mdw@git.distorted.org.uk Git - secnet/blob - udp.c

   1 /* UDP send/receive module for secnet */
   2
   3 /* This module enables sites to communicate by sending UDP
   4  * packets. When an instance of the module is created we can
   5  * optionally bind to a particular local IP address (not implemented
   6  * yet).
   7  *
   8  * Packets are offered to registered receivers in turn. Once one
   9  * accepts it, it isn't offered to any more. */
  10
  11 #include "secnet.h"
  12 #include <stdio.h>
  13 #include <unistd.h>
  14 #include <fcntl.h>
  15 #include <string.h>
  16 #include <errno.h>
  17 #include <sys/socket.h>
  18 #include <sys/wait.h>
  19 #include <netinet/in.h>
  20 #include <arpa/inet.h>
  21 #include "util.h"
  22 #include "magic.h"
  23 #include "unaligned.h"
  24 #include "ipaddr.h"
  25 #include "magic.h"
  26
  27 static beforepoll_fn udp_beforepoll;
  28 static afterpoll_fn udp_afterpoll;
  29 static comm_request_notify_fn request_notify;
  30 static comm_release_notify_fn release_notify;
  31 static comm_sendmsg_fn udp_sendmsg;
  32
  33 struct notify_list {
  34     comm_notify_fn *fn;
  35     void *state;
  36     struct notify_list *next;
  37 };
  38
  39 struct udp {
  40     closure_t cl;
  41     struct comm_if ops;
  42     struct cloc loc;
  43     uint32_t addr;
  44     uint16_t port;
  45     int fd;
  46     string_t authbind;
  47     struct buffer_if *rbuf;
  48     struct notify_list *notify;
  49     bool_t use_proxy;
  50     struct sockaddr_in proxy;
  51 };
  52
  53 static const char *saddr_to_string(const struct sockaddr_in *sin) {
  54     static char bufs[2][100];
  55     static int b;
  56
  57     b ^= 1;
  58     snprintf(bufs[b], sizeof(bufs[b]), "[%s]:%d",
  59              inet_ntoa(sin->sin_addr),
  60              ntohs(sin->sin_port));
  61     return bufs[b];
  62 }
  63
  64 static const char *addr_to_string(void *commst, const struct comm_addr *ca) {
  65     struct udp *st=commst;
  66     static char sbuf[100];
  67
  68     struct sockaddr_in la;
  69     la.sin_addr.s_addr=htonl(st->addr);
  70     la.sin_port=htons(st->port);
  71
  72     snprintf(sbuf, sizeof(sbuf), "udp:%s-%s",
  73              saddr_to_string(&la), saddr_to_string(&ca->sin));
  74     return sbuf;
  75 }
  76
  77 static int udp_beforepoll(void *state, struct pollfd *fds, int *nfds_io,
  78                           int *timeout_io)
  79 {
  80     struct udp *st=state;
  81     if (*nfds_io<1) {
  82         *nfds_io=1;
  83         return ERANGE;
  84     }
  85     *nfds_io=1;
  86     fds->fd=st->fd;
  87     fds->events=POLLIN;
  88     return 0;
  89 }
  90
  91 static void udp_afterpoll(void *state, struct pollfd *fds, int nfds)
  92 {
  93     struct udp *st=state;
  94     struct sockaddr_in from;
  95     socklen_t fromlen;
  96     struct notify_list *n;
  97     bool_t done;
  98     int rv;
  99
 100     if (nfds && (fds->revents & POLLIN)) {
 101         do {
 102             FILLZERO(from);
 103             fromlen=sizeof(from);
 104             BUF_ASSERT_FREE(st->rbuf);
 105             BUF_ALLOC(st->rbuf,"udp_afterpoll");
 106             buffer_init(st->rbuf,calculate_max_start_pad());
 107             rv=recvfrom(st->fd, st->rbuf->start, st->rbuf->len, 0,
 108                         (struct sockaddr *)&from, &fromlen);
 109             if (rv>0) {
 110                 st->rbuf->size=rv;
 111                 if (st->use_proxy) {
 112                     /* Check that the packet came from our poxy server;
 113                        we shouldn't be contacted directly by anybody else
 114                        (since they can trivially forge source addresses) */
 115                     if (memcmp(&from.sin_addr,&st->proxy.sin_addr,4)!=0 ||
 116                         memcmp(&from.sin_port,&st->proxy.sin_port,2)!=0) {
 117                         Message(M_INFO,"udp: received packet that's not "
 118                                 "from the proxy\n");
