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

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Date:   Wed, 14 Sep 2022 18:48:52 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     syzbot <syzbot+a448cda4dba2dac50de5@...kaller.appspotmail.com>,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux-next@...r.kernel.org,
        netdev@...r.kernel.org, pabeni@...hat.com, sfr@...b.auug.org.au,
        syzkaller-bugs@...glegroups.com, wireguard@...ts.zx2c4.com
Subject: Re: [syzbot] linux-next test error: WARNING in set_peer

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@...c4.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@...omium.org>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.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