src/process/posix_spawn.c

   1 #define _GNU_SOURCE
   2 #include <spawn.h>
   3 #include <sched.h>
   4 #include <unistd.h>
   5 #include <signal.h>
   6 #include <fcntl.h>
   7 #include <sys/wait.h>
   8 #include "syscall.h"
   9 #include "pthread_impl.h"
  10 #include "fdop.h"
  11
  12 struct args {
  13         int p[2];
  14         sigset_t oldmask;
  15         const char *path;
  16         const posix_spawn_file_actions_t *fa;
  17         const posix_spawnattr_t *restrict attr;
  18         char *const *argv, *const *envp;
  19 };
  20
  21 static int __sys_dup2(int old, int new)
  22 {
  23 #ifdef SYS_dup2
  24         return __syscall(SYS_dup2, old, new);
  25 #else
  26         return __syscall(SYS_dup3, old, new, 0);
  27 #endif
  28 }
  29
  30 static int child(void *args_vp)
  31 {
  32         int i, ret;
  33         struct sigaction sa = {0};
  34         struct args *args = args_vp;
  35         int p = args->p[1];
  36         const posix_spawn_file_actions_t *fa = args->fa;
  37         const posix_spawnattr_t *restrict attr = args->attr;
  38         sigset_t hset;
  39
  40         close(args->p[0]);
  41
  42         /* All signal dispositions must be either SIG_DFL or SIG_IGN
  43          * before signals are unblocked. Otherwise a signal handler
  44          * from the parent might get run in the child while sharing
  45          * memory, with unpredictable and dangerous results. To
  46          * reduce overhead, sigaction has tracked for us which signals
  47          * potentially have a signal handler. */
  48         __get_handler_set(&hset);
  49         for (i=1; i<_NSIG; i++) {
  50                 if ((attr->__flags & POSIX_SPAWN_SETSIGDEF)
  51                      && sigismember(&attr->__def, i)) {
  52                         sa.sa_handler = SIG_DFL;
  53                 } else if (sigismember(&hset, i)) {
  54                         if (i-32<3U) {
  55                                 sa.sa_handler = SIG_IGN;
  56                         } else {
  57                                 __libc_sigaction(i, 0, &sa);
  58                                 if (sa.sa_handler==SIG_IGN) continue;
  59                                 sa.sa_handler = SIG_DFL;
  60                         }
  61                 } else {
  62                         continue;
  63                 }
  64                 __libc_sigaction(i, &sa, 0);
  65         }
  66
  67         if (attr->__flags & POSIX_SPAWN_SETSID)
  68                 if ((ret=__syscall(SYS_setsid)) < 0)
  69                         goto fail;
  70
  71         if (attr->__flags & POSIX_SPAWN_SETPGROUP)
  72                 if ((ret=__syscall(SYS_setpgid, 0, attr->__pgrp)))
  73                         goto fail;
  74
  75         /* Use syscalls directly because the library functions attempt
  76          * to do a multi-threaded synchronized id-change, which would
  77          * trash the parent's state. */
  78         if (attr->__flags & POSIX_SPAWN_RESETIDS)
  79                 if ((ret=__syscall(SYS_setgid, __syscall(SYS_getgid))) ||
  80                     (ret=__syscall(SYS_setuid, __syscall(SYS_getuid))) )
  81                         goto fail;
  82
  83         if (fa && fa->__actions) {
  84                 struct fdop *op;
  85                 int fd;
  86                 for (op = fa->__actions; op->next; op = op->next);
  87                 for (; op; op = op->prev) {
  88                         /* It's possible that a file operation would clobber
  89                          * the pipe fd used for synchronizing with the
  90                          * parent. To avoid that, we dup the pipe onto
  91                          * an unoccupied fd. */
  92                         if (op->fd == p) {
  93                                 ret = __syscall(SYS_dup, p);
  94                                 if (ret < 0) goto fail;
  95                                 __syscall(SYS_close, p);
  96                                 p = ret;
  97                         }
