posix_spawn.c raw
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 "lock.h"
10 #include "pthread_impl.h"
11 #include "fdop.h"
12
13 struct args {
14 int p[2];
15 sigset_t oldmask;
16 const char *path;
17 const posix_spawn_file_actions_t *fa;
18 const posix_spawnattr_t *restrict attr;
19 char *const *argv, *const *envp;
20 };
21
22 static int __sys_dup2(int old, int new)
23 {
24 #ifdef SYS_dup2
25 return __syscall(SYS_dup2, old, new);
26 #else
27 return __syscall(SYS_dup3, old, new, 0);
28 #endif
29 }
30
31 static int child(void *args_vp)
32 {
33 int i, ret;
34 struct sigaction sa = {0};
35 struct args *args = args_vp;
36 int p = args->p[1];
37 const posix_spawn_file_actions_t *fa = args->fa;
38 const posix_spawnattr_t *restrict attr = args->attr;
39 sigset_t hset;
40
41 close(args->p[0]);
42
43 /* All signal dispositions must be either SIG_DFL or SIG_IGN
44 * before signals are unblocked. Otherwise a signal handler
45 * from the parent might get run in the child while sharing
46 * memory, with unpredictable and dangerous results. To
47 * reduce overhead, sigaction has tracked for us which signals
48 * potentially have a signal handler. */
49 __get_handler_set(&hset);
50 for (i=1; i<_NSIG; i++) {
51 if ((attr->__flags & POSIX_SPAWN_SETSIGDEF)
52 && sigismember(&attr->__def, i)) {
53 sa.sa_handler = SIG_DFL;
54 } else if (sigismember(&hset, i)) {
55 if (i-32<3U) {
56 sa.sa_handler = SIG_IGN;
57 } else {
58 __libc_sigaction(i, 0, &sa);
59 if (sa.sa_handler==SIG_IGN) continue;
60 sa.sa_handler = SIG_DFL;
61 }
62 } else {
63 continue;
64 }
65 __libc_sigaction(i, &sa, 0);
66 }
67
68 if (attr->__flags & POSIX_SPAWN_SETSID)
69 if ((ret=__syscall(SYS_setsid)) < 0)
70 goto fail;
71
72 if (attr->__flags & POSIX_SPAWN_SETPGROUP)
73 if ((ret=__syscall(SYS_setpgid, 0, attr->__pgrp)))
74 goto fail;
75
76 /* Use syscalls directly because the library functions attempt
77 * to do a multi-threaded synchronized id-change, which would
78 * trash the parent's state. */
79 if (attr->__flags & POSIX_SPAWN_RESETIDS)
80 if ((ret=__syscall(SYS_setgid, __syscall(SYS_getgid))) ||
81 (ret=__syscall(SYS_setuid, __syscall(SYS_getuid))) )
82 goto fail;
83
84 if (fa && fa->__actions) {
85 struct fdop *op;
86 int fd;
87 for (op = fa->__actions; op->next; op = op->next);
88 for (; op; op = op->prev) {
89 /* It's possible that a file operation would clobber
90 * the pipe fd used for synchronizing with the
91 * parent. To avoid that, we dup the pipe onto
92 * an unoccupied fd. */
93 if (op->fd == p) {
94 ret = __syscall(SYS_dup, p);
95 if (ret < 0) goto fail;
96 __syscall(SYS_close, p);
97 p = ret;
98 }
99 switch(op->cmd) {
100 case FDOP_CLOSE:
101 __syscall(SYS_close, op->fd);
102 break;
103 case FDOP_DUP2:
104 fd = op->srcfd;
105 if (fd == p) {
106 ret = -EBADF;
107 goto fail;
108 }
109 if (fd != op->fd) {
110 if ((ret=__sys_dup2(fd, op->fd))<0)
111 goto fail;
112 } else {
113 ret = __syscall(SYS_fcntl, fd, F_GETFD);
114 ret = __syscall(SYS_fcntl, fd, F_SETFD,
115 ret & ~FD_CLOEXEC);
116 if (ret<0)
117 goto fail;
118 }
119 break;
120 case FDOP_OPEN:
121 fd = __sys_open(op->path, op->oflag, op->mode);
122 if ((ret=fd) < 0) goto fail;
123 if (fd != op->fd) {
124 if ((ret=__sys_dup2(fd, op->fd))<0)
125 goto fail;
126 __syscall(SYS_close, fd);
127 }
128 break;
129 case FDOP_CHDIR:
130 ret = __syscall(SYS_chdir, op->path);
131 if (ret<0) goto fail;
132 break;
133 case FDOP_FCHDIR:
134 ret = __syscall(SYS_fchdir, op->fd);
135 if (ret<0) goto fail;
136 break;
137 }
138 }
139 }
140
141 /* Close-on-exec flag may have been lost if we moved the pipe
142 * to a different fd. We don't use F_DUPFD_CLOEXEC above because
143 * it would fail on older kernels and atomicity is not needed --
144 * in this process there are no threads or signal handlers. */
145 __syscall(SYS_fcntl, p, F_SETFD, FD_CLOEXEC);
146
147 pthread_sigmask(SIG_SETMASK, (attr->__flags & POSIX_SPAWN_SETSIGMASK)
148 ? &attr->__mask : &args->oldmask, 0);
149
150 int (*exec)(const char *, char *const *, char *const *) =
151 attr->__fn ? (int (*)())attr->__fn : execve;
152
153 exec(args->path, args->argv, args->envp);
154 ret = -errno;
155
156 fail:
157 /* Since sizeof errno < PIPE_BUF, the write is atomic. */
158 ret = -ret;
159 if (ret) while (__syscall(SYS_write, p, &ret, sizeof ret) < 0);
160 _exit(127);
161 }
162
163
164 int posix_spawn(pid_t *restrict res, const char *restrict path,
165 const posix_spawn_file_actions_t *fa,
166 const posix_spawnattr_t *restrict attr,
167 char *const argv[restrict], char *const envp[restrict])
168 {
169 pid_t pid;
170 char stack[1024+PATH_MAX];
171 int ec=0, cs;
172 struct args args;
173
174 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
175
176 args.path = path;
177 args.fa = fa;
178 args.attr = attr ? attr : &(const posix_spawnattr_t){0};
179 args.argv = argv;
180 args.envp = envp;
181 pthread_sigmask(SIG_BLOCK, SIGALL_SET, &args.oldmask);
182
183 /* The lock guards both against seeing a SIGABRT disposition change
184 * by abort and against leaking the pipe fd to fork-without-exec. */
185 LOCK(__abort_lock);
186
187 if (pipe2(args.p, O_CLOEXEC)) {
188 UNLOCK(__abort_lock);
189 ec = errno;
190 goto fail;
191 }
192
193 pid = __clone(child, stack+sizeof stack,
194 CLONE_VM|CLONE_VFORK|SIGCHLD, &args);
195 close(args.p[1]);
196 UNLOCK(__abort_lock);
197
198 if (pid > 0) {
199 if (read(args.p[0], &ec, sizeof ec) != sizeof ec) ec = 0;
200 else waitpid(pid, &(int){0}, 0);
201 } else {
202 ec = -pid;
203 }
204
205 close(args.p[0]);
206
207 if (!ec && res) *res = pid;
208
209 fail:
210 pthread_sigmask(SIG_SETMASK, &args.oldmask, 0);
211 pthread_setcancelstate(cs, 0);
212
213 return ec;
214 }
215