is the caller.  If it's not
NULL the caller should be sys_waitid(), in that case do_wait() fixes up
the retval or zeros ->wo_info, depending on retval from underlying
function.

This is bug: user can pass ->wo_info == NULL and sys_waitid() will return
incorrect value.

man 2 waitid says:

	waitid(): returns 0 on success

Test-case:

	int main(void)
	{
		if (fork())
			assert(waitid(P_ALL, 0, NULL, WEXITED) == 0);

		return 0;
	}

Result:

	Assertion `waitid(P_ALL, 0, ((void *)0), 4) == 0' failed.

Move that code to sys_waitid().

User-visible change: sys_waitid() will return 0 on success, either
infop is set or not.

Note, there's another bug in wait_noreap_copyout() which affects
return value of sys_waitid(). It will be fixed in next patch.

Signed-off-by: default avatarVitaly Mayatskikh <v.mayatskih@gmail.com>
Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b6e763f0

kernel/exit.c

+23 −26
Original line number Diff line number Diff line
@@ -1645,32 +1645,6 @@ static long do_wait(struct wait_opts *wo) 
end:

	__set_current_state(TASK_RUNNING);

	remove_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);



	if (wo->wo_info) {

		struct siginfo __user *infop = wo->wo_info;



		if (retval > 0)

			retval = 0;

		else {

			/*

			 * For a WNOHANG return, clear out all the fields

			 * we would set so the user can easily tell the

			 * difference.

			 */

			if (!retval)

				retval = put_user(0, &infop->si_signo);

			if (!retval)

				retval = put_user(0, &infop->si_errno);

			if (!retval)

				retval = put_user(0, &infop->si_code);

			if (!retval)

				retval = put_user(0, &infop->si_pid);

			if (!retval)

				retval = put_user(0, &infop->si_uid);

			if (!retval)

				retval = put_user(0, &infop->si_status);

		}

	}

	return retval;

}
@@ -1715,6 +1689,29 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *, 
	wo.wo_stat	= NULL;

	wo.wo_rusage	= ru;

	ret = do_wait(&wo);



	if (ret > 0) {

		ret = 0;

	} else if (infop) {

		/*

		 * For a WNOHANG return, clear out all the fields

		 * we would set so the user can easily tell the

		 * difference.

		 */

		if (!ret)

			ret = put_user(0, &infop->si_signo);

		if (!ret)

			ret = put_user(0, &infop->si_errno);

		if (!ret)

			ret = put_user(0, &infop->si_code);

		if (!ret)

			ret = put_user(0, &infop->si_pid);

		if (!ret)

			ret = put_user(0, &infop->si_uid);

		if (!ret)

			ret = put_user(0, &infop->si_status);

	}



	put_pid(pid);



	/* avoid REGPARM breakage on x86: */