From 4abab5ad6c8465a7528ccdd5f49367da05f78bbd Mon Sep 17 00:00:00 2001
From: Vladimir Azarov <avm@intermediate-node.net>
Date: Tue, 1 Oct 2024 15:47:05 +0200
Subject: Initial version

---
 src/network/res_msend.c | 325 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 325 insertions(+)
 create mode 100644 src/network/res_msend.c

(limited to 'src/network/res_msend.c')

diff --git a/src/network/res_msend.c b/src/network/res_msend.c
new file mode 100644
index 0000000..86c2fcf
--- /dev/null
+++ b/src/network/res_msend.c
@@ -0,0 +1,325 @@
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <netdb.h>
+#include <arpa/inet.h>
+#include <stdint.h>
+#include <string.h>
+#include <poll.h>
+#include <time.h>
+#include <ctype.h>
+#include <unistd.h>
+#include <errno.h>
+#include <pthread.h>
+#include "stdio_impl.h"
+#include "syscall.h"
+#include "lookup.h"
+
+static void cleanup(void *p)
+{
+	struct pollfd *pfd = p;
+	for (int i=0; pfd[i].fd >= -1; i++)
+		if (pfd[i].fd >= 0) __syscall(SYS_close, pfd[i].fd);
+}
+
+static unsigned long mtime()
+{
+	struct timespec ts;
+	if (clock_gettime(CLOCK_MONOTONIC, &ts) < 0 && errno == ENOSYS)
+		clock_gettime(CLOCK_REALTIME, &ts);
+	return (unsigned long)ts.tv_sec * 1000
+		+ ts.tv_nsec / 1000000;
+}
+
+static int start_tcp(struct pollfd *pfd, int family, const void *sa, socklen_t sl, const unsigned char *q, int ql)
+{
+	struct msghdr mh = {
+		.msg_name = (void *)sa,
+		.msg_namelen = sl,
+		.msg_iovlen = 2,
+		.msg_iov = (struct iovec [2]){
+			{ .iov_base = (uint8_t[]){ ql>>8, ql }, .iov_len = 2 },
+			{ .iov_base = (void *)q, .iov_len = ql } }
+	};
+	int r;
+	int fd = socket(family, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+	pfd->fd = fd;
+	pfd->events = POLLOUT;
+	if (!setsockopt(fd, IPPROTO_TCP, TCP_FASTOPEN_CONNECT,
+	    &(int){1}, sizeof(int))) {
+		r = sendmsg(fd, &mh, MSG_FASTOPEN|MSG_NOSIGNAL);
+		if (r == ql+2) pfd->events = POLLIN;
+		if (r >= 0) return r;
+		if (errno == EINPROGRESS) return 0;
+	}
+	r = connect(fd, sa, sl);
+	if (!r || errno == EINPROGRESS) return 0;
+	close(fd);
+	pfd->fd = -1;
+	return -1;
+}
+
+static void step_mh(struct msghdr *mh, size_t n)
+{
+	/* Adjust iovec in msghdr to skip first n bytes. */
+	while (mh->msg_iovlen && n >= mh->msg_iov->iov_len) {
+		n -= mh->msg_iov->iov_len;
+		mh->msg_iov++;
+		mh->msg_iovlen--;
+	}
+	if (!mh->msg_iovlen) return;
+	mh->msg_iov->iov_base = (char *)mh->msg_iov->iov_base + n;
+	mh->msg_iov->iov_len -= n;
+}
+
+/* Internal contract for __res_msend[_rc]: asize must be >=512, nqueries
+ * must be sufficiently small to be safe as VLA size. In practice it's
+ * either 1 or 2, anyway. */
+
+int __res_msend_rc(int nqueries, const unsigned char *const *queries,
+	const int *qlens, unsigned char *const *answers, int *alens, int asize,
+	const struct resolvconf *conf)
+{
+	int fd;
+	int timeout, attempts, retry_interval, servfail_retry;
+	union {
+		struct sockaddr_in sin;
+		struct sockaddr_in6 sin6;
+	} sa = {0}, ns[MAXNS] = {{0}};
+	socklen_t sl = sizeof sa.sin;
+	int nns = 0;
+	int family = AF_INET;
+	int rlen;
+	int next;
+	int i, j;
+	int cs;
+	struct pollfd pfd[nqueries+2];
+	int qpos[nqueries], apos[nqueries];
+	unsigned char alen_buf[nqueries][2];
+	int r;
+	unsigned long t0, t1, t2;
+
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
+
+	timeout = 1000*conf->timeout;
