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
__sys_dup2(int old,int new)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
child(void * args_vp)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 == p) {
105 ret = -EBADF;
106 goto fail;
107 }
108 if (fd != op->fd) {
109 if ((ret=__sys_dup2(fd, op->fd))<0)
110 goto fail;
111 } else {
112 ret = __syscall(SYS_fcntl, fd, F_GETFD);
113 ret = __syscall(SYS_fcntl, fd, F_SETFD,
114 ret & ~FD_CLOEXEC);
115 if (ret<0)
116 goto fail;
117 }
118 break;
119 case FDOP_OPEN:
120 fd = __sys_open(op->path, op->oflag, op->mode);
121 if ((ret=fd) < 0) goto fail;
122 if (fd != op->fd) {
123 if ((ret=__sys_dup2(fd, op->fd))<0)
124 goto fail;
125 __syscall(SYS_close, fd);
126 }
127 break;
128 case FDOP_CHDIR:
129 ret = __syscall(SYS_chdir, op->path);
130 if (ret<0) goto fail;
131 break;
132 case FDOP_FCHDIR:
133 ret = __syscall(SYS_fchdir, op->fd);
134 if (ret<0) goto fail;
135 break;
136 }
137 }
138 }
139
140 /* Close-on-exec flag may have been lost if we moved the pipe
141 * to a different fd. We don't use F_DUPFD_CLOEXEC above because
142 * it would fail on older kernels and atomicity is not needed --
143 * in this process there are no threads or signal handlers. */
144 __syscall(SYS_fcntl, p, F_SETFD, FD_CLOEXEC);
145
146 pthread_sigmask(SIG_SETMASK, (attr->__flags & POSIX_SPAWN_SETSIGMASK)
147 ? &attr->__mask : &args->oldmask, 0);
148
149 int (*exec)(const char *, char *const *, char *const *) =
150 attr->__fn ? (int (*)())attr->__fn : execve;
151
152 exec(args->path, args->argv, args->envp);
153 ret = -errno;
154
155 fail:
156 /* Since sizeof errno < PIPE_BUF, the write is atomic. */
157 ret = -ret;
158 if (ret) while (__syscall(SYS_write, p, &ret, sizeof ret) < 0);
159 _exit(127);
160 }
161
162
posix_spawn(pid_t * restrict res,const char * restrict path,const posix_spawn_file_actions_t * fa,const posix_spawnattr_t * restrict attr,char * const argv[restrict],char * const envp[restrict])163 int posix_spawn(pid_t *restrict res, const char *restrict path,
164 const posix_spawn_file_actions_t *fa,
165 const posix_spawnattr_t *restrict attr,
166 char *const argv[restrict], char *const envp[restrict])
167 {
168 pid_t pid;
169 char stack[1024+PATH_MAX];
170 int ec=0, cs;
171 struct args args;
172
173 if (pipe2(args.p, O_CLOEXEC))
174 return errno;
175
176 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
177
178 args.path = path;
179 args.fa = fa;
180 args.attr = attr ? attr : &(const posix_spawnattr_t){0};
181 args.argv = argv;
182 args.envp = envp;
183 pthread_sigmask(SIG_BLOCK, SIGALL_SET, &args.oldmask);
184
185 pid = __clone(child, stack+sizeof stack,
186 CLONE_VM|CLONE_VFORK|SIGCHLD, &args);
187 close(args.p[1]);
188
189 if (pid > 0) {
190 if (read(args.p[0], &ec, sizeof ec) != sizeof ec) ec = 0;
191 else waitpid(pid, &(int){0}, 0);
192 } else {
193 ec = -pid;
194 }
195
196 close(args.p[0]);
197
198 if (!ec && res) *res = pid;
199
200 pthread_sigmask(SIG_SETMASK, &args.oldmask, 0);
201 pthread_setcancelstate(cs, 0);
202
203 return ec;
204 }
205