[PATCH 0/2] sys_waitid() fixes

[PATCH 0/2] sys_waitid() fixes

[Vitaly Mayatskikh]

These patches applied on top of Oleg's work in -mm (but don't interfere
with it):

do_wait-wakeup-optimization-shift-security_task_wait-from-eligible_child-to-wait_consider_task.patch
do_wait-wakeup-optimization-change-__wake_up_parent-to-use-filtered-wakeup.patch
do_wait-wakeup-optimization-child_wait_callback-check-__wnothread-case.patch
do_wait-optimization-do-not-place-sub-threads-on-task_struct-children-list.patch
wait_consider_task-kill-parent-argument.patch

Vitaly Mayatskikh (2):
  do_wait: fix sys_waitid()-specific behaviour
  Check for ->wo_info != NULL in wait_noreap_copyout()

 kernel/exit.c |   75 ++++++++++++++++++++++++++++-----------------------------
 1 files changed, 37 insertions(+), 38 deletions(-)

[PATCH 1/2] do_wait: fix sys_waitid()-specific behaviour

[Vitaly Mayatskikh]

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.

>From man 2 waitid:

	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: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/exit.c |   49 +++++++++++++++++++++++--------------------------
 1 files changed, 23 insertions(+), 26 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 80a15b6..62e3646 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1630,32 +1630,6 @@ notask:
 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;
 }
 
@@ -1700,6 +1674,29 @@ 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: */
-- 
1.6.2.5

[PATCH 2/2] Check for ->wo_info != NULL in wait_noreap_copyout()

[Vitaly Mayatskikh]

Current behaviour of sys_waitid() looks odd. If user passes infop == NULL,
sys_waitid() returns success. When user additionally specifies flag WNOWAIT,
sys_waitid() returns -EFAULT on the same conditions. When user combines
WNOWAIT with WCONTINUED, sys_waitid() again returns success.

This patch adds check for ->wo_info in wait_noreap_copyout().

User-visible change: starting from this commit, sys_waitid() always checks
infop != NULL and does not fail if it is NULL.

Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/exit.c |   26 ++++++++++++++------------
 1 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 62e3646..f306f20 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1134,18 +1134,20 @@ static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
 
 	put_task_struct(p);
 	infop = wo->wo_info;
-	if (!retval)
-		retval = put_user(SIGCHLD, &infop->si_signo);
-	if (!retval)
-		retval = put_user(0, &infop->si_errno);
-	if (!retval)
-		retval = put_user((short)why, &infop->si_code);
-	if (!retval)
-		retval = put_user(pid, &infop->si_pid);
-	if (!retval)
-		retval = put_user(uid, &infop->si_uid);
-	if (!retval)
-		retval = put_user(status, &infop->si_status);
+	if (infop) {
+		if (!retval)
+			retval = put_user(SIGCHLD, &infop->si_signo);
+		if (!retval)
+			retval = put_user(0, &infop->si_errno);
+		if (!retval)
+			retval = put_user((short)why, &infop->si_code);
+		if (!retval)
+			retval = put_user(pid, &infop->si_pid);
+		if (!retval)
+			retval = put_user(uid, &infop->si_uid);
+		if (!retval)
+			retval = put_user(status, &infop->si_status);
+	}
 	if (!retval)
 		retval = pid;
 	return retval;
-- 
1.6.2.5