Re: [syzbot] linux-next test error: WARNING in set_peer

Jason A. Donenfeld
2022-09-14T17:49:05Z

I think I'll open code it like below. I'll include this in my next push
to net.

From 19fb26af00a8266df65b706dc02727c6a608b1b6 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Wed, 14 Sep 2022 18:42:00 +0100
Subject: [PATCH] wireguard: netlink: avoid variable-sized memcpy on sockaddr

Doing a variable-sized memcpy is slower, and the compiler isn't smart
enough to turn this into a constant-size assignment.

Further, Kees' latest fortified memcpy will actually bark, because the
destination pointer is type sockaddr, not explicitly sockaddr_in or
sockaddr_in6, so it thinks there's an overflow:

memcpy: detected field-spanning write (size 28) of single field
"&endpoint.addr" at drivers/net/wireguard/netlink.c:446 (size 16)

Fix this by just assigning by using explicit casts for each checked
case.

Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
drivers/net/wireguard/netlink.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wireguard/netlink.c b/drivers/net/wireguard/netlink.c
index d0f3b6d7f408..5c804bcabfe6 100644
--- a/drivers/net/wireguard/netlink.c
+++ b/drivers/net/wireguard/netlink.c
@@ -436,14 +436,13 @@ static int set_peer(struct wg_device *wg, struct nlattr **attrs)
if (attrs[WGPEER_A_ENDPOINT]) {
struct sockaddr *addr = nla_data(attrs[WGPEER_A_ENDPOINT]);
size_t len = nla_len(attrs[WGPEER_A_ENDPOINT]);
+ struct endpoint endpoint = { { { 0 } } };

- if ((len == sizeof(struct sockaddr_in) &&
- addr->sa_family == AF_INET) ||
- (len == sizeof(struct sockaddr_in6) &&
- addr->sa_family == AF_INET6)) {
- struct endpoint endpoint = { { { 0 } } };
-
- memcpy(&endpoint.addr, addr, len);
+ if (len == sizeof(struct sockaddr_in) && addr->sa_family == AF_INET) {
+ endpoint.addr4 = *(struct sockaddr_in *)addr;
+ wg_socket_set_peer_endpoint(peer, &endpoint);
+ } else if (len == sizeof(struct sockaddr_in6) && addr->sa_family == AF_INET6) {
+ endpoint.addr6 = *(struct sockaddr_in6 *)addr;
wg_socket_set_peer_endpoint(peer, &endpoint);
}
}
--
2.37.3