[PATCH] fs/pidfs: when time ns disabled add check for ioctl

[Edward Adam Davis]

syzbot call pidfd_ioctl() with cmd "PIDFD_GET_TIME_NAMESPACE" and disabled
CONFIG_TIME_NS, since time_ns is NULL, it will make NULL ponter deref in
open_namespace.

Reported-and-tested-by: syzbot+34a0ee986f61f15da35d@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=34a0ee986f61f15da35d
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
 fs/pidfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/pidfs.c b/fs/pidfs.c
index c9cb14181def..fe0ddab48f57 100644
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -168,6 +168,8 @@ static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case PIDFD_GET_TIME_NAMESPACE:
 		get_time_ns(nsp->time_ns);
 		ns_common = to_ns_common(nsp->time_ns);
+		if (!nsp->time_ns)
+			return -EINVAL;
 		break;
 	case PIDFD_GET_TIME_FOR_CHILDREN_NAMESPACE:
 		get_time_ns(nsp->time_ns_for_children);
-- 
2.43.0