[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@xxxxxxxxx>
Reviewed-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
 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

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