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

From: Greg KH
Date: Fri Sep 24 2010 - 12:56:21 EST


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

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

From: Amit Shah <amit.shah@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
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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