pppd: Define request and response rtnetlink IPv6 structures

This simplify understanding of rtnetlink IPv6 API. Also it simplify
code for filling rtnetlink IPv6 address request message and reading
rtnetlink response message as it avoids usage of pointer arithmetic.

Signed-off-by: Pali Rohár <pali@kernel.org>

diff --git a/pppd/sys-linux.c b/pppd/sys-linux.c
index 3ec7860ff4cd1c5101198f77766b00544b6e9592..b0ad508185336785a80a156a81e9948bb5cd3cc4 100644 (file)
--- a/pppd/sys-linux.c
+++ b/pppd/sys-linux.c
@@ -2838,16 +2838,22 @@ int cifaddr (int unit, u_int32_t our_adr, u_int32_t his_adr)
  */
 static int sif6addr_rtnetlink(unsigned int iface, eui64_t our_eui64, eui64_t his_eui64)
 {
-    struct msghdr msg;
-    struct sockaddr_nl sa;
+    struct {
+        struct nlmsghdr nlh;
+        struct ifaddrmsg ifa;
+        struct {
+            struct rtattr rta;
+            struct in6_addr addr;
+        } addrs[2];
+    } nlreq;
+    struct {
+        struct nlmsghdr nlh;
+        struct nlmsgerr nlerr;
+    } nlresp;
+    struct sockaddr_nl nladdr;
     struct iovec iov;
-    struct nlmsghdr *nlmsg;
-    struct ifaddrmsg *ifa;
-    struct rtattr *local_rta;
-    struct rtattr *remote_rta;
-    char buf[NLMSG_LENGTH(sizeof(*ifa) + 2*RTA_LENGTH(sizeof(struct in6_addr)))];
-    ssize_t nlmsg_len;
-    struct nlmsgerr *errmsg;
+    struct msghdr msg;
+    ssize_t nlresplen;
     int one;
     int fd;
 
@@ -2869,60 +2875,43 @@ static int sif6addr_rtnetlink(unsigned int iface, eui64_t our_eui64, eui64_t his
     one = 1;
     setsockopt(fd, SOL_NETLINK, NETLINK_CAP_ACK, &one, sizeof(one));
 
-    memset(&sa, 0, sizeof(sa));
-    sa.nl_family = AF_NETLINK;
-    sa.nl_pid = 0;
-    sa.nl_groups = 0;
+    memset(&nladdr, 0, sizeof(nladdr));
+    nladdr.nl_family = AF_NETLINK;
 
-    if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
+    if (bind(fd, (struct sockaddr *)&nladdr, sizeof(nladdr)) < 0) {
         error("sif6addr_rtnetlink: bind(AF_NETLINK): %m (line %d)", __LINE__);
         close(fd);
         return 0;
     }
 
-    memset(buf, 0, sizeof(buf));
-
-    nlmsg = (struct nlmsghdr *)buf;
-    nlmsg->nlmsg_len = sizeof(buf);
-    nlmsg->nlmsg_type = RTM_NEWADDR;
-    nlmsg->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_EXCL | NLM_F_CREATE;
-    nlmsg->nlmsg_seq = 1;
-    nlmsg->nlmsg_pid = 0;
-
-    ifa = NLMSG_DATA(nlmsg);
-    ifa->ifa_family = AF_INET6;
-    ifa->ifa_prefixlen = 128;
-    ifa->ifa_flags = IFA_F_NODAD | IFA_F_PERMANENT;
-    ifa->ifa_scope = RT_SCOPE_LINK;
-    ifa->ifa_index = iface;
-
-    local_rta = IFA_RTA(ifa);
-    local_rta->rta_len = RTA_LENGTH(sizeof(struct in6_addr));
-    local_rta->rta_type = IFA_LOCAL;
-    IN6_LLADDR_FROM_EUI64(*(struct in6_addr *)RTA_DATA(local_rta), our_eui64);
-
-    remote_rta = (struct rtattr *)((char *)local_rta + local_rta->rta_len);
-    remote_rta->rta_len = RTA_LENGTH(sizeof(struct in6_addr));
-    remote_rta->rta_type = IFA_ADDRESS;
-    IN6_LLADDR_FROM_EUI64(*(struct in6_addr *)RTA_DATA(remote_rta), his_eui64);
-
-    memset(&sa, 0, sizeof(sa));
-    sa.nl_family = AF_NETLINK;
-    sa.nl_pid = 0;
-    sa.nl_groups = 0;
+    memset(&nlreq, 0, sizeof(nlreq));
+    nlreq.nlh.nlmsg_len = sizeof(nlreq);
+    nlreq.nlh.nlmsg_type = RTM_NEWADDR;
+    nlreq.nlh.nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | NLM_F_EXCL | NLM_F_CREATE;
+    nlreq.ifa.ifa_family = AF_INET6;
+    nlreq.ifa.ifa_prefixlen = 128;
+    nlreq.ifa.ifa_flags = IFA_F_NODAD | IFA_F_PERMANENT;
+    nlreq.ifa.ifa_scope = RT_SCOPE_LINK;
+    nlreq.ifa.ifa_index = iface;
+    nlreq.addrs[0].rta.rta_len = sizeof(nlreq.addrs[0]);
+    nlreq.addrs[0].rta.rta_type = IFA_LOCAL;
+    IN6_LLADDR_FROM_EUI64(nlreq.addrs[0].addr, our_eui64);
+    nlreq.addrs[1].rta.rta_len = sizeof(nlreq.addrs[1]);
+    nlreq.addrs[1].rta.rta_type = IFA_ADDRESS;
+    IN6_LLADDR_FROM_EUI64(nlreq.addrs[1].addr, his_eui64);
+
+    memset(&nladdr, 0, sizeof(nladdr));
+    nladdr.nl_family = AF_NETLINK;
 