 119                         BUF_FREE(st->rbuf);
 120                         continue;
 121                     }
 122                     memcpy(&from.sin_addr,buf_unprepend(st->rbuf,4),4);
 123                     buf_unprepend(st->rbuf,2);
 124                     memcpy(&from.sin_port,buf_unprepend(st->rbuf,2),2);
 125                 }
 126                 struct comm_addr ca;
 127                 FILLZERO(ca);
 128                 ca.comm=&st->ops;
 129                 ca.sin=from;
 130                 done=False;
 131                 for (n=st->notify; n; n=n->next) {
 132                     if (n->fn(n->state, st->rbuf, &ca)) {
 133                         done=True;
 134                         break;
 135                     }
 136                 }
 137                 if (!done) {
 138                     uint32_t msgtype;
 139                     if (st->rbuf->size>12 /* prevents traffic amplification */
 140                         && ((msgtype=get_uint32(st->rbuf->start+8))
 141                             != LABEL_NAK)) {
 142                         uint32_t source,dest;
 143                         /* Manufacture and send NAK packet */
 144                         source=get_uint32(st->rbuf->start); /* Us */
 145                         dest=get_uint32(st->rbuf->start+4); /* Them */
 146                         send_nak(&ca,source,dest,msgtype,st->rbuf,"unwanted");
 147                     }
 148                     BUF_FREE(st->rbuf);
 149                 }
 150                 BUF_ASSERT_FREE(st->rbuf);
 151             } else {
 152                 BUF_FREE(st->rbuf);
 153             }
 154         } while (rv>=0);
 155     }
 156 }
 157
 158 static void request_notify(void *commst, void *nst, comm_notify_fn *fn)
 159 {
 160     struct udp *st=commst;
 161     struct notify_list *n;
 162
 163     n=safe_malloc(sizeof(*n),"request_notify");
 164     n->fn=fn;
 165     n->state=nst;
 166     n->next=st->notify;
 167     st->notify=n;
 168 }
 169
 170 static void release_notify(void *commst, void *nst, comm_notify_fn *fn)
 171 {
 172     struct udp *st=commst;
 173     struct notify_list *n, **p, *t;
 174
 175     /* XXX untested */
 176     p=&st->notify;
 177     for (n=st->notify; n; )
 178     {
 179         if (n->state==nst && n->fn==fn) {
 180             t=n;
 181             *p=n->next;
 182             n=n->next;
 183             free(t);
 184         } else {
 185             p=&n->next;
 186             n=n->next;
 187         }
 188     }
 189 }
 190
 191 static bool_t udp_sendmsg(void *commst, struct buffer_if *buf,
 192                           const struct comm_addr *dest)
 193 {
 194     struct udp *st=commst;
 195     uint8_t *sa;
 196
 197     if (st->use_proxy) {
 198         sa=buf_prepend(buf,8);
 199         memcpy(sa,&dest->sin.sin_addr,4);
 200         memset(sa+4,0,4);
 201         memcpy(sa+6,&dest->sin.sin_port,2);
 202         sendto(st->fd,sa,buf->size+8,0,(struct sockaddr *)&st->proxy,
 203                sizeof(st->proxy));
 204         buf_unprepend(buf,8);
 205     } else {
 206         sendto(st->fd, buf->start, buf->size, 0,
 207                (struct sockaddr *)&dest->sin, sizeof(dest->sin));
 208     }
 209
 210     return True;
 211 }
 212
 213 static void udp_phase_hook(void *sst, uint32_t new_phase)
 214 {
 215     struct udp *st=sst;
 216     struct sockaddr_in addr;
 217
 218     st->fd=socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 219     if (st->fd<0) {
 220         fatal_perror("udp (%s:%d): socket",st->loc.file,st->loc.line);
 221     }
 222     if (fcntl(st->fd, F_SETFL, fcntl(st->fd, F_GETFL)|O_NONBLOCK)==-1) {
 223         fatal_perror("udp (%s:%d): fcntl(set O_NONBLOCK)",
 224                      st->loc.file,st->loc.line);
 225     }
 226     if (fcntl(st->fd, F_SETFD, FD_CLOEXEC)==-1) {
 227         fatal_perror("udp (%s:%d): fcntl(set FD_CLOEXEC)",
 228                      st->loc.file,st->loc.line);
 229     }
 230
 231     FILLZERO(addr);