  98                         switch(op->cmd) {
  99                         case FDOP_CLOSE:
 100                                 __syscall(SYS_close, op->fd);
 101                                 break;
 102                         case FDOP_DUP2:
 103                                 fd = op->srcfd;
 104                                 if (fd != op->fd) {
 105                                         if ((ret=__sys_dup2(fd, op->fd))<0)
 106                                                 goto fail;
 107                                 } else {
 108                                         ret = __syscall(SYS_fcntl, fd, F_GETFD);
 109                                         ret = __syscall(SYS_fcntl, fd, F_SETFD,
 110                                                         ret & ~FD_CLOEXEC);
 111                                         if (ret<0)
 112                                                 goto fail;
 113                                 }
 114                                 break;
 115                         case FDOP_OPEN:
 116                                 fd = __sys_open(op->path, op->oflag, op->mode);
 117                                 if ((ret=fd) < 0) goto fail;
 118                                 if (fd != op->fd) {
 119                                         if ((ret=__sys_dup2(fd, op->fd))<0)
 120                                                 goto fail;
 121                                         __syscall(SYS_close, fd);
 122                                 }
 123                                 break;
 124                         }
 125                 }
 126         }
 127
 128         /* Close-on-exec flag may have been lost if we moved the pipe
 129          * to a different fd. We don't use F_DUPFD_CLOEXEC above because
 130          * it would fail on older kernels and atomicity is not needed --
 131          * in this process there are no threads or signal handlers. */
 132         __syscall(SYS_fcntl, p, F_SETFD, FD_CLOEXEC);
 133
 134         pthread_sigmask(SIG_SETMASK, (attr->__flags & POSIX_SPAWN_SETSIGMASK)
 135                 ? &attr->__mask : &args->oldmask, 0);
 136
 137         int (*exec)(const char *, char *const *, char *const *) =
 138                 attr->__fn ? (int (*)())attr->__fn : execve;
 139
 140         exec(args->path, args->argv, args->envp);
 141         ret = -errno;
 142
 143 fail:
 144         /* Since sizeof errno < PIPE_BUF, the write is atomic. */
 145         ret = -ret;
 146         if (ret) while (__syscall(SYS_write, p, &ret, sizeof ret) < 0);
 147         _exit(127);
 148 }
 149
 150
 151 int posix_spawn(pid_t *restrict res, const char *restrict path,
 152         const posix_spawn_file_actions_t *fa,
 153         const posix_spawnattr_t *restrict attr,
 154         char *const argv[restrict], char *const envp[restrict])
 155 {
 156         pid_t pid;
 157         char stack[1024+PATH_MAX];
 158         int ec=0, cs;
 159         struct args args;
 160
 161         if (pipe2(args.p, O_CLOEXEC))
 162                 return errno;
 163
 164         pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
 165
 166         args.path = path;
 167         args.fa = fa;
 168         args.attr = attr ? attr : &(const posix_spawnattr_t){0};
 169         args.argv = argv;
 170         args.envp = envp;
 171         pthread_sigmask(SIG_BLOCK, SIGALL_SET, &args.oldmask);
 172
 173         pid = __clone(child, stack+sizeof stack,
 174                 CLONE_VM|CLONE_VFORK|SIGCHLD, &args);
 175         close(args.p[1]);
 176
 177         if (pid > 0) {
 178                 if (read(args.p[0], &ec, sizeof ec) != sizeof ec) ec = 0;
 179                 else waitpid(pid, &(int){0}, 0);
 180         } else {
 181                 ec = -pid;
 182         }
 183
 184         close(args.p[0]);
 185
 186         if (!ec && res) *res = pid;
 187
 188         pthread_sigmask(SIG_SETMASK, &args.oldmask, 0);
 189         pthread_setcancelstate(cs, 0);
 190
 191         return ec;
 192 }