daemon.c

   1 #include "cache.h"
   2 #include "pkt-line.h"
   3 #include <signal.h>
   4 #include <sys/wait.h>
   5 #include <sys/socket.h>
   6 #include <netdb.h>
   7 #include <netinet/in.h>
   8
   9 static const char daemon_usage[] = "git-daemon [--inetd | --port=n]";
  10
  11 static int upload(char *dir, int dirlen)
  12 {
  13         if (chdir(dir) < 0)
  14                 return -1;
  15         chdir(".git");
  16
  17         /*
  18          * Security on the cheap.
  19          *
  20          * We want a readable HEAD, usable "objects" directory, and
  21          * a "git-daemon-export-ok" flag that says that the other side
  22          * is ok with us doing this.
  23          */
  24         if (access("git-daemon-export-ok", F_OK) ||
  25             access("objects/00", X_OK) ||
  26             access("HEAD", R_OK))
  27                 return -1;
  28
  29         /*
  30          * We'll ignore SIGTERM from now on, we have a
  31          * good client.
  32          */
  33         signal(SIGTERM, SIG_IGN);
  34
  35         /* git-upload-pack only ever reads stuff, so this is safe */
  36         execlp("git-upload-pack", "git-upload-pack", ".", NULL);
  37         return -1;
  38 }
  39
  40 static int execute(void)
  41 {
  42         static char line[1000];
  43         int len;
  44
  45         len = packet_read_line(0, line, sizeof(line));
  46
  47         if (len && line[len-1] == '\n')
  48                 line[--len] = 0;
  49
  50         if (!strncmp("git-upload-pack /", line, 17))
  51                 return upload(line + 16, len - 16);
  52
  53         fprintf(stderr, "got bad connection '%s'\n", line);
  54         return -1;
  55 }
  56
  57
  58 /*
  59  * We count spawned/reaped separately, just to avoid any
  60  * races when updating them from signals. The SIGCHLD handler
  61  * will only update children_reaped, and the fork logic will
  62  * only update children_spawned.
  63  *
  64  * MAX_CHILDREN should be a power-of-two to make the modulus
  65  * operation cheap. It should also be at least twice
  66  * the maximum number of connections we will ever allow.
  67  */
  68 #define MAX_CHILDREN 128
  69
  70 static int max_connections = 25;
  71
  72 /* These are updated by the signal handler */
  73 static volatile unsigned int children_reaped = 0;
  74 pid_t dead_child[MAX_CHILDREN];
  75
  76 /* These are updated by the main loop */
  77 static unsigned int children_spawned = 0;
  78 static unsigned int children_deleted = 0;
  79
  80 struct child {
  81         pid_t pid;
  82         socklen_t addrlen;
  83         struct sockaddr_storage address;
  84 } live_child[MAX_CHILDREN];
  85
  86 static void add_child(int idx, pid_t pid, struct sockaddr *addr, socklen_t addrlen)
  87 {
  88         live_child[idx].pid = pid;
  89         live_child[idx].addrlen = addrlen;
  90         memcpy(&live_child[idx].address, addr, addrlen);
  91 }
  92
  93 /*
  94  * Walk from "deleted" to "spawned", and remove child "pid".
  95  *
  96  * We move everything up by one, since the new "deleted" will
  97  * be one higher.
  98  */
  99 static void remove_child(pid_t pid, unsigned deleted, unsigned spawned)
 100 {
 101         struct child n;
 102
 103         deleted %= MAX_CHILDREN;
 104         spawned %= MAX_CHILDREN;
 105         if (live_child[deleted].pid == pid) {
 106                 live_child[deleted].pid = -1;
 107                 return;
 108         }
 109         n = live_child[deleted];
 110         for (;;) {
 111                 struct child m;
 112                 deleted = (deleted + 1) % MAX_CHILDREN;
 113                 if (deleted == spawned)
 114                         die("could not find dead child %d\n", pid);
 115                 m = live_child[deleted];
 116                 live_child[deleted] = n;
 117                 if (m.pid == pid)
 118                         return;
 119                 n = m;
 120         }
 121 }
 122
 123 /*
 124  * This gets called if the number of connections grows
 125  * past "max_connections".
