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  master

--- x/fs/open.c
+++ y/fs/open.c
@@ -907,6 +907,7 @@ static int do_dentry_open(struct file *f
 	static const struct file_operations empty_fops = {};
 	struct inode *inode = f->f_path.dentry->d_inode;
 	int error;
+	struct super_block *sb = inode->i_sb;
 
 	path_get(&f->f_path);
 	f->f_inode = inode;
@@ -929,6 +930,7 @@ static int do_dentry_open(struct file *f
 		f->f_mode |= FMODE_WRITER;
 	}
 
+	down_read(&sb->s_umount);
 	/* POSIX.1-2008/SUSv4 Section XSI 2.9.7 */
 	if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode))
 		f->f_mode |= FMODE_ATOMIC_POS;
@@ -956,6 +958,7 @@ static int do_dentry_open(struct file *f
 		if (error)
 			goto cleanup_all;
 	}
+	up_read(&sb->s_umount);
 	f->f_mode |= FMODE_OPENED;
 	if ((f->f_mode & FMODE_READ) &&
 	     likely(f->f_op->read || f->f_op->read_iter))
--