     memset(&iov, 0, sizeof(iov));
-    iov.iov_base = nlmsg;
-    iov.iov_len = nlmsg->nlmsg_len;
+    iov.iov_base = &nlreq;
+    iov.iov_len = sizeof(nlreq);
 
     memset(&msg, 0, sizeof(msg));
-    msg.msg_name = &sa;
-    msg.msg_namelen = sizeof(sa);
+    msg.msg_name = &nladdr;
+    msg.msg_namelen = sizeof(nladdr);
     msg.msg_iov = &iov;
     msg.msg_iovlen = 1;
-    msg.msg_control = NULL;
-    msg.msg_controllen = 0;
-    msg.msg_flags = 0;
 
     if (sendmsg(fd, &msg, 0) < 0) {
         error("sif6addr_rtnetlink: sendmsg(RTM_NEWADDR/NLM_F_CREATE): %m (line %d)", __LINE__);
@@ -2931,21 +2920,18 @@ static int sif6addr_rtnetlink(unsigned int iface, eui64_t our_eui64, eui64_t his
     }
 
     memset(&iov, 0, sizeof(iov));
-    iov.iov_base = buf;
-    iov.iov_len = sizeof(buf);
+    iov.iov_base = &nlresp;
+    iov.iov_len = sizeof(nlresp);
 
     memset(&msg, 0, sizeof(msg));
-    msg.msg_name = NULL;
-    msg.msg_namelen = 0;
+    msg.msg_name = &nladdr;
+    msg.msg_namelen = sizeof(nladdr);
     msg.msg_iov = &iov;
     msg.msg_iovlen = 1;
-    msg.msg_control = NULL;
-    msg.msg_controllen = 0;
-    msg.msg_flags = 0;
 
-    nlmsg_len = recvmsg(fd, &msg, 0);
+    nlresplen = recvmsg(fd, &msg, 0);
 
-    if (nlmsg_len < 0) {
+    if (nlresplen < 0) {
         error("sif6addr_rtnetlink: recvmsg(NLM_F_ACK): %m (line %d)", __LINE__);
         close(fd);
         return 0;
@@ -2953,29 +2939,25 @@ static int sif6addr_rtnetlink(unsigned int iface, eui64_t our_eui64, eui64_t his
 
     close(fd);
 
-    if ((size_t)nlmsg_len < sizeof(*nlmsg)) {
-        error("sif6addr_rtnetlink: recvmsg(NLM_F_ACK): Packet too short (line %d)", __LINE__);
+    if (nladdr.nl_family != AF_NETLINK) {
+        error("sif6addr_rtnetlink: recvmsg(NLM_F_ACK): Not a netlink packet (line %d)", __LINE__);
         return 0;
     }
 
-    nlmsg = (struct nlmsghdr *)buf;
-
-    /* acknowledgment packet for NLM_F_ACK is NLMSG_ERROR */
-    if (nlmsg->nlmsg_type != NLMSG_ERROR) {
-        error("sif6addr_rtnetlink: recvmsg(NLM_F_ACK): Not an acknowledgment packet (line %d)", __LINE__);
+    if ((size_t)nlresplen != sizeof(nlresp) || nlresp.nlh.nlmsg_len < sizeof(nlresp)) {
+        error("sif6addr_rtnetlink: recvmsg(NLM_F_ACK): Acknowledgment netlink packet too short (line %d)", __LINE__);
         return 0;
     }
 
-    if ((size_t)nlmsg_len < NLMSG_LENGTH(sizeof(*errmsg))) {
-        error("sif6addr_rtnetlink: recvmsg(NLM_F_ACK): Packet too short (line %d)", __LINE__);
+    /* acknowledgment packet for NLM_F_ACK is NLMSG_ERROR */
+    if (nlresp.nlh.nlmsg_type != NLMSG_ERROR) {
+        error("sif6addr_rtnetlink: recvmsg(NLM_F_ACK): Not an acknowledgment netlink packet (line %d)", __LINE__);
         return 0;
     }
 
-    errmsg = NLMSG_DATA(nlmsg);
-
     /* error == 0 indicates success, negative value is errno code */
-    if (errmsg->error != 0) {
-        error("sif6addr_rtnetlink: %s (line %d)", strerror(-errmsg->error), __LINE__);
+    if (nlresp.nlerr.error != 0) {
+        error("sif6addr_rtnetlink: %s (line %d)", strerror(-nlresp.nlerr.error), __LINE__);
         return 0;
     }