netlink: Make nl_*_dup() use a separate datagram for each request

nl_req() is designed to handle a single netlink request message: it only
receives a single reply datagram for the request, and only waits for a
single NLMSG_DONE or NLMSG_ERROR message at the beginning to clear out
things from previous requests.

However, in both nl_addr_dup() and nl_route_dup() we can send multiple
request messages as a single datagram, with a single nl_req() call.
This can easily mean that the replies nl_req() collects get out of
sync with requests.  We only get away with this because after we call
these functions we don't make any netlink calls where we need to parse
the replies.

This is fragile, so alter nl_*_dup() to make an nl_req() call for each
address it is adding in the target namespace.

For nl_route_dup() this fixes an additional minor problem: because
routes can have dependencies, some of the route add requests might
fail on the first attempt, so we need to repeat the requests a number
of times.  When we did that, we weren't updating the sequence number
on each new attempt.  This works, but not updating the sequence number
for each new request isn't ideal.  Now that we're making the requests
one at a time, it's easier to make sure we update the sequence number
each time.

Link: https://bugs.passt.top/show_bug.cgi?id=67
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

netlink.c

@@ -351,18 +351,16 @@ void nl_route_dup(int s_src, unsigned int ifi_src,
 		.rta.rta_len	  = RTA_LENGTH(sizeof(unsigned int)),
 		.ifi		  = ifi_src,
 	};
-	char buf[NLBUFSIZ], resp[NLBUFSIZ];
 	unsigned dup_routes = 0;
 	ssize_t n, nlmsgs_size;
 	struct nlmsghdr *nh;
+	char buf[NLBUFSIZ];
 	unsigned i;
 
-	if ((n = nl_req(s_src, buf, &req, req.nlh.nlmsg_len)) < 0)
+	if ((nlmsgs_size = nl_req(s_src, buf, &req, req.nlh.nlmsg_len)) < 0)
 		return;
 
-	nlmsgs_size = n;
+	for (nh = (struct nlmsghdr *)buf, n = nlmsgs_size;
-
-	for (nh = (struct nlmsghdr *)buf;
 	     NLMSG_OK(nh, n) && nh->nlmsg_type != NLMSG_DONE;
 	     nh = NLMSG_NEXT(nh, n)) {
 		struct rtmsg *rtm = (struct rtmsg *)NLMSG_DATA(nh);
@@ -372,7 +370,6 @@ void nl_route_dup(int s_src, unsigned int ifi_src,
 		if (nh->nlmsg_type != RTM_NEWROUTE)
 			continue;
 
-		nh->nlmsg_seq = nl_seq++;
 		nh->nlmsg_pid = 0;
 		nh->nlmsg_flags &= ~NLM_F_DUMP_FILTERED;
 		nh->nlmsg_flags |= NLM_F_REQUEST | NLM_F_ACK |
@@ -386,16 +383,26 @@ void nl_route_dup(int s_src, unsigned int ifi_src,
 		}
 	}
 
-	nh = (struct nlmsghdr *)buf;
 	/* Routes might have dependencies between each other, and the kernel
-	 * processes RTM_NEWROUTE messages sequentially. For n valid routes, we
+	 * processes RTM_NEWROUTE messages sequentially. For n routes, we might
-	 * might need to send up to n requests to get all of them inserted.
+	 * need to send the requests up to n times to get all of them inserted.
-	 * Routes that have been already inserted won't cause the whole request
+	 * Routes that have been already inserted will return -EEXIST, but we
-	 * to fail, so we can simply repeat the whole request. This approach
+	 * can safely ignore that and repeat the requests. This avoids the need
-	 * avoids the need to calculate dependencies: let the kernel do that.
+	 * to calculate dependencies: let the kernel do that.
 	 */
-	for (i = 0; i < dup_routes; i++)
+	for (i = 0; i < dup_routes; i++) {
-		nl_req(s_dst, resp, nh, nlmsgs_size);
+		for (nh = (struct nlmsghdr *)buf, n = nlmsgs_size;
+		     NLMSG_OK(nh, n) && nh->nlmsg_type != NLMSG_DONE;
+		     nh = NLMSG_NEXT(nh, n)) {
+			char resp[NLBUFSIZ];
+
+			if (nh->nlmsg_type != RTM_NEWROUTE)
+				continue;
+
+			nh->nlmsg_seq = nl_seq++;
+			nl_req(s_dst, resp, nh, nh->nlmsg_len);
+		}
+	}
 }
 
 /**
@@ -559,19 +566,18 @@ void nl_addr_dup(int s_src, unsigned int ifi_src,
 		.ifa.ifa_index     = ifi_src,
 		.ifa.ifa_prefixlen = 0,
 	};
-	char buf[NLBUFSIZ], resp[NLBUFSIZ];
+	char buf[NLBUFSIZ];
-	ssize_t n, nlmsgs_size;
 	struct nlmsghdr *nh;
+	ssize_t n;
 
 	if ((n = nl_req(s_src, buf, &req, sizeof(req))) < 0)
 		return;
 
-	nlmsgs_size = n;
-
 	for (nh = (struct nlmsghdr *)buf;
 	     NLMSG_OK(nh, n) && nh->nlmsg_type != NLMSG_DONE;
 	     nh = NLMSG_NEXT(nh, n)) {
 		struct ifaddrmsg *ifa;
+		char resp[NLBUFSIZ];
 		struct rtattr *rta;
 		size_t na;
 
@@ -586,10 +592,8 @@ void nl_addr_dup(int s_src, unsigned int ifi_src,
 		ifa = (struct ifaddrmsg *)NLMSG_DATA(nh);
 
 		if (ifa->ifa_scope == RT_SCOPE_LINK ||
-		    ifa->ifa_index != ifi_src) {
+		    ifa->ifa_index != ifi_src)
-			ifa->ifa_family = AF_UNSPEC;
 			continue;
-		}
 
 		ifa->ifa_index = ifi_dst;
 
@@ -598,9 +602,9 @@ void nl_addr_dup(int s_src, unsigned int ifi_src,
 			if (rta->rta_type == IFA_LABEL)
 				rta->rta_type = IFA_UNSPEC;
 		}
-	}
 
-	nl_req(s_dst, resp, buf, nlmsgs_size);
+		nl_req(s_dst, resp, nh, nh->nlmsg_len);
+	}
 }
 
 /**