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>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9cde9ed..c3617ea 100644 (file)
--- 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;
 }