 232     addr.sin_family=AF_INET;
 233     addr.sin_addr.s_addr=htonl(st->addr);
 234     addr.sin_port=htons(st->port);
 235     if (st->authbind) {
 236         pid_t c;
 237         int status;
 238
 239         /* XXX this fork() and waitpid() business needs to be hidden
 240            in some system-specific library functions. */
 241         c=fork();
 242         if (c==-1) {
 243             fatal_perror("udp_phase_hook: fork() for authbind");
 244         }
 245         if (c==0) {
 246             char *argv[4], addrstr[9], portstr[5];
 247             sprintf(addrstr,"%08lX",(long)addr.sin_addr.s_addr);
 248             sprintf(portstr,"%04X",addr.sin_port);
 249             argv[0]=st->authbind;
 250             argv[1]=addrstr;
 251             argv[2]=portstr;
 252             argv[3]=NULL;
 253             dup2(st->fd,0);
 254             execvp(st->authbind,argv);
 255             _exit(255);
 256         }
 257         while (waitpid(c,&status,0)==-1) {
 258             if (errno==EINTR) continue;
 259             fatal_perror("udp (%s:%d): authbind",st->loc.file,st->loc.line);
 260         }
 261         if (WIFSIGNALED(status)) {
 262             fatal("udp (%s:%d): authbind died on signal %d",st->loc.file,
 263                   st->loc.line, WTERMSIG(status));
 264         }
 265         if (WIFEXITED(status) && WEXITSTATUS(status)!=0) {
 266             fatal("udp (%s:%d): authbind died with status %d",st->loc.file,
 267                   st->loc.line, WEXITSTATUS(status));
 268         }
 269     } else {
 270         if (bind(st->fd, (struct sockaddr *)&addr, sizeof(addr))!=0) {
 271             fatal_perror("udp (%s:%d): bind",st->loc.file,st->loc.line);
 272         }
 273     }
 274
 275     register_for_poll(st,udp_beforepoll,udp_afterpoll,1,"udp");
 276 }
 277
 278 static list_t *udp_apply(closure_t *self, struct cloc loc, dict_t *context,
 279                          list_t *args)
 280 {
 281     struct udp *st;
 282     item_t *i,*j;
 283     dict_t *d;
 284     list_t *l;
 285     uint32_t a;
 286
 287     st=safe_malloc(sizeof(*st),"udp_apply(st)");
 288     st->loc=loc;
 289     st->cl.description="udp";
 290     st->cl.type=CL_COMM;
 291     st->cl.apply=NULL;
 292     st->cl.interface=&st->ops;
 293     st->ops.st=st;
 294     st->ops.request_notify=request_notify;
 295     st->ops.release_notify=release_notify;
 296     st->ops.sendmsg=udp_sendmsg;
 297     st->ops.addr_to_string=addr_to_string;
 298     st->port=0;
 299     st->use_proxy=False;
 300
 301     i=list_elem(args,0);
 302     if (!i || i->type!=t_dict) {
 303         cfgfatal(st->loc,"udp","first argument must be a dictionary\n");
 304     }
 305     d=i->data.dict;
 306
 307     j=dict_find_item(d,"address",False,"udp",st->loc);
 308     st->addr=j?string_item_to_ipaddr(j, "udp"):INADDR_ANY;
 309     st->port=dict_read_number(d,"port",True,"udp",st->loc,0);
 310     st->rbuf=find_cl_if(d,"buffer",CL_BUFFER,True,"udp",st->loc);
 311     st->authbind=dict_read_string(d,"authbind",False,"udp",st->loc);
 312     l=dict_lookup(d,"proxy");
 313     if (l) {
 314         st->use_proxy=True;
 315         FILLZERO(st->proxy);
 316         st->proxy.sin_family=AF_INET;
 317         i=list_elem(l,0);
 318         if (!i || i->type!=t_string) {
 319             cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
 320         }
 321         a=string_item_to_ipaddr(i,"proxy");
 322         st->proxy.sin_addr.s_addr=htonl(a);
 323         i=list_elem(l,1);
 324         if (!i || i->type!=t_number) {
 325             cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
 326         }
 327         st->proxy.sin_port=htons(i->data.number);
 328     }
 329
 330     update_max_start_pad(&comm_max_start_pad, st->use_proxy ? 8 : 0);
 331
 332     add_hook(PHASE_GETRESOURCES,udp_phase_hook,st);
 333
 334     return new_closure(&st->cl);
 335 }
 336
 337 void udp_module(dict_t *dict)
 338 {
 339     add_closure(dict,"udp",udp_apply);
 340 }