net/tun: fix ioctl() based info leaks

The tun module leaks up to 36 bytes of memory by not fully initializing
a structure located on the stack that gets copied to user memory by the
TUNGETIFF and SIOCGIFHWADDR ioctl()s.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -1379,9 +1379,11 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	int vnet_hdr_sz;
 	int ret;
 
-	if (cmd == TUNSETIFF || _IOC_TYPE(cmd) == 0x89)
+	if (cmd == TUNSETIFF || _IOC_TYPE(cmd) == 0x89) {
 		if (copy_from_user(&ifr, argp, ifreq_len))
 			return -EFAULT;
+	} else
+		memset(&ifr, 0, sizeof(ifr));
 
 	if (cmd == TUNGETFEATURES) {
 		/* Currently this just means: "what IFF flags are valid?".