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     union iaddr addr;
  44     int fd;
  45     string_t authbind;
  46     struct buffer_if *rbuf;
  47     struct notify_list *notify;
  48     bool_t use_proxy;
  49     union iaddr proxy;
  50 };
  51
  52 static const char *addr_to_string(void *commst, const struct comm_addr *ca) {
  53     struct udp *st=commst;
  54     static char sbuf[100];
  55
  56     snprintf(sbuf, sizeof(sbuf), "udp:%s-%s",
  57             iaddr_to_string(&st->addr), iaddr_to_string(&ca->ia));
  58     return sbuf;
  59 }
  60
  61 static int udp_beforepoll(void *state, struct pollfd *fds, int *nfds_io,
  62                           int *timeout_io)
  63 {
  64     struct udp *st=state;
  65     if (*nfds_io<1) {
  66         *nfds_io=1;
  67         return ERANGE;
  68     }
  69     *nfds_io=1;
  70     fds->fd=st->fd;
  71     fds->events=POLLIN;
  72     return 0;
  73 }
  74
  75 static void udp_afterpoll(void *state, struct pollfd *fds, int nfds)
  76 {
  77     struct udp *st=state;
  78     union iaddr from;
  79     socklen_t fromlen;
  80     struct notify_list *n;
  81     bool_t done;
  82     int rv;
  83
  84     if (nfds && (fds->revents & POLLIN)) {
  85         do {
  86             FILLZERO(from);
  87             fromlen=sizeof(from);
  88             BUF_ASSERT_FREE(st->rbuf);
  89             BUF_ALLOC(st->rbuf,"udp_afterpoll");
  90             buffer_init(st->rbuf,calculate_max_start_pad());
  91             rv=recvfrom(st->fd, st->rbuf->start,
  92                         buf_remaining_space(st->rbuf),
  93                         0, (struct sockaddr *)&from, &fromlen);
  94             if (rv>0) {
  95                 st->rbuf->size=rv;
  96                 if (st->use_proxy) {
  97                     /* Check that the packet came from our poxy server;
  98                        we shouldn't be contacted directly by anybody else
  99                        (since they can trivially forge source addresses) */
 100                     if (!iaddr_equal(&from,&st->proxy)) {
 101                         Message(M_INFO,"udp: received packet that's not "
 102                                 "from the proxy\n");
 103                         BUF_FREE(st->rbuf);
 104                         continue;
 105                     }
 106                     /* proxy protocol supports ipv4 transport only */
 107                     FILLZERO(from);
 108                     from.sa.sa_family=AF_INET;
 109                     memcpy(&from.sin.sin_addr,buf_unprepend(st->rbuf,4),4);
 110                     buf_unprepend(st->rbuf,2);
 111                     memcpy(&from.sin.sin_port,buf_unprepend(st->rbuf,2),2);
 112                 }
 113                 struct comm_addr ca;
 114                 FILLZERO(ca);
 115                 ca.comm=&st->ops;
 116                 ca.ia=from;
 117                 done=False;
 118                 for (n=st->notify; n; n=n->next) {
 119                     if (n->fn(n->state, st->rbuf, &ca)) {
 120                         done=True;
 121                         break;
 122                     }
 123                 }
 124                 if (!done) {
 125                     uint32_t msgtype;
 126                     if (st->rbuf->size>12 /* prevents traffic amplification */
 127                         && ((msgtype=get_uint32(st->rbuf->start+8))
 128                             != LABEL_NAK)) {
 129                         uint32_t source,dest;
 130                         /* Manufacture and send NAK packet */