 126  *
 127  * We _should_ start off by searching for connections
 128  * from the same IP, and if there is some address wth
 129  * multiple connections, we should kill that first.
 130  *
 131  * As it is, we just "randomly" kill 25% of the connections,
 132  * and our pseudo-random generator sucks too. I have no
 133  * shame.
 134  *
 135  * Really, this is just a place-holder for a _real_ algorithm.
 136  */
 137 static void kill_some_children(int signo, unsigned start, unsigned stop)
 138 {
 139         start %= MAX_CHILDREN;
 140         stop %= MAX_CHILDREN;
 141         while (start != stop) {
 142                 if (!(start & 3))
 143                         kill(live_child[start].pid, signo);
 144                 start = (start + 1) % MAX_CHILDREN;
 145         }
 146 }
 147
 148 static void check_max_connections(void)
 149 {
 150         for (;;) {
 151                 int active;
 152                 unsigned spawned, reaped, deleted;
 153
 154                 spawned = children_spawned;
 155                 reaped = children_reaped;
 156                 deleted = children_deleted;
 157
 158                 while (deleted < reaped) {
 159                         pid_t pid = dead_child[deleted % MAX_CHILDREN];
 160                         remove_child(pid, deleted, spawned);
 161                         deleted++;
 162                 }
 163                 children_deleted = deleted;
 164
 165                 active = spawned - deleted;
 166                 if (active <= max_connections)
 167                         break;
 168
 169                 /* Kill some unstarted connections with SIGTERM */
 170                 kill_some_children(SIGTERM, deleted, spawned);
 171                 if (active <= max_connections << 1)
 172                         break;
 173
 174                 /* If the SIGTERM thing isn't helping use SIGKILL */
 175                 kill_some_children(SIGKILL, deleted, spawned);
 176                 sleep(1);
 177         }
 178 }
 179
 180 static void handle(int incoming, struct sockaddr *addr, socklen_t addrlen)
 181 {
 182         pid_t pid = fork();
 183
 184         if (pid) {
 185                 unsigned idx;
 186
 187                 close(incoming);
 188                 if (pid < 0)
 189                         return;
 190
 191                 idx = children_spawned % MAX_CHILDREN;
 192                 children_spawned++;
 193                 add_child(idx, pid, addr, addrlen);
 194
 195                 check_max_connections();
 196                 return;
 197         }
 198
 199         dup2(incoming, 0);
 200         dup2(incoming, 1);
 201         close(incoming);
 202         exit(execute());
 203 }
 204
 205 static void child_handler(int signo)
 206 {
 207         for (;;) {
 208                 pid_t pid = waitpid(-1, NULL, WNOHANG);
 209
 210                 if (pid > 0) {
 211                         unsigned reaped = children_reaped;
 212                         dead_child[reaped % MAX_CHILDREN] = pid;
 213                         children_reaped = reaped + 1;
 214                         continue;
 215                 }
 216                 break;
 217         }
 218 }
 219
 220 static int serve(int port)
 221 {
 222         struct addrinfo hints, *ai0, *ai;
 223         int gai;
 224         int socknum = 0, *socklist = NULL;
 225         int maxfd = -1;
 226         fd_set fds_init, fds;
 227         char pbuf[NI_MAXSERV];
 228
 229         signal(SIGCHLD, child_handler);
 230
 231         sprintf(pbuf, "%d", port);
 232         memset(&hints, 0, sizeof(hints));
 233         hints.ai_family = AF_UNSPEC;
 234         hints.ai_socktype = SOCK_STREAM;
 235         hints.ai_protocol = IPPROTO_TCP;
 236         hints.ai_flags = AI_PASSIVE;
 237
 238         gai = getaddrinfo(NULL, pbuf, &hints, &ai0);
 239         if (gai)
 240                 die("getaddrinfo() failed: %s\n", gai_strerror(gai));
 241
 242         FD_ZERO(&fds_init);
 243
 244         for (ai = ai0; ai; ai = ai->ai_next) {
 245                 int sockfd;
 246                 int *newlist;
 247
 248                 sockfd = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
