libbb/udp_io.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Utility routines.
   4  *
   5  * Copyright (C) 2007 Denys Vlasenko
   6  *
   7  * Licensed under GPLv2, see file LICENSE in this source tree.
   8  */
   9 #include "libbb.h"
  10
  11 #if defined(IPV6_PKTINFO) && !defined(IPV6_RECVPKTINFO)
  12 # define IPV6_RECVPKTINFO IPV6_PKTINFO
  13 #endif
  14
  15 /*
  16  * This asks kernel to let us know dst addr/port of incoming packets
  17  * We don't check for errors here. Not supported == won't be used
  18  */
  19 void FAST_FUNC
  20 socket_want_pktinfo(int fd UNUSED_PARAM)
  21 {
  22 #ifdef IP_PKTINFO
  23         setsockopt_1(fd, IPPROTO_IP, IP_PKTINFO);
  24 #endif
  25 #if ENABLE_FEATURE_IPV6 && defined(IPV6_RECVPKTINFO)
  26         setsockopt_1(fd, IPPROTO_IPV6, IPV6_RECVPKTINFO);
  27 #endif
  28 }
  29
  30
  31 ssize_t FAST_FUNC
  32 send_to_from(int fd, void *buf, size_t len, int flags,
  33                 const struct sockaddr *to,
  34                 const struct sockaddr *from,
  35                 socklen_t tolen)
  36 {
  37 #ifndef IP_PKTINFO
  38         (void)from; /* suppress "unused from" warning */
  39         return sendto(fd, buf, len, flags, to, tolen);
  40 #else
  41         struct iovec iov[1];
  42         struct msghdr msg;
  43         union {
  44                 char cmsg[CMSG_SPACE(sizeof(struct in_pktinfo))];
  45 # if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
  46                 char cmsg6[CMSG_SPACE(sizeof(struct in6_pktinfo))];
  47 # endif
  48         } u;
  49         struct cmsghdr* cmsgptr;
  50
  51         if (from->sa_family != AF_INET
  52 # if ENABLE_FEATURE_IPV6
  53          && from->sa_family != AF_INET6
  54 # endif
  55         ) {
  56                 /* ANY local address */
  57                 return sendto(fd, buf, len, flags, to, tolen);
  58         }
  59
  60         /* man recvmsg and man cmsg is needed to make sense of code below */
  61
  62         iov[0].iov_base = buf;
  63         iov[0].iov_len = len;
  64
  65         memset(&u, 0, sizeof(u));
  66
  67         memset(&msg, 0, sizeof(msg));
  68         msg.msg_name = (void *)(struct sockaddr *)to; /* or compiler will annoy us */
  69         msg.msg_namelen = tolen;
  70         msg.msg_iov = iov;
  71         msg.msg_iovlen = 1;
  72         msg.msg_control = &u;
  73         msg.msg_controllen = sizeof(u);
  74         msg.msg_flags = flags;
  75
  76         cmsgptr = CMSG_FIRSTHDR(&msg);
  77         /*
  78          * Users report that to->sa_family can be AF_INET6 too,
  79          * if "to" was acquired by recv_from_to(). IOW: recv_from_to()
  80          * was seen showing IPv6 "from" even when the destination
  81          * of received packet (our local address) was IPv4.
  82          */
  83         if (/* to->sa_family == AF_INET && */ from->sa_family == AF_INET) {
  84                 struct in_pktinfo *pktptr;
  85                 cmsgptr->cmsg_level = IPPROTO_IP;
  86                 cmsgptr->cmsg_type = IP_PKTINFO;
  87                 cmsgptr->cmsg_len = CMSG_LEN(sizeof(struct in_pktinfo));
  88                 pktptr = (struct in_pktinfo *)(CMSG_DATA(cmsgptr));
  89                 /*pktptr->ipi_ifindex = 0; -- already done by memset(u...) */
  90                 /* In general, CMSG_DATA() can be unaligned, but in this case
  91                  * we know for sure it is sufficiently aligned:
  92                  * CMSG_FIRSTHDR simply returns &u above,
  93                  * and CMSG_DATA returns &u + size_t + int + int.
