proc: mem_release() should check mm != NULL

mem_release() can hit mm == NULL, add the necessary check.

Cc: stable@kernel.org
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9cde9edf9c4d..c3617ea7830b 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -822,8 +822,8 @@ loff_t mem_lseek(struct file *file, loff_t offset, int orig)
 static int mem_release(struct inode *inode, struct file *file)
 {
         struct mm_struct *mm = file->private_data;
-
-        mmput(mm);
+        if (mm)
+                mmput(mm);
         return 0;
 }