 131                         source=get_uint32(st->rbuf->start); /* Us */
 132                         dest=get_uint32(st->rbuf->start+4); /* Them */
 133                         send_nak(&ca,source,dest,msgtype,st->rbuf,"unwanted");
 134                     }
 135                     BUF_FREE(st->rbuf);
 136                 }
 137                 BUF_ASSERT_FREE(st->rbuf);
 138             } else {
 139                 BUF_FREE(st->rbuf);
 140             }
 141         } while (rv>=0);
 142     }
 143 }
 144
 145 static void request_notify(void *commst, void *nst, comm_notify_fn *fn)
 146 {
 147     struct udp *st=commst;
 148     struct notify_list *n;
 149
 150     n=safe_malloc(sizeof(*n),"request_notify");
 151     n->fn=fn;
 152     n->state=nst;
 153     n->next=st->notify;
 154     st->notify=n;
 155 }
 156
 157 static void release_notify(void *commst, void *nst, comm_notify_fn *fn)
 158 {
 159     struct udp *st=commst;
 160     struct notify_list *n, **p, *t;
 161
 162     /* XXX untested */
 163     p=&st->notify;
 164     for (n=st->notify; n; )
 165     {
 166         if (n->state==nst && n->fn==fn) {
 167             t=n;
 168             *p=n->next;
 169             n=n->next;
 170             free(t);
 171         } else {
 172             p=&n->next;
 173             n=n->next;
 174         }
 175     }
 176 }
 177
 178 static bool_t udp_sendmsg(void *commst, struct buffer_if *buf,
 179                           const struct comm_addr *dest)
 180 {
 181     struct udp *st=commst;
 182     uint8_t *sa;
 183
 184     if (st->use_proxy) {
 185         sa=buf_prepend(buf,8);
 186         if (dest->ia.sa.sa_family != AF_INET) {
 187             Message(M_INFO,
 188                "udp: proxy means dropping outgoing non-IPv4 packet to %s\n",
 189                     iaddr_to_string(&dest->ia));
 190             return False;
 191         }
 192         memcpy(sa,&dest->ia.sin.sin_addr,4);
 193         memset(sa+4,0,4);
 194         memcpy(sa+6,&dest->ia.sin.sin_port,2);
 195         sendto(st->fd,sa,buf->size+8,0,(struct sockaddr *)&st->proxy,
 196                sizeof(st->proxy));
 197         buf_unprepend(buf,8);
 198     } else {
 199         sendto(st->fd, buf->start, buf->size, 0,
 200                &dest->ia.sa, iaddr_socklen(&dest->ia));
 201     }
 202
 203     return True;
 204 }
 205
 206 static void udp_phase_hook(void *sst, uint32_t new_phase)
 207 {
 208     struct udp *st=sst;
 209     union iaddr addr;
 210
 211     st->fd=socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
 212     if (st->fd<0) {
 213         fatal_perror("udp (%s:%d): socket",st->loc.file,st->loc.line);
 214     }
 215     if (fcntl(st->fd, F_SETFL, fcntl(st->fd, F_GETFL)|O_NONBLOCK)==-1) {
 216         fatal_perror("udp (%s:%d): fcntl(set O_NONBLOCK)",
 217                      st->loc.file,st->loc.line);
 218     }
 219     setcloexec(st->fd);
 220
 221     addr=st->addr;
 222     if (st->authbind) {
 223         pid_t c;
 224         int status;
 225
 226         /* XXX this fork() and waitpid() business needs to be hidden
 227            in some system-specific library functions. */
 228         c=fork();
 229         if (c==-1) {
 230             fatal_perror("udp_phase_hook: fork() for authbind");
 231         }
 232         if (c==0) {
 233             char *argv[4], addrstr[9], portstr[5];
 234             switch (addr.sa.sa_family) {
 235             case AF_INET:
 236                 sprintf(addrstr,"%08lX",(long)addr.sin.sin_addr.s_addr);
 237                 sprintf(portstr,"%04X",addr.sin.sin_port);
 238                 break;
