udp6: fix potential access to stale information

stable inclusion
from stable-v4.19.281
commit 0638f2b9b220ac33e4657010dd0a130ed0cde7df
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I715PM
CVE: NA

--------------------------------

[ Upstream commit 1c5950fc ]

lena wang reported an issue caused by udpv6_sendmsg()
mangling msg->msg_name and msg->msg_namelen, which
are later read from ____sys_sendmsg() :

	/*
	 * If this is sendmmsg() and sending to current destination address was
	 * successful, remember it.
	 */
	if (used_address && err >= 0) {
		used_address->name_len = msg_sys->msg_namelen;
		if (msg_sys->msg_name)
			memcpy(&used_address->name, msg_sys->msg_name,
			       used_address->name_len);
	}

udpv6_sendmsg() wants to pretend the remote address family
is AF_INET in order to call udp_sendmsg().

A fix would be to modify the address in-place, instead
of using a local variable, but this could have other side effects.

Instead, restore initial values before we return from udpv6_sendmsg().

Fixes: c71d8ebe ("net: Fix security_socket_sendmsg() bypass problem.")
Reported-by: Nlena wang <lena.wang@mediatek.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Reviewed-by: NMaciej Żenczykowski <maze@google.com>
Link: https://lore.kernel.org/r/20230412130308.1202254-1-edumazet@google.comSigned-off-by: NJakub Kicinski <kuba@kernel.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

net/ipv6/udp.c

@@ -1219,9 +1219,11 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 			msg->msg_name = &sin;
 			msg->msg_namelen = sizeof(sin);
 do_udp_sendmsg:
-			if (__ipv6_only_sock(sk))
-				return -ENETUNREACH;
-			return udp_sendmsg(sk, msg, len);
+			err = __ipv6_only_sock(sk) ?
+				-ENETUNREACH : udp_sendmsg(sk, msg, len);
+			msg->msg_name = sin6;
+			msg->msg_namelen = addr_len;
+			return err;
 		}
 	}