socket: fix struct ifreq size in compat ioctl

As reported by Reobert O'Callahan, since Viro's commit to kill
dev_ifsioc() we attempt to copy too much data in compat mode,
which may lead to EFAULT when the 32-bit version of struct ifreq
sits at/near the end of a page boundary, and the next page isn't
mapped.

Fix this by passing the approprate compat/non-compat size to copy
and using that, as before the dev_ifsioc() removal. This works
because only the embedded "struct ifmap" has different size, and
this is only used in SIOCGIFMAP/SIOCSIFMAP which has a different
handler. All other parts of the union are naturally compatible.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=199469.

Fixes: bf4405737f9f ("kill dev_ifsioc()")
Reported-by: Robert O'Callahan <robert@ocallahan.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/socket.c

@@ -941,7 +941,8 @@ void dlci_ioctl_set(int (*hook) (unsigned int, void __user *))
 EXPORT_SYMBOL(dlci_ioctl_set);
 
 static long sock_do_ioctl(struct net *net, struct socket *sock,
-				 unsigned int cmd, unsigned long arg)
+			  unsigned int cmd, unsigned long arg,
+			  unsigned int ifreq_size)
 {
 	int err;
 	void __user *argp = (void __user *)arg;
@@ -967,11 +968,11 @@ static long sock_do_ioctl(struct net *net, struct socket *sock,
 	} else {
 		struct ifreq ifr;
 		bool need_copyout;
-		if (copy_from_user(&ifr, argp, sizeof(struct ifreq)))
+		if (copy_from_user(&ifr, argp, ifreq_size))
 			return -EFAULT;
 		err = dev_ioctl(net, cmd, &ifr, &need_copyout);
 		if (!err && need_copyout)
-			if (copy_to_user(argp, &ifr, sizeof(struct ifreq)))
+			if (copy_to_user(argp, &ifr, ifreq_size))
 				return -EFAULT;
 	}
 	return err;
@@ -1070,7 +1071,8 @@ static long sock_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 			err = open_related_ns(&net->ns, get_net_ns);
 			break;
 		default:
-			err = sock_do_ioctl(net, sock, cmd, arg);
+			err = sock_do_ioctl(net, sock, cmd, arg,
+					    sizeof(struct ifreq));
 			break;
 		}
 	return err;
@@ -2750,7 +2752,8 @@ static int do_siocgstamp(struct net *net, struct socket *sock,
 	int err;
 
 	set_fs(KERNEL_DS);
-	err = sock_do_ioctl(net, sock, cmd, (unsigned long)&ktv);
+	err = sock_do_ioctl(net, sock, cmd, (unsigned long)&ktv,
+			    sizeof(struct compat_ifreq));
 	set_fs(old_fs);
 	if (!err)
 		err = compat_put_timeval(&ktv, up);
@@ -2766,7 +2769,8 @@ static int do_siocgstampns(struct net *net, struct socket *sock,
 	int err;
 
 	set_fs(KERNEL_DS);
-	err = sock_do_ioctl(net, sock, cmd, (unsigned long)&kts);
+	err = sock_do_ioctl(net, sock, cmd, (unsigned long)&kts,
+			    sizeof(struct compat_ifreq));
 	set_fs(old_fs);
 	if (!err)
 		err = compat_put_timespec(&kts, up);
@@ -3072,7 +3076,8 @@ static int routing_ioctl(struct net *net, struct socket *sock,
 	}
 
 	set_fs(KERNEL_DS);
-	ret = sock_do_ioctl(net, sock, cmd, (unsigned long) r);
+	ret = sock_do_ioctl(net, sock, cmd, (unsigned long) r,
+			    sizeof(struct compat_ifreq));
 	set_fs(old_fs);
 
 out:
@@ -3185,7 +3190,8 @@ static int compat_sock_ioctl_trans(struct file *file, struct socket *sock,
 	case SIOCBONDSETHWADDR:
 	case SIOCBONDCHANGEACTIVE:
 	case SIOCGIFNAME:
-		return sock_do_ioctl(net, sock, cmd, arg);
+		return sock_do_ioctl(net, sock, cmd, arg,
+				     sizeof(struct compat_ifreq));
 	}
 
 	return -ENOIOCTLCMD;