Re: [syzbot] [ntfs3?] KASAN: slab-use-after-free Read in chrdev_open

[Hillf Danton]

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  83a7eefedc9b

--- x/fs/open.c
+++ y/fs/open.c
@@ -952,7 +952,18 @@ static int do_dentry_open(struct file *f
 	if (!open)
 		open = f->f_op->open;
 	if (open) {
+		struct super_block *sb = inode->i_sb;
+
+		error = -EINVAL;
+		for (;;) {
+			int a = atomic_read(&sb->s_active);
+			if (a < 1)
+				goto cleanup_all;
+			if (a == atomic_cmpxchg(&sb->s_active, a, a+1))
+				break;
+		}
 		error = open(inode, f);
+		deactivate_super(sb);
 		if (error)
 			goto cleanup_all;
 	}
--