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

[Hillf Danton <hdanton@sina.com>]

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
@@ -377,6 +377,9 @@ static int chrdev_open(struct inode *ino
 	struct cdev *new = NULL;
 	int ret = 0;
 
+	if (!igrab(inode))
+		return -ENXIO;
+
 	spin_lock(&cdev_lock);
 	p = inode->i_cdev;
 	if (!p) {
@@ -384,8 +387,10 @@ static int chrdev_open(struct inode *ino
 		int idx;
 		spin_unlock(&cdev_lock);
 		kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
-		if (!kobj)
+		if (!kobj) {
+			iput(inode);
 			return -ENXIO;
+		}
 		new = container_of(kobj, struct cdev, kobj);
 		spin_lock(&cdev_lock);
 		/* Check i_cdev again in case somebody beat us to it while
@@ -401,8 +406,10 @@ static int chrdev_open(struct inode *ino
 		ret = -ENXIO;
 	spin_unlock(&cdev_lock);
 	cdev_put(new);
-	if (ret)
+	if (ret) {
+		iput(inode);
 		return ret;
+	}
 
 	ret = -ENXIO;
 	fops = fops_get(p->ops);
@@ -416,10 +423,12 @@ static int chrdev_open(struct inode *ino
 			goto out_cdev_put;
 	}
 
+	iput(inode);
 	return 0;
 
  out_cdev_put:
 	cdev_put(p);
+	iput(inode);
 	return ret;
 }
 
--