+	attempts = conf->attempts;
+
+	for (nns=0; nns<conf->nns; nns++) {
+		const struct address *iplit = &conf->ns[nns];
+		if (iplit->family == AF_INET) {
+			memcpy(&ns[nns].sin.sin_addr, iplit->addr, 4);
+			ns[nns].sin.sin_port = htons(53);
+			ns[nns].sin.sin_family = AF_INET;
+		} else {
+			sl = sizeof sa.sin6;
+			memcpy(&ns[nns].sin6.sin6_addr, iplit->addr, 16);
+			ns[nns].sin6.sin6_port = htons(53);
+			ns[nns].sin6.sin6_scope_id = iplit->scopeid;
+			ns[nns].sin6.sin6_family = family = AF_INET6;
+		}
+	}
+
+	/* Get local address and open/bind a socket */
+	fd = socket(family, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+
+	/* Handle case where system lacks IPv6 support */
+	if (fd < 0 && family == AF_INET6 && errno == EAFNOSUPPORT) {
+		for (i=0; i<nns && conf->ns[nns].family == AF_INET6; i++);
+		if (i==nns) {
+			pthread_setcancelstate(cs, 0);
+			return -1;
+		}
+		fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+		family = AF_INET;
+		sl = sizeof sa.sin;
+	}
+
+	/* Convert any IPv4 addresses in a mixed environment to v4-mapped */
+	if (fd >= 0 && family == AF_INET6) {
+		setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &(int){0}, sizeof 0);
+		for (i=0; i<nns; i++) {
+			if (ns[i].sin.sin_family != AF_INET) continue;
+			memcpy(ns[i].sin6.sin6_addr.s6_addr+12,
+				&ns[i].sin.sin_addr, 4);
+			memcpy(ns[i].sin6.sin6_addr.s6_addr,
+				"\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
+			ns[i].sin6.sin6_family = AF_INET6;
+			ns[i].sin6.sin6_flowinfo = 0;
+			ns[i].sin6.sin6_scope_id = 0;
+		}
+	}
+
+	sa.sin.sin_family = family;
+	if (fd < 0 || bind(fd, (void *)&sa, sl) < 0) {
+		if (fd >= 0) close(fd);
+		pthread_setcancelstate(cs, 0);
+		return -1;
+	}
+
+	/* Past this point, there are no errors. Each individual query will
+	 * yield either no reply (indicated by zero length) or an answer
+	 * packet which is up to the caller to interpret. */
+
+	for (i=0; i<nqueries; i++) pfd[i].fd = -1;
+	pfd[nqueries].fd = fd;
+	pfd[nqueries].events = POLLIN;
+	pfd[nqueries+1].fd = -2;
+
+	pthread_cleanup_push(cleanup, pfd);
+	pthread_setcancelstate(cs, 0);
+
+	memset(alens, 0, sizeof *alens * nqueries);
+
+	retry_interval = timeout / attempts;
+	next = 0;
+	t0 = t2 = mtime();
+	t1 = t2 - retry_interval;
+
+	for (; t2-t0 < timeout; t2=mtime()) {
+		/* This is the loop exit condition: that all queries
+		 * have an accepted answer. */
+		for (i=0; i<nqueries && alens[i]>0; i++);
+		if (i==nqueries) break;
+
+		if (t2-t1 >= retry_interval) {
+			/* Query all configured namservers in parallel */
+			for (i=0; i<nqueries; i++)
+				if (!alens[i])
+					for (j=0; j<nns; j++)
+						sendto(fd, queries[i],
+							qlens[i], MSG_NOSIGNAL,
+							(void *)&ns[j], sl);
+			t1 = t2;
+			servfail_retry = 2 * nqueries;
+		}
+
+		/* Wait for a response, or until time to retry */
+		if (poll(pfd, nqueries+1, t1+retry_interval-t2) <= 0) continue;
+
+		while (next < nqueries) {
+			struct msghdr mh = {
+				.msg_name = (void *)&sa,
+				.msg_namelen = sl,
+				.msg_iovlen = 1,
+				.msg_iov = (struct iovec []){
+					{ .iov_base = (void *)answers[next],
+					  .iov_len = asize }
+				}
+			};
+			rlen = recvmsg(fd, &mh, 0);
+			if (rlen < 0) break;
+
+			/* Ignore non-identifiable packets */
+			if (rlen < 4) continue;
+
+			/* Ignore replies from addresses we didn't send to */