 249                 if (sockfd < 0)
 250                         continue;
 251                 if (sockfd >= FD_SETSIZE) {
 252                         error("too large socket descriptor.");
 253                         close(sockfd);
 254                         continue;
 255                 }
 256
 257 #ifdef IPV6_V6ONLY
 258                 if (ai->ai_family == AF_INET6) {
 259                         int on = 1;
 260                         setsockopt(sockfd, IPPROTO_IPV6, IPV6_V6ONLY,
 261                                    &on, sizeof(on));
 262                         /* Note: error is not fatal */
 263                 }
 264 #endif
 265
 266                 if (bind(sockfd, ai->ai_addr, ai->ai_addrlen) < 0) {
 267                         close(sockfd);
 268                         continue;       /* not fatal */
 269                 }
 270                 if (listen(sockfd, 5) < 0) {
 271                         close(sockfd);
 272                         continue;       /* not fatal */
 273                 }
 274
 275                 newlist = realloc(socklist, sizeof(int) * (socknum + 1));
 276                 if (!newlist)
 277                         die("memory allocation failed: %s", strerror(errno));
 278
 279                 socklist = newlist;
 280                 socklist[socknum++] = sockfd;
 281
 282                 FD_SET(sockfd, &fds_init);
 283                 if (maxfd < sockfd)
 284                         maxfd = sockfd;
 285         }
 286
 287         freeaddrinfo(ai0);
 288
 289         if (socknum == 0)
 290                 die("unable to allocate any listen sockets on port %u", port);
 291
 292         for (;;) {
 293                 int i;
 294                 fds = fds_init;
 295
 296                 if (select(maxfd + 1, &fds, NULL, NULL, NULL) < 0) {
 297                         error("select failed, resuming: %s", strerror(errno));
 298                         sleep(1);
 299                         continue;
 300                 }
 301
 302                 for (i = 0; i < socknum; i++) {
 303                         int sockfd = socklist[i];
 304
 305                         if (FD_ISSET(sockfd, &fds)) {
 306                                 struct sockaddr_storage ss;
 307                                 socklen_t sslen = sizeof(ss);
 308                                 int incoming = accept(sockfd, (struct sockaddr *)&ss, &sslen);
 309                                 if (incoming < 0) {
 310                                         switch (errno) {
 311                                         case EAGAIN:
 312                                         case EINTR:
 313                                         case ECONNABORTED:
 314                                                 continue;
 315                                         default:
 316                                                 die("accept returned %s", strerror(errno));
 317                                         }
 318                                 }
 319                                 handle(incoming, (struct sockaddr *)&ss, sslen);
 320                         }
 321                 }
 322         }
 323 }
 324
 325 int main(int argc, char **argv)
 326 {
 327         int port = DEFAULT_GIT_PORT;
 328         int inetd_mode = 0;
 329         int i;
 330
 331         for (i = 1; i < argc; i++) {
 332                 char *arg = argv[i];
 333
 334                 if (!strncmp(arg, "--port=", 7)) {
 335                         char *end;
 336                         unsigned long n;
 337                         n = strtoul(arg+7, &end, 0);
 338                         if (arg[7] && !*end) {
 339                                 port = n;
 340                                 continue;
 341                         }
 342                 }
 343
 344                 if (!strcmp(arg, "--inetd")) {
 345                         inetd_mode = 1;
 346                         continue;
 347                 }
 348
 349                 usage(daemon_usage);
 350         }
 351
 352         if (inetd_mode)
 353                 return execute();
 354
 355         return serve(port);
 356 }