chiark / gitweb /
fds: Provide cloexec() and use it in udp.c and tun.c
[secnet.git] / udp.c
diff --git a/udp.c b/udp.c
index f055962..bb82026 100644 (file)
--- a/udp.c
+++ b/udp.c
@@ -5,10 +5,6 @@
  * optionally bind to a particular local IP address (not implemented
  * yet).
  *
- * Sites register an interest in local port numbers for receiving
- * packets, and can also send packets. We don't care about the source
- * port number for sending packets. 
- *
  * Packets are offered to registered receivers in turn. Once one
  * accepts it, it isn't offered to any more. */
 
 #include <string.h>
 #include <errno.h>
 #include <sys/socket.h>
+#include <sys/wait.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
 #include "util.h"
+#include "magic.h"
+#include "unaligned.h"
+#include "ipaddr.h"
+#include "magic.h"
 
 static beforepoll_fn udp_beforepoll;
 static afterpoll_fn udp_afterpoll;
@@ -27,10 +30,6 @@ static comm_request_notify_fn request_notify;
 static comm_release_notify_fn release_notify;
 static comm_sendmsg_fn udp_sendmsg;
 
-/* The UDP module exports a pure closure which can be used to construct a
- * UDP send/receive module. Arguments:
- */
-
 struct notify_list {
     comm_notify_fn *fn;
     void *state;
@@ -41,14 +40,42 @@ struct udp {
     closure_t cl;
     struct comm_if ops;
     struct cloc loc;
+    uint32_t addr;
+    uint16_t port;
     int fd;
+    string_t authbind;
     struct buffer_if *rbuf;
     struct notify_list *notify;
+    bool_t use_proxy;
+    struct sockaddr_in proxy;
 };
 
+static const char *saddr_to_string(const struct sockaddr_in *sin) {
+    static char bufs[2][100];
+    static int b;
+
+    b ^= 1;
+    snprintf(bufs[b], sizeof(bufs[b]), "[%s]:%d",
+            inet_ntoa(sin->sin_addr),
+            ntohs(sin->sin_port));
+    return bufs[b];
+}
+
+static const char *addr_to_string(void *commst, const struct comm_addr *ca) {
+    struct udp *st=commst;
+    static char sbuf[100];
+
+    struct sockaddr_in la;
+    la.sin_addr.s_addr=htonl(st->addr);
+    la.sin_port=htons(st->port);
+
+    snprintf(sbuf, sizeof(sbuf), "udp:%s-%s",
+            saddr_to_string(&la), saddr_to_string(&ca->sin));
+    return sbuf;
+}
+
 static int udp_beforepoll(void *state, struct pollfd *fds, int *nfds_io,
-                         int *timeout_io, const struct timeval *tv,
-                         uint64_t *now)
+                         int *timeout_io)
 {
     struct udp *st=state;
     if (*nfds_io<1) {
@@ -61,35 +88,64 @@ static int udp_beforepoll(void *state, struct pollfd *fds, int *nfds_io,
     return 0;
 }
 
-static void udp_afterpoll(void *state, struct pollfd *fds, int nfds,
-                         const struct timeval *tv, uint64_t *now)
+static void udp_afterpoll(void *state, struct pollfd *fds, int nfds)
 {
     struct udp *st=state;
     struct sockaddr_in from;
-    int fromlen;
+    socklen_t fromlen;
     struct notify_list *n;
     bool_t done;
     int rv;
 
