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 "util.h"
  20 #include "unaligned.h"
  21 #include "ipaddr.h"
  22
  23 static beforepoll_fn udp_beforepoll;
  24 static afterpoll_fn udp_afterpoll;
  25 static comm_request_notify_fn request_notify;
  26 static comm_release_notify_fn release_notify;
  27 static comm_sendmsg_fn udp_sendmsg;
  28
  29 struct notify_list {
  30     comm_notify_fn *fn;
  31     void *state;
  32     struct notify_list *next;
  33 };
  34
  35 struct udp {
  36     closure_t cl;
  37     struct comm_if ops;
  38     struct cloc loc;
  39     uint16_t port;
  40     int fd;
  41     string_t authbind;
  42     struct buffer_if *rbuf;
  43     struct notify_list *notify;
  44     bool_t use_proxy;
  45     struct sockaddr_in proxy;
  46 };
  47
  48 static int udp_beforepoll(void *state, struct pollfd *fds, int *nfds_io,
  49                           int *timeout_io, const struct timeval *tv,
  50                           uint64_t *now)
  51 {
  52     struct udp *st=state;
  53     if (*nfds_io<1) {
  54         *nfds_io=1;
  55         return ERANGE;
  56     }
  57     *nfds_io=1;
  58     fds->fd=st->fd;
  59     fds->events=POLLIN;
  60     return 0;
  61 }
  62
  63 static void udp_afterpoll(void *state, struct pollfd *fds, int nfds,
  64                           const struct timeval *tv, uint64_t *now)
  65 {
  66     struct udp *st=state;
  67     struct sockaddr_in from;
  68     int fromlen;
  69     struct notify_list *n;
  70     bool_t done;
  71     int rv;
  72
  73     if (nfds && (fds->revents & POLLIN)) {
  74         do {
  75             fromlen=sizeof(from);
  76             BUF_ASSERT_FREE(st->rbuf);
  77             BUF_ALLOC(st->rbuf,"udp_afterpoll");
  78             rv=recvfrom(st->fd, st->rbuf->start, st->rbuf->len, 0,
  79                         (struct sockaddr *)&from, &fromlen);
  80             if (rv>0) {
  81                 st->rbuf->size=rv;
  82                 if (st->use_proxy) {
  83                     /* Check that the packet came from our poxy server;
  84                        we shouldn't be contacted directly by anybody else
  85                        (since they can trivially forge source addresses) */
  86                     if (memcmp(&from.sin_addr,&st->proxy.sin_addr,4)!=0 ||
  87                         memcmp(&from.sin_port,&st->proxy.sin_port,2)!=0) {
  88                         Message(M_INFO,"udp: received packet that's not "
  89                                 "from the proxy\n");
  90                         BUF_FREE(st->rbuf);
  91                         continue;
  92                     }
  93                     memcpy(&from.sin_addr,buf_unprepend(st->rbuf,4),4);
  94                     buf_unprepend(st->rbuf,2);
  95                     memcpy(&from.sin_port,buf_unprepend(st->rbuf,2),2);
  96                 }
  97                 done=False;
  98                 for (n=st->notify; n; n=n->next) {
  99                     if (n->fn(n->state, st->rbuf, &from)) {
 100                         done=True;
 101                         break;
 102                     }
 103                 }
 104                 if (!done) {
 105                     uint32_t source,dest;
 106                     /* Manufacture and send NAK packet */
 107                     source=get_uint32(st->rbuf->start); /* Us */
 108                     dest=get_uint32(st->rbuf->start+4); /* Them */
 109                     Message(M_INFO,"udp (port %d): sending NAK\n",st->port);
 110                     buffer_init(st->rbuf,0);
 111                     buf_append_uint32(st->rbuf,dest);
 112                     buf_append_uint32(st->rbuf,source);
 113                     buf_append_uint32(st->rbuf,0); /* NAK is msg type 0 */
 114                     sendto(st->fd, st->rbuf->start, st->rbuf->size, 0,
 115                            (struct sockaddr *)&from, sizeof(from));
 116                     BUF_FREE(st->rbuf);
 117                 }
 118                 BUF_ASSERT_FREE(st->rbuf);
 119             } else {
 120                 BUF_FREE(st->rbuf);
 121             }
 122         } while (rv>=0);
 123     }
 124 }
 125
 126 static void request_notify(void *commst, void *nst, comm_notify_fn *fn)
 127 {
 128     struct udp *st=commst;
 129     struct notify_list *n;
 130
 131     n=safe_malloc(sizeof(*n),"request_notify");
 132     n->fn=fn;
 133     n->state=nst;
 134     n->next=st->notify;
 135     st->notify=n;
 136 }
 137
 138 static void release_notify(void *commst, void *nst, comm_notify_fn *fn)
 139 {
 140     struct udp *st=commst;
 141     struct notify_list *n, **p, *t;
 142
 143     /* XXX untested */
 144     p=&st->notify;
 145     for (n=st->notify; n; )
 146     {
 147         if (n->state==nst && n->fn==fn) {
 148             t=n;
 149             *p=n->next;
 150             n=n->next;
 151             free(t);
 152         } else {
