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