[RFC 1/2] proc: Return if nothing to unmount

[Gargi Sharma]

If a task exits before procfs is mounted, proc_flush_task_mnt will
be called with a NULL mnt parameter. In that case, not only is there
nothing to unhash, but trying to do so will oops the kernel with a
null pointer dereference.

Signed-off-by: Gargi Sharma <gs051095@xxxxxxxxx>
---
 fs/proc/base.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index e5d89a0..7b83c21 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3021,6 +3021,10 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid)
 	char buf[PROC_NUMBUF];
 	struct qstr name;
 
+	/* procfs is not mounted. There is nothing to unhash. */
+	if (!mnt)
+		return;
+
 	name.name = buf;
 	name.len = snprintf(buf, sizeof(buf), "%d", pid);
 	/* no ->d_hash() rejects on procfs */
-- 
2.7.4