     if (nfds && (fds->revents & POLLIN)) {
        do {
+           FILLZERO(from);
            fromlen=sizeof(from);
            BUF_ASSERT_FREE(st->rbuf);
            BUF_ALLOC(st->rbuf,"udp_afterpoll");
-           rv=recvfrom(st->fd, st->rbuf->start, st->rbuf->len, 0,
-                       (struct sockaddr *)&from, &fromlen);
+           buffer_init(st->rbuf,calculate_max_start_pad());
+           rv=recvfrom(st->fd, st->rbuf->start,
+                       buf_remaining_space(st->rbuf),
+                       0, (struct sockaddr *)&from, &fromlen);
            if (rv>0) {
                st->rbuf->size=rv;
+               if (st->use_proxy) {
+                   /* Check that the packet came from our poxy server;
+                      we shouldn't be contacted directly by anybody else
+                      (since they can trivially forge source addresses) */
+                   if (memcmp(&from.sin_addr,&st->proxy.sin_addr,4)!=0 ||
+                       memcmp(&from.sin_port,&st->proxy.sin_port,2)!=0) {
+                       Message(M_INFO,"udp: received packet that's not "
+                               "from the proxy\n");
+                       BUF_FREE(st->rbuf);
+                       continue;
+                   }
+                   memcpy(&from.sin_addr,buf_unprepend(st->rbuf,4),4);
+                   buf_unprepend(st->rbuf,2);
+                   memcpy(&from.sin_port,buf_unprepend(st->rbuf,2),2);
+               }
+               struct comm_addr ca;
+               FILLZERO(ca);
+               ca.comm=&st->ops;
+               ca.sin=from;
                done=False;
                for (n=st->notify; n; n=n->next) {
-                   if (n->fn(n->state, st->rbuf, &from)) {
+                   if (n->fn(n->state, st->rbuf, &ca)) {
                        done=True;
                        break;
                    }
                }
                if (!done) {
-                   /* XXX manufacture and send NAK packet */
-                   Message(M_WARNING,"Need to send NAK\n");
+                   uint32_t msgtype;
+                   if (st->rbuf->size>12 /* prevents traffic amplification */
+                       && ((msgtype=get_uint32(st->rbuf->start+8))
+                           != LABEL_NAK)) {
+                       uint32_t source,dest;
+                       /* Manufacture and send NAK packet */
+                       source=get_uint32(st->rbuf->start); /* Us */
+                       dest=get_uint32(st->rbuf->start+4); /* Them */
+                       send_nak(&ca,source,dest,msgtype,st->rbuf,"unwanted");
+                   }
                    BUF_FREE(st->rbuf);
                }
                BUF_ASSERT_FREE(st->rbuf);
@@ -134,25 +190,97 @@ static void release_notify(void *commst, void *nst, comm_notify_fn *fn)
 }
 
 static bool_t udp_sendmsg(void *commst, struct buffer_if *buf,
-                         struct sockaddr_in *dest)
+                         const struct comm_addr *dest)
 {
     struct udp *st=commst;
+    uint8_t *sa;
 
-    /* XXX fix error reporting */
-    sendto(st->fd, buf->start, buf->size, 0,
-          (struct sockaddr *)dest, sizeof(*dest));
+    if (st->use_proxy) {
+       sa=buf_prepend(buf,8);
+       memcpy(sa,&dest->sin.sin_addr,4);
+       memset(sa+4,0,4);
+       memcpy(sa+6,&dest->sin.sin_port,2);
+       sendto(st->fd,sa,buf->size+8,0,(struct sockaddr *)&st->proxy,
+              sizeof(st->proxy));
+       buf_unprepend(buf,8);
+    } else {
+       sendto(st->fd, buf->start, buf->size, 0,
+              (struct sockaddr *)&dest->sin, sizeof(dest->sin));
+    }
 
     return True;
 }
 
+static void udp_phase_hook(void *sst, uint32_t new_phase)
+{
+    struct udp *st=sst;
+    struct sockaddr_in addr;
+
+    st->fd=socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
+    if (st->fd<0) {
+       fatal_perror("udp (%s:%d): socket",st->loc.file,st->loc.line);
+    }
+    if (fcntl(st->fd, F_SETFL, fcntl(st->fd, F_GETFL)|O_NONBLOCK)==-1) {
+       fatal_perror("udp (%s:%d): fcntl(set O_NONBLOCK)",
+                    st->loc.file,st->loc.line);
+    }
+    setcloexec(st->fd);
+
+    FILLZERO(addr);
+    addr.sin_family=AF_INET;
+    addr.sin_addr.s_addr=htonl(st->addr);
+    addr.sin_port=htons(st->port);
+    if (st->authbind) {
+       pid_t c;
+       int status;
+
+       /* XXX this fork() and waitpid() business needs to be hidden
+          in some system-specific library functions. */
+       c=fork();
+       if (c==-1) {
+           fatal_perror("udp_phase_hook: fork() for authbind");
+       }
+       if (c==0) {
+           char *argv[4], addrstr[9], portstr[5];
+           sprintf(addrstr,"%08lX",(long)addr.sin_addr.s_addr);
+           sprintf(portstr,"%04X",addr.sin_port);
+           argv[0]=st->authbind;
+           argv[1]=addrstr;
+           argv[2]=portstr;
+           argv[3]=NULL;
+           dup2(st->fd,0);
+           execvp(st->authbind,argv);
+           _exit(255);
+       }
+       while (waitpid(c,&status,0)==-1) {
+           if (errno==EINTR) continue;
+           fatal_perror("udp (%s:%d): authbind",st->loc.file,st->loc.line);
+       }
+       if (WIFSIGNALED(status)) {
+           fatal("udp (%s:%d): authbind died on signal %d",st->loc.file,
+                 st->loc.line, WTERMSIG(status));
+       }
+       if (WIFEXITED(status) && WEXITSTATUS(status)!=0) {
+           fatal("udp (%s:%d): authbind died with status %d",st->loc.file,
+                 st->loc.line, WEXITSTATUS(status));
+       }
+    } else {
+       if (bind(st->fd, (struct sockaddr *)&addr, sizeof(addr))!=0) {
+           fatal_perror("udp (%s:%d): bind",st->loc.file,st->loc.line);
+       }
+    }
+
+    register_for_poll(st,udp_beforepoll,udp_afterpoll,1,"udp");
+}
+
 static list_t *udp_apply(closure_t *self, struct cloc loc, dict_t *context,
                         list_t *args)
 {
     struct udp *st;
-    item_t *i;
+    item_t *i,*j;
     dict_t *d;
-    uint16_t local_port=0;
-    struct sockaddr_in addr;
+    list_t *l;
+    uint32_t a;
 
