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 <netinet/in.h>
   7 #include <arpa/inet.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         int addrlen;
  83         struct sockaddr_in address;
  84 } live_child[MAX_CHILDREN];
  85
  86 static void add_child(int idx, pid_t pid, struct sockaddr_in *addr, int addrlen)
  87 {
  88         live_child[idx].pid = pid;
  89         live_child[idx].addrlen = addrlen;
  90         live_child[idx].address = *addr;
  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_in *addr, int 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         int sockfd;
 223         struct sockaddr_in addr;
 224
 225         signal(SIGCHLD, child_handler);
 226         sockfd = socket(PF_INET, SOCK_STREAM, IPPROTO_IP);
 227         if (sockfd < 0)
 228                 die("unable to open socket (%s)", strerror(errno));
 229         memset(&addr, 0, sizeof(addr));
 230         addr.sin_port = htons(port);
 231         addr.sin_family = AF_INET;
 232         if (bind(sockfd, (void *)&addr, sizeof(addr)) < 0)
 233                 die("unable to bind to port %d (%s)", port, strerror(errno));
 234         if (listen(sockfd, 5) < 0)
 235                 die("unable to listen to port %d (%s)", port, strerror(errno));
 236
 237         for (;;) {
 238                 struct sockaddr_in in;
 239                 socklen_t addrlen = sizeof(in);
 240                 int incoming = accept(sockfd, (void *)&in, &addrlen);
 241
 242                 if (incoming < 0) {
 243                         switch (errno) {
 244                         case EAGAIN:
 245                         case EINTR:
 246                         case ECONNABORTED:
 247                                 continue;
 248                         default:
 249                                 die("accept returned %s", strerror(errno));
 250                         }
 251                 }
 252                 handle(incoming, &in, addrlen);
 253         }
 254 }
 255
 256 int main(int argc, char **argv)
 257 {
 258         int port = DEFAULT_GIT_PORT;
 259         int inetd_mode = 0;
 260         int i;
 261
 262         for (i = 1; i < argc; i++) {
 263                 char *arg = argv[i];
 264
 265                 if (!strncmp(arg, "--port=", 7)) {
 266                         char *end;
 267                         unsigned long n;
 268                         n = strtoul(arg+7, &end, 0);
 269                         if (arg[7] && !*end) {
 270                                 port = n;
 271                                 continue;
 272                         }
 273                 }
 274
 275                 if (!strcmp(arg, "--inetd")) {
 276                         inetd_mode = 1;
 277                         continue;
 278                 }
 279
 280                 usage(daemon_usage);
 281         }
 282
 283         if (inetd_mode)
 284                 return execute();
 285
 286         return serve(port);
 287 }