 153             p=&n->next;
 154             n=n->next;
 155         }
 156     }
 157 }
 158
 159 static bool_t udp_sendmsg(void *commst, struct buffer_if *buf,
 160                           struct sockaddr_in *dest)
 161 {
 162     struct udp *st=commst;
 163     uint8_t *sa;
 164
 165     if (st->use_proxy) {
 166         sa=buf->start-8;
 167         memcpy(sa,&dest->sin_addr,4);
 168         memset(sa+4,0,4);
 169         memcpy(sa+6,&dest->sin_port,2);
 170         sendto(st->fd,sa,buf->size+8,0,(struct sockaddr *)&st->proxy,
 171                sizeof(st->proxy));
 172     } else {
 173         sendto(st->fd, buf->start, buf->size, 0,
 174                (struct sockaddr *)dest, sizeof(*dest));
 175     }
 176
 177     return True;
 178 }
 179
 180 static void udp_phase_hook(void *sst, uint32_t new_phase)
 181 {
 182     struct udp *st=sst;
 183     struct sockaddr_in addr;
 184
 185     st->fd=socket(AF_INET, SOCK_DGRAM, 0);
 186     if (st->fd<0) {
 187         fatal_perror("udp (%s:%d): socket",st->loc.file,st->loc.line);
 188     }
 189     if (fcntl(st->fd, F_SETFL, fcntl(st->fd, F_GETFL)|O_NONBLOCK)==-1) {
 190         fatal_perror("udp (%s:%d): fcntl(set O_NONBLOCK)",
 191                      st->loc.file,st->loc.line);
 192     }
 193     if (fcntl(st->fd, F_SETFD, FD_CLOEXEC)==-1) {
 194         fatal_perror("udp (%s:%d): fcntl(set FD_CLOEXEC)",
 195                      st->loc.file,st->loc.line);
 196     }
 197
 198     memset(&addr, 0, sizeof(addr));
 199     addr.sin_family=AF_INET;
 200     addr.sin_port=htons(st->port);
 201     if (st->authbind) {
 202         pid_t c;
 203         int status;
 204
 205         /* XXX this fork() and waitpid() business needs to be hidden
 206            in some system-specific library functions. */
 207         c=fork();
 208         if (c==-1) {
 209             fatal_perror("udp_phase_hook: fork() for authbind");
 210         }
 211         if (c==0) {
 212             char *argv[4];
 213             argv[0]=st->authbind;
 214             argv[1]="00000000";
 215             argv[2]=alloca(8);
 216             if (!argv[2]) exit(ENOMEM);
 217             sprintf(argv[2],"%04X",htons(st->port));
 218             argv[3]=NULL;
 219             dup2(st->fd,0);
 220             execvp(st->authbind,argv);
 221             exit(ENOEXEC);
 222         }
 223         waitpid(c,&status,0);
 224         if (WEXITSTATUS(status)!=0) {
 225             errno=WEXITSTATUS(status);
 226             fatal_perror("udp (%s:%d): authbind",st->loc.file,st->loc.line);
 227         }
 228     } else {
 229         if (bind(st->fd, (struct sockaddr *)&addr, sizeof(addr))!=0) {
 230             fatal_perror("udp (%s:%d): bind",st->loc.file,st->loc.line);
 231         }
 232     }
 233
 234     register_for_poll(st,udp_beforepoll,udp_afterpoll,1,"udp");
 235 }
 236
 237 static list_t *udp_apply(closure_t *self, struct cloc loc, dict_t *context,
 238                          list_t *args)
 239 {
 240     struct udp *st;
 241     item_t *i;
 242     dict_t *d;
 243     list_t *l;
 244     uint32_t a;
 245
 246     st=safe_malloc(sizeof(*st),"udp_apply(st)");
 247     st->loc=loc;
 248     st->cl.description="udp";
 249     st->cl.type=CL_COMM;
 250     st->cl.apply=NULL;
 251     st->cl.interface=&st->ops;
 252     st->ops.st=st;
 253     st->ops.min_start_pad=0;
 254     st->ops.min_end_pad=0;
 255     st->ops.request_notify=request_notify;
 256     st->ops.release_notify=release_notify;
 257     st->ops.sendmsg=udp_sendmsg;
 258     st->port=0;
 259     st->use_proxy=False;
 260
 261     i=list_elem(args,0);
 262     if (!i || i->type!=t_dict) {
 263         cfgfatal(st->loc,"udp","first argument must be a dictionary\n");
 264     }
 265     d=i->data.dict;
 266
 267     st->port=dict_read_number(d,"port",True,"udp",st->loc,0);
 268     st->rbuf=find_cl_if(d,"buffer",CL_BUFFER,True,"udp",st->loc);
 269     st->authbind=dict_read_string(d,"authbind",False,"udp",st->loc);
 270     l=dict_lookup(d,"proxy");
 271     if (l) {
 272         st->use_proxy=True;
 273         memset(&st->proxy,0,sizeof(st->proxy));
 274         st->proxy.sin_family=AF_INET;
 275         i=list_elem(l,0);
 276         if (!i || i->type!=t_string) {
 277             cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
 278         }
 279         a=string_item_to_ipaddr(i,"proxy");
 280         st->proxy.sin_addr.s_addr=htonl(a);
 281         i=list_elem(l,1);
 282         if (!i || i->type!=t_number) {
 283             cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
 284         }
 285         st->proxy.sin_port=htons(i->data.number);
 286         st->ops.min_start_pad=8;
 287     }
 288
 289     add_hook(PHASE_GETRESOURCES,udp_phase_hook,st);
 290
 291     return new_closure(&st->cl);
 292 }
 293
 294 init_module udp_module;
 295 void udp_module(dict_t *dict)
 296 {
 297     add_closure(dict,"udp",udp_apply);
 298 }