 239             default:
 240                 fatal("udp (%s:%d): unsupported address family for authbind",
 241                       st->loc.file,st->loc.line);
 242             }
 243             argv[0]=st->authbind;
 244             argv[1]=addrstr;
 245             argv[2]=portstr;
 246             argv[3]=NULL;
 247             dup2(st->fd,0);
 248             execvp(st->authbind,argv);
 249             _exit(255);
 250         }
 251         while (waitpid(c,&status,0)==-1) {
 252             if (errno==EINTR) continue;
 253             fatal_perror("udp (%s:%d): authbind",st->loc.file,st->loc.line);
 254         }
 255         if (WIFSIGNALED(status)) {
 256             fatal("udp (%s:%d): authbind died on signal %d",st->loc.file,
 257                   st->loc.line, WTERMSIG(status));
 258         }
 259         if (WIFEXITED(status) && WEXITSTATUS(status)!=0) {
 260             fatal("udp (%s:%d): authbind died with status %d",st->loc.file,
 261                   st->loc.line, WEXITSTATUS(status));
 262         }
 263     } else {
 264         if (bind(st->fd, (struct sockaddr *)&addr, sizeof(addr))!=0) {
 265             fatal_perror("udp (%s:%d): bind",st->loc.file,st->loc.line);
 266         }
 267     }
 268
 269     register_for_poll(st,udp_beforepoll,udp_afterpoll,1,"udp");
 270 }
 271
 272 static list_t *udp_apply(closure_t *self, struct cloc loc, dict_t *context,
 273                          list_t *args)
 274 {
 275     struct udp *st;
 276     item_t *i,*j;
 277     dict_t *d;
 278     list_t *l;
 279     uint32_t a;
 280
 281     st=safe_malloc(sizeof(*st),"udp_apply(st)");
 282     st->loc=loc;
 283     st->cl.description="udp";
 284     st->cl.type=CL_COMM;
 285     st->cl.apply=NULL;
 286     st->cl.interface=&st->ops;
 287     st->ops.st=st;
 288     st->ops.request_notify=request_notify;
 289     st->ops.release_notify=release_notify;
 290     st->ops.sendmsg=udp_sendmsg;
 291     st->ops.addr_to_string=addr_to_string;
 292     FILLZERO(st->addr);
 293     st->use_proxy=False;
 294
 295     i=list_elem(args,0);
 296     if (!i || i->type!=t_dict) {
 297         cfgfatal(st->loc,"udp","first argument must be a dictionary\n");
 298     }
 299     d=i->data.dict;
 300
 301     st->addr.sa.sa_family=AF_INET;
 302     j=dict_find_item(d,"address",False,"udp",st->loc);
 303     st->addr.sin.sin_addr.s_addr=j?string_item_to_ipaddr(j, "udp"):INADDR_ANY;
 304     st->addr.sin.sin_port=dict_read_number(d,"port",True,"udp",st->loc,0);
 305     st->rbuf=find_cl_if(d,"buffer",CL_BUFFER,True,"udp",st->loc);
 306     st->authbind=dict_read_string(d,"authbind",False,"udp",st->loc);
 307     l=dict_lookup(d,"proxy");
 308     if (l) {
 309         st->use_proxy=True;
 310         FILLZERO(st->proxy);
 311         st->proxy.sa.sa_family=AF_INET;
 312         i=list_elem(l,0);
 313         if (!i || i->type!=t_string) {
 314             cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
 315         }
 316         a=string_item_to_ipaddr(i,"proxy");
 317         st->proxy.sin.sin_addr.s_addr=htonl(a);
 318         i=list_elem(l,1);
 319         if (!i || i->type!=t_number) {
 320             cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
 321         }
 322         st->proxy.sin.sin_port=htons(i->data.number);
 323     }
 324
 325     update_max_start_pad(&comm_max_start_pad, st->use_proxy ? 8 : 0);
 326
 327     add_hook(PHASE_GETRESOURCES,udp_phase_hook,st);
 328
 329     return new_closure(&st->cl);
 330 }
 331
 332 void udp_module(dict_t *dict)
 333 {
 334     add_closure(dict,"udp",udp_apply);
 335 }