Re: [syzbot] [cgroups?] KASAN: slab-use-after-free Read in pressure_write

[Edward Adam Davis]

#syz test

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index e32406d62c0d..f76e2b9452d0 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -348,8 +348,12 @@ static ssize_t kernfs_fop_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 	}
 
 	ops = kernfs_ops(of->kn);
-	if (ops->write)
+	if (ops->write) {
+		struct mutex *mutex;
+		mutex = kernfs_open_file_mutex_lock(of->kn);
 		len = ops->write(of, buf, len, iocb->ki_pos);
+		mutex_unlock(mutex);
+	}
 	else
 		len = -EINVAL;