macvtap: fix uninitialized access on TUNSETIFF

flags field in ifreq is only 16 bit wide, but
we read it as a 32 bit value.
If userspace doesn't zero-initialize unused fields,
this will lead to failures.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 60f7ee5..80fdb82 100644 (file)
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -999,7 +999,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
        void __user *argp = (void __user *)arg;
        struct ifreq __user *ifr = argp;
        unsigned int __user *up = argp;
-       unsigned int u;
+       unsigned short u;
        int __user *sp = argp;
        int s;
        int ret;
@@ -1014,7 +1014,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
                if ((u & ~MACVTAP_FEATURES) != (IFF_NO_PI | IFF_TAP))
                        ret = -EINVAL;
                else
-                       q->flags = u;
+                       q->flags = (q->flags & ~MACVTAP_FEATURES) | u;
 
                return ret;
 
@@ -1027,8 +1027,9 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
                }
 
                ret = 0;
+               u = q->flags;
                if (copy_to_user(&ifr->ifr_name, vlan->dev->name, IFNAMSIZ) ||
-                   put_user(q->flags, &ifr->ifr_flags))
+                   put_user(u, &ifr->ifr_flags))
                        ret = -EFAULT;
                macvtap_put_vlan(vlan);
                rtnl_unlock();