  94                  * Thus direct assignment is ok:
  95                  */
  96                 pktptr->ipi_spec_dst = ((struct sockaddr_in*)from)->sin_addr;
  97         }
  98 # if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
  99         else if (/* to->sa_family == AF_INET6 && */ from->sa_family == AF_INET6) {
 100                 struct in6_pktinfo *pktptr;
 101                 cmsgptr->cmsg_level = IPPROTO_IPV6;
 102                 cmsgptr->cmsg_type = IPV6_PKTINFO;
 103                 cmsgptr->cmsg_len = CMSG_LEN(sizeof(struct in6_pktinfo));
 104                 pktptr = (struct in6_pktinfo *)(CMSG_DATA(cmsgptr));
 105                 /* pktptr->ipi6_ifindex = 0; -- already done by memset(u...) */
 106                 pktptr->ipi6_addr = ((struct sockaddr_in6*)from)->sin6_addr;
 107         }
 108 # endif
 109         msg.msg_controllen = cmsgptr->cmsg_len;
 110
 111         return sendmsg(fd, &msg, flags);
 112 #endif
 113 }
 114
 115 /* NB: this will never set port# in 'to'!
 116  * _Only_ IP/IPv6 address part of 'to' is _maybe_ modified.
 117  * Typical usage is to preinit 'to' with "default" value
 118  * before calling recv_from_to(). */
 119 ssize_t FAST_FUNC
 120 recv_from_to(int fd, void *buf, size_t len, int flags,
 121                 struct sockaddr *from, struct sockaddr *to,
 122                 socklen_t sa_size)
 123 {
 124 #ifndef IP_PKTINFO
 125         (void)to; /* suppress "unused to" warning */
 126         return recvfrom(fd, buf, len, flags, from, &sa_size);
 127 #else
 128         /* man recvmsg and man cmsg is needed to make sense of code below */
 129         struct iovec iov[1];
 130         union {
 131                 char cmsg[CMSG_SPACE(sizeof(struct in_pktinfo))];
 132 # if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
 133                 char cmsg6[CMSG_SPACE(sizeof(struct in6_pktinfo))];
 134 # endif
 135         } u;
 136         struct cmsghdr *cmsgptr;
 137         struct msghdr msg;
 138         ssize_t recv_length;
 139
 140         iov[0].iov_base = buf;
 141         iov[0].iov_len = len;
 142
 143         memset(&msg, 0, sizeof(msg));
 144         msg.msg_name = (struct sockaddr *)from;
 145         msg.msg_namelen = sa_size;
 146         msg.msg_iov = iov;
 147         msg.msg_iovlen = 1;
 148         msg.msg_control = &u;
 149         msg.msg_controllen = sizeof(u);
 150
 151         recv_length = recvmsg(fd, &msg, flags);
 152         if (recv_length < 0)
 153                 return recv_length;
 154
 155 # define to4 ((struct sockaddr_in*)to)
 156 # define to6 ((struct sockaddr_in6*)to)
 157         /* Here we try to retrieve destination IP and memorize it */
 158         for (cmsgptr = CMSG_FIRSTHDR(&msg);
 159                         cmsgptr != NULL;
 160                         cmsgptr = CMSG_NXTHDR(&msg, cmsgptr)
 161         ) {
 162                 if (cmsgptr->cmsg_level == IPPROTO_IP
 163                  && cmsgptr->cmsg_type == IP_PKTINFO
 164                 ) {
 165                         const int IPI_ADDR_OFF = offsetof(struct in_pktinfo, ipi_addr);
 166                         to->sa_family = AF_INET;
 167                         /*# define pktinfo(cmsgptr) ( (struct in_pktinfo*)(CMSG_DATA(cmsgptr)) )*/
 168                         /*to4->sin_addr = pktinfo(cmsgptr)->ipi_addr; - may be unaligned */
 169                         memcpy(&to4->sin_addr, (char*)(CMSG_DATA(cmsgptr)) + IPI_ADDR_OFF, sizeof(to4->sin_addr));
 170                         /*to4->sin_port = 123; - this data is not supplied by kernel */
 171                         break;
 172                 }
 173 # if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
 174                 if (cmsgptr->cmsg_level == IPPROTO_IPV6
 175                  && cmsgptr->cmsg_type == IPV6_PKTINFO
 176                 ) {
 177                         const int IPI6_ADDR_OFF = offsetof(struct in6_pktinfo, ipi6_addr);
 178                         to->sa_family = AF_INET6;
 179                         /*#  define pktinfo(cmsgptr) ( (struct in6_pktinfo*)(CMSG_DATA(cmsgptr)) )*/
 180                         /*to6->sin6_addr = pktinfo(cmsgptr)->ipi6_addr; - may be unaligned */
 181                         memcpy(&to6->sin6_addr, (char*)(CMSG_DATA(cmsgptr)) + IPI6_ADDR_OFF, sizeof(to6->sin6_addr));
 182                         /*to6->sin6_port = 123; */
 183                         break;
 184                 }
 185 # endif
 186         }
 187         return recv_length;
 188 #endif
 189 }