     st=safe_malloc(sizeof(*st),"udp_apply(st)");
     st->loc=loc;
@@ -164,6 +292,9 @@ static list_t *udp_apply(closure_t *self, struct cloc loc, dict_t *context,
     st->ops.request_notify=request_notify;
     st->ops.release_notify=release_notify;
     st->ops.sendmsg=udp_sendmsg;
+    st->ops.addr_to_string=addr_to_string;
+    st->port=0;
+    st->use_proxy=False;
 
     i=list_elem(args,0);
     if (!i || i->type!=t_dict) {
@@ -171,37 +302,36 @@ static list_t *udp_apply(closure_t *self, struct cloc loc, dict_t *context,
     }
     d=i->data.dict;
 
-    local_port=dict_read_number(d,"port",False,"udp",st->loc,0);
+    j=dict_find_item(d,"address",False,"udp",st->loc);
+    st->addr=j?string_item_to_ipaddr(j, "udp"):INADDR_ANY;
+    st->port=dict_read_number(d,"port",True,"udp",st->loc,0);
     st->rbuf=find_cl_if(d,"buffer",CL_BUFFER,True,"udp",st->loc);
-
-    st->fd=socket(AF_INET, SOCK_DGRAM, 0);
-    if (st->fd<0) {
-       fatal_perror("udp_apply (%s:%d): socket",loc.file,loc.line);
-    }
-    if (fcntl(st->fd, F_SETFL, fcntl(st->fd, F_GETFL)|O_NONBLOCK)==-1) {
-       fatal_perror("udp_apply (%s:%d): fcntl(set O_NONBLOCK)",
-                    loc.file,loc.line);
-    }
-    if (fcntl(st->fd, F_SETFD, FD_CLOEXEC)==-1) {
-       fatal_perror("udp_apply (%s:%d): fcntl(set FD_CLOEXEC)",
-                    loc.file,loc.line);
+    st->authbind=dict_read_string(d,"authbind",False,"udp",st->loc);
+    l=dict_lookup(d,"proxy");
+    if (l) {
+       st->use_proxy=True;
+       FILLZERO(st->proxy);
+       st->proxy.sin_family=AF_INET;
+       i=list_elem(l,0);
+       if (!i || i->type!=t_string) {
+           cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
+       }
+       a=string_item_to_ipaddr(i,"proxy");
+       st->proxy.sin_addr.s_addr=htonl(a);
+       i=list_elem(l,1);
+       if (!i || i->type!=t_number) {
+           cfgfatal(st->loc,"udp","proxy must supply ""addr"",port\n");
+       }
+       st->proxy.sin_port=htons(i->data.number);
     }
 
-    memset(&addr, 0, sizeof(addr));
-    addr.sin_family=AF_INET;
-    if (local_port) {
-       addr.sin_port=htons(local_port);
-    }
-    if (bind(st->fd, (struct sockaddr *)&addr, sizeof(addr))!=0) {
-       fatal_perror("udp_apply (%s:%d): bind",loc.file,loc.line);
-    }
+    update_max_start_pad(&comm_max_start_pad, st->use_proxy ? 8 : 0);
 
-    register_for_poll(st,udp_beforepoll,udp_afterpoll,1,"udp");
+    add_hook(PHASE_GETRESOURCES,udp_phase_hook,st);
 
     return new_closure(&st->cl);
 }
 
-init_module udp_module;
 void udp_module(dict_t *dict)
 {
     add_closure(dict,"udp",udp_apply);