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             buffer_init(st->rbuf,calculate_max_start_pad());
 106             rv=recvfrom(st->fd, st->rbuf->start, st->rbuf->len, 0,
 107                         (struct sockaddr *)&from, &fromlen);
 108             if (rv>0) {
 109                 st->rbuf->size=rv;
 110                 if (st->use_proxy) {
 111                     /* Check that the packet came from our poxy server;
 112                        we shouldn't be contacted directly by anybody else
 113                        (since they can trivially forge source addresses) */
 114                     if (memcmp(&from.sin_addr,&st->proxy.sin_addr,4)!=0 ||
 115                         memcmp(&from.sin_port,&st->proxy.sin_port,2)!=0) {
 116                         Message(M_INFO,"udp: received packet that's not "
 117                                 "from the proxy\n");
 118                         BUF_FREE(st->rbuf);
 119                         continue;
 120                     }
 121                     memcpy(&from.sin_addr,buf_unprepend(st->rbuf,4),4);
 122                     buf_unprepend(st->rbuf,2);
 123                     memcpy(&from.sin_port,buf_unprepend(st->rbuf,2),2);
 124                 }
 125                 struct comm_addr ca;
 126                 FILLZERO(ca);
 127                 ca.comm=&st->ops;
 128                 ca.sin=from;
 129                 done=False;
 130                 for (n=st->notify; n; n=n->next) {
 131                     if (n->fn(n->state, st->rbuf, &ca)) {
 132                         done=True;
 133                         break;
 134                     }
 135                 }
 136                 if (!done) {
 137                     uint32_t msgtype;
 138                     if (st->rbuf->size>12 /* prevents traffic amplification */
 139                         && ((msgtype=get_uint32(st->rbuf->start+8))
 140                             != LABEL_NAK)) {
 141                         uint32_t source,dest;
 142                         /* Manufacture and send NAK packet */
 143                         source=get_uint32(st->rbuf->start); /* Us */
 144                         dest=get_uint32(st->rbuf->start+4); /* Them */
 145                         send_nak(&ca,source,dest,msgtype,st->rbuf,"unwanted");
 146                     }
 147                     BUF_FREE(st->rbuf);
 148                 }
 149                 BUF_ASSERT_FREE(st->rbuf);
 150             } else {
 151                 BUF_FREE(st->rbuf);
 152             }
 153         } while (rv>=0);
 154     }
 155 }
 156
 157 static void request_notify(void *commst, void *nst, comm_notify_fn *fn)
 158 {
 159     struct udp *st=commst;
 160     struct notify_list *n;
 161
 162     n=safe_malloc(sizeof(*n),"request_notify");
 163     n->fn=fn;
 164     n->state=nst;
 165     n->next=st->notify;
 166     st->notify=n;
 167 }
 168
 169 static void release_notify(void *commst, void *nst, comm_notify_fn *fn)
 170 {
 171     struct udp *st=commst;
 172     struct notify_list *n, **p, *t;
 173
 174     /* XXX untested */
 175     p=&st->notify;
 176     for (n=st->notify; n; )
 177     {
 178         if (n->state==nst && n->fn==fn) {
 179             t=n;
 180             *p=n->next;
 181             n=n->next;
 182             free(t);
 183         } else {
 184             p=&n->next;
 185             n=n->next;
 186         }
 187     }
 188 }
 189
 190 static bool_t udp_sendmsg(void *commst, struct buffer_if *buf,
 191                           const struct comm_addr *dest)
 192 {
 193     struct udp *st=commst;
 194     uint8_t *sa;
 195
 196     if (st->use_proxy) {
 197         sa=buf_prepend(buf,8);
 198         memcpy(sa,&dest->sin.sin_addr,4);
 199         memset(sa+4,0,4);
 200         memcpy(sa+6,&dest->sin.sin_port,2);
 201         sendto(st->fd,sa,buf->size+8,0,(struct sockaddr *)&st->proxy,
 202                sizeof(st->proxy));
 203         buf_unprepend(buf,8);
 204     } else {
 205         sendto(st->fd, buf->start, buf->size, 0,
 206                (struct sockaddr *)&dest->sin, sizeof(dest->sin));
 207     }
 208
 209     return True;
 210 }
 211
 212 static void udp_phase_hook(void *sst, uint32_t new_phase)
 213 {
 214     struct udp *st=sst;
 215     struct sockaddr_in addr;
 216
 217     st->fd=socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 218     if (st->fd<0) {
 219         fatal_perror("udp (%s:%d): socket",st->loc.file,st->loc.line);