+			for (j=0; j<nns && memcmp(ns+j, &sa, sl); j++);
+			if (j==nns) continue;
+
+			/* Find which query this answer goes with, if any */
+			for (i=next; i<nqueries && (
+				answers[next][0] != queries[i][0] ||
+				answers[next][1] != queries[i][1] ); i++);
+			if (i==nqueries) continue;
+			if (alens[i]) continue;
+
+			/* Only accept positive or negative responses;
+			 * retry immediately on server failure, and ignore
+			 * all other codes such as refusal. */
+			switch (answers[next][3] & 15) {
+			case 0:
+			case 3:
+				break;
+			case 2:
+				if (servfail_retry && servfail_retry--)
+					sendto(fd, queries[i],
+						qlens[i], MSG_NOSIGNAL,
+						(void *)&ns[j], sl);
+			default:
+				continue;
+			}
+
+			/* Store answer in the right slot, or update next
+			 * available temp slot if it's already in place. */
+			alens[i] = rlen;
+			if (i == next)
+				for (; next<nqueries && alens[next]; next++);
+			else
+				memcpy(answers[i], answers[next], rlen);
+
+			/* Ignore further UDP if all slots full or TCP-mode */
+			if (next == nqueries) pfd[nqueries].events = 0;
+
+			/* If answer is truncated (TC bit), fallback to TCP */
+			if ((answers[i][2] & 2) || (mh.msg_flags & MSG_TRUNC)) {
+				alens[i] = -1;
+				pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, 0);
+				r = start_tcp(pfd+i, family, ns+j, sl, queries[i], qlens[i]);
+				pthread_setcancelstate(cs, 0);
+				if (r >= 0) {
+					qpos[i] = r;
+					apos[i] = 0;
+				}
+				continue;
+			}
+		}
+
+		for (i=0; i<nqueries; i++) if (pfd[i].revents & POLLOUT) {
+			struct msghdr mh = {
+				.msg_iovlen = 2,
+				.msg_iov = (struct iovec [2]){
+					{ .iov_base = (uint8_t[]){ qlens[i]>>8, qlens[i] }, .iov_len = 2 },
+					{ .iov_base = (void *)queries[i], .iov_len = qlens[i] } }
+			};
+			step_mh(&mh, qpos[i]);
+			r = sendmsg(pfd[i].fd, &mh, MSG_NOSIGNAL);
+			if (r < 0) goto out;
+			qpos[i] += r;
+			if (qpos[i] == qlens[i]+2)
+				pfd[i].events = POLLIN;
+		}
+
+		for (i=0; i<nqueries; i++) if (pfd[i].revents & POLLIN) {
+			struct msghdr mh = {
+				.msg_iovlen = 2,
+				.msg_iov = (struct iovec [2]){
+					{ .iov_base = alen_buf[i], .iov_len = 2 },
+					{ .iov_base = answers[i], .iov_len = asize } }
+			};
+			step_mh(&mh, apos[i]);
+			r = recvmsg(pfd[i].fd, &mh, 0);
+			if (r <= 0) goto out;
+			apos[i] += r;
+			if (apos[i] < 2) continue;
+			int alen = alen_buf[i][0]*256 + alen_buf[i][1];
+			if (alen < 13) goto out;
+			if (apos[i] < alen+2 && apos[i] < asize+2)
+				continue;
+			int rcode = answers[i][3] & 15;
+			if (rcode != 0 && rcode != 3)
+				goto out;
+
+			/* Storing the length here commits the accepted answer.
+			 * Immediately close TCP socket so as not to consume
+			 * resources we no longer need. */
+			alens[i] = alen;
+			__syscall(SYS_close, pfd[i].fd);
+			pfd[i].fd = -1;
+		}
+	}
+out:
+	pthread_cleanup_pop(1);
+
+	/* Disregard any incomplete TCP results */
+	for (i=0; i<nqueries; i++) if (alens[i]<0) alens[i] = 0;
+
+	return 0;
+}
+
+int __res_msend(int nqueries, const unsigned char *const *queries,
+	const int *qlens, unsigned char *const *answers, int *alens, int asize)
+{
+	struct resolvconf conf;
+	if (__get_resolv_conf(&conf, 0, 0) < 0) return -1;
+	return __res_msend_rc(nqueries, queries, qlens, answers, alens, asize, &conf);
+}
-- 
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