af_key: fix buffer overread in verify_address_len()

If a message sent to a PF_KEY socket ended with one of the extensions
that takes a 'struct sadb_address' but there were not enough bytes
remaining in the message for the ->sa_family member of the 'struct
sockaddr' which is supposed to follow, then verify_address_len() read
past the end of the message, into uninitialized memory.  Fix it by
returning -EINVAL in this case.

This bug was found using syzkaller with KMSAN.

Reproducer:

	#include <linux/pfkeyv2.h>
	#include <sys/socket.h>
	#include <unistd.h>

	int main()
	{
		int sock = socket(PF_KEY, SOCK_RAW, PF_KEY_V2);
		char buf[24] = { 0 };
		struct sadb_msg *msg = (void *)buf;
		struct sadb_address *addr = (void *)(msg + 1);

		msg->sadb_msg_version = PF_KEY_V2;
		msg->sadb_msg_type = SADB_DELETE;
		msg->sadb_msg_len = 3;
		addr->sadb_address_len = 1;
		addr->sadb_address_exttype = SADB_EXT_ADDRESS_SRC;

		write(sock, buf, 24);
	}
Reported-by: Alexander Potapenko <glider@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/key/af_key.c

@@ -401,6 +401,11 @@ static int verify_address_len(const void *p)
 #endif
 	int len;
 
+	if (sp->sadb_address_len <
+	    DIV_ROUND_UP(sizeof(*sp) + offsetofend(typeof(*addr), sa_family),
+			 sizeof(uint64_t)))
+		return -EINVAL;
+
 	switch (addr->sa_family) {
 	case AF_INET:
 		len = DIV_ROUND_UP(sizeof(*sp) + sizeof(*sin), sizeof(uint64_t));