 220     }
 221     if (fcntl(st->fd, F_SETFL, fcntl(st->fd, F_GETFL)|O_NONBLOCK)==-1) {
 222         fatal_perror("udp (%s:%d): fcntl(set O_NONBLOCK)",
 223                      st->loc.file,st->loc.line);
 224     }
 225     if (fcntl(st->fd, F_SETFD, FD_CLOEXEC)==-1) {
 226         fatal_perror("udp (%s:%d): fcntl(set FD_CLOEXEC)",
 227                      st->loc.file,st->loc.line);
 228     }
 229
 230     FILLZERO(addr);
 231     addr.sin_family=AF_INET;
 232     addr.sin_addr.s_addr=htonl(st->addr);
 233     addr.sin_port=htons(st->port);
 234     if (st->authbind) {
 235         pid_t c;
 236         int status;
 237
 238         /* XXX this fork() and waitpid() business needs to be hidden
 239            in some system-specific library functions. */
 240         c=fork();
 241         if (c==-1) {
 242             fatal_perror("udp_phase_hook: fork() for authbind");
 243         }
 244         if (c==0) {
 245             char *argv[4], addrstr[9], portstr[5];
 246             sprintf(addrstr,"%08lX",(long)addr.sin_addr.s_addr);
 247             sprintf(portstr,"%04X",addr.sin_port);
 248             argv[0]=st->authbind;
 249             argv[1]=addrstr;
 250             argv[2]=portstr;
 251             argv[3]=NULL;
 252             dup2(st->fd,0);
 253             execvp(st->authbind,argv);
 254             _exit(255);
 255         }
 256         while (waitpid(c,&status,0)==-1) {
 257             if (errno==EINTR) continue;
 258             fatal_perror("udp (%s:%d): authbind",st->loc.file,st->loc.line);
 259         }
 260         if (WIFSIGNALED(status)) {
 261             fatal("udp (%s:%d): authbind died on signal %d",st->loc.file,
 262                   st->loc.line, WTERMSIG(status));
 263         }
 264         if (WIFEXITED(status) && WEXITSTATUS(status)!=0) {
 265             fatal("udp (%s:%d): authbind died with status %d",st->loc.file,
 266                   st->loc.line, WEXITSTATUS(status));
 267         }
 268     } else {
 269         if (bind(st->fd, (struct sockaddr *)&addr, sizeof(addr))!=0) {
 270             fatal_perror("udp (%s:%d): bind",st->loc.file,st->loc.line);
 271         }
 272     }
 273
 274     register_for_poll(st,udp_beforepoll,udp_afterpoll,1,"udp");
 275 }
 276
 277 static list_t *udp_apply(closure_t *self, struct cloc loc, dict_t *context,
 278                          list_t *args)
 279 {
 280     struct udp *st;
 281     item_t *i,*j;
 282     dict_t *d;
 283     list_t *l;
 284     uint32_t a;
 285
 286     st=safe_malloc(sizeof(*st),"udp_apply(st)");
 287     st->loc=loc;
 288     st->cl.description="udp";
 289     st->cl.type=CL_COMM;
 290     st->cl.apply=NULL;
 291     st->cl.interface=&st->ops;
 292     st->ops.st=st;
 293     st->ops.request_notify=request_notify;
 294     st->ops.release_notify=release_notify;
 295     st->ops.sendmsg=udp_sendmsg;
 296     st->ops.addr_to_string=addr_to_string;
 297     st->port=0;
 298     st->use_proxy=False;
 299
 300     i=list_elem(args,0);
 301     if (!i || i->type!=t_dict) {
 302         cfgfatal(st->loc,"udp","first argument must be a dictionary\n");
 303     }
 304     d=i->data.dict;
 305
 306     j=dict_find_item(d,"address",False,"udp",st->loc);
 307     st->addr=j?string_item_to_ipaddr(j, "udp"):INADDR_ANY;
 308     st->port=dict_read_number(d,"port",True,"udp",st->loc,0);
 309     st->rbuf=find_cl_if(d,"buffer",CL_BUFFER,True,"udp",st->loc);
 310     st->authbind=dict_read_string(d,"authbind",False,"udp",st->loc);
 311     l=dict_lookup(d,"proxy");
 312     if (l) {
 313         st->use_proxy=True;
 314         FILLZERO(st->proxy);
 315         st->proxy.sin_family=AF_INET;
 316         i=list_elem(l,0);
 317         if (!i || i->type!=t_string) {
 318             cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
 319         }
 320         a=string_item_to_ipaddr(i,"proxy");
 321         st->proxy.sin_addr.s_addr=htonl(a);
 322         i=list_elem(l,1);
 323         if (!i || i->type!=t_number) {
 324             cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
 325         }
 326         st->proxy.sin_port=htons(i->data.number);
 327     }
 328
 329     update_max_start_pad(&comm_max_start_pad, st->use_proxy ? 8 : 0);
 330
 331     add_hook(PHASE_GETRESOURCES,udp_phase_hook,st);
 332
 333     return new_closure(&st->cl);
 334 }
 335
 336 void udp_module(dict_t *dict)
 337 {
 338     add_closure(dict,"udp",udp_apply);
 339 }