virtio: console: Prevent userspace from submitting NULL buffers

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@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 942a9826bd23ed64b83095fcdeb65ed059c9ce02..56ffd0d93e253ecc46c474f2b220e57a1e5a90c8 100644 (file)
--- 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;