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
@@ -35,6 +35,8 @@
 #include <linux/filelock.h>
 
 #include "internal.h"
+#include "mount.h"
+#include "pnode.h"
 
 int do_truncate(struct mnt_idmap *idmap, struct dentry *dentry,
 		loff_t length, unsigned int time_attrs, struct file *filp)
@@ -952,6 +954,12 @@ static int do_dentry_open(struct file *f
 	if (!open)
 		open = f->f_op->open;
 	if (open) {
+		struct mount *mnt = real_mount(f->f_path.mnt);
+		error = -ENODEV;
+		if (mnt->mnt.mnt_flags & MNT_DOOMED)
+			goto cleanup_all;
+		if (mnt_get_count(mnt) < 2)
+			goto cleanup_all;
 		error = open(inode, f);
 		if (error)
 			goto cleanup_all;
--