linux-kernel - [26/80] virtio: console: Prevent userspace from submitting NULL buffers

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Date:	Fri, 24 Sep 2010 09:24:14 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Amit Shah <amit.shah@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: [26/80] virtio: console: Prevent userspace from submitting NULL buffers

2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Amit Shah <amit.shah@...hat.com>

commit 65745422a898741ee0e7068ef06624ab06e8aefa upstream.

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@...hat.com>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/char/virtio_console.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -596,6 +596,10 @@ static ssize_t port_fops_write(struct fi
 	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;


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