From: Amit Shah <amit.shah@redhat.com>
Date: Tue, 14 Sep 2010 07:56:16 +0000 (+0530)
Subject: virtio: console: Prevent userspace from submitting NULL buffers
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=65745422a898741ee0e7068ef06624ab06e8aefa;p=linux-beck.git

virtio: console: Prevent userspace from submitting NULL buffers

A userspace could submit a buffer with 0 length to be written to the
host.  Prevent such a situation.

This was not needed previously, but recent changes in the way write()
works exposed this condition to trigger a virtqueue event to the host,
causing a NULL buffer to be sent across.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
CC: stable@kernel.org
---

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 2f2e31b58b34..c810481a5bc2 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -596,6 +596,10 @@ static ssize_t port_fops_write(struct file *filp, const char __user *ubuf,
 	ssize_t ret;
 	bool nonblock;
 
+	/* Userspace could be out to fool us */
+	if (!count)
+		return 0;
+
 	port = filp->private_data;
 
 	nonblock = filp->f_flags & O_NONBLOCK;