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

[Hillf Danton]

On Fri, 26 Apr 2024 05:00:21 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    e33c4963bf53 Merge tag 'nfsd-6.9-5' of git://git.kernel.or..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12499380980000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  e33c4963bf53

--- x/fs/char_dev.c
+++ y/fs/char_dev.c
@@ -387,6 +387,8 @@ static int chrdev_open(struct inode *ino
 		if (!kobj)
 			return -ENXIO;
 		new = container_of(kobj, struct cdev, kobj);
+		if (!cdev_get(new))
+			return -ENXIO;
 		spin_lock(&cdev_lock);
 		/* Check i_cdev again in case somebody beat us to it while
 		   we dropped the lock. */
--