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