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/****************************************************************************
* bfs *
* Copyright (C) 2018-2019 Tavian Barnes <tavianator@tavianator.com> *
* *
* Permission to use, copy, modify, and/or distribute this software for any *
* purpose with or without fee is hereby granted. *
* *
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES *
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF *
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR *
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES *
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN *
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF *
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. *
****************************************************************************/
#include "spawn.h"
#include "util.h"
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
/**
* Types of spawn actions.
*/
enum bfs_spawn_op {
BFS_SPAWN_CLOSE,
BFS_SPAWN_DUP2,
BFS_SPAWN_FCHDIR,
};
/**
* A spawn action.
*/
struct bfs_spawn_action {
struct bfs_spawn_action *next;
enum bfs_spawn_op op;
int in_fd;
int out_fd;
};
int bfs_spawn_init(struct bfs_spawn *ctx) {
ctx->flags = 0;
ctx->actions = NULL;
ctx->tail = &ctx->actions;
return 0;
}
int bfs_spawn_destroy(struct bfs_spawn *ctx) {
struct bfs_spawn_action *action = ctx->actions;
while (action) {
struct bfs_spawn_action *next = action->next;
free(action);
action = next;
}
return 0;
}
int bfs_spawn_setflags(struct bfs_spawn *ctx, enum bfs_spawn_flags flags) {
ctx->flags = flags;
return 0;
}
/** Add a spawn action to the chain. */
static struct bfs_spawn_action *bfs_spawn_add(struct bfs_spawn *ctx, enum bfs_spawn_op op) {
struct bfs_spawn_action *action = malloc(sizeof(*action));
if (action) {
action->next = NULL;
action->op = op;
action->in_fd = -1;
action->out_fd = -1;
*ctx->tail = action;
ctx->tail = &action->next;
}
return action;
}
int bfs_spawn_addclose(struct bfs_spawn *ctx, int fd) {
if (fd < 0) {
errno = EBADF;
return -1;
}
struct bfs_spawn_action *action = bfs_spawn_add(ctx, BFS_SPAWN_CLOSE);
if (action) {
action->out_fd = fd;
return 0;
} else {
return -1;
}
}
int bfs_spawn_adddup2(struct bfs_spawn *ctx, int oldfd, int newfd) {
if (oldfd < 0 || newfd < 0) {
errno = EBADF;
return -1;
}
struct bfs_spawn_action *action = bfs_spawn_add(ctx, BFS_SPAWN_DUP2);
if (action) {
action->in_fd = oldfd;
action->out_fd = newfd;
return 0;
} else {
return -1;
}
}
int bfs_spawn_addfchdir(struct bfs_spawn *ctx, int fd) {
if (fd < 0) {
errno = EBADF;
return -1;
}
struct bfs_spawn_action *action = bfs_spawn_add(ctx, BFS_SPAWN_FCHDIR);
if (action) {
action->in_fd = fd;
return 0;
} else {
return -1;
}
}
/** Facade for execvpe() which is non-standard. */
static int bfs_execvpe(const char *exe, char **argv, char **envp) {
#if __GLIBC__ || __linux__ || __NetBSD__ || __OpenBSD__
return execvpe(exe, argv, envp);
#else
extern char **environ;
environ = envp;
return execvp(exe, argv);
#endif
}
/** Actually exec() the new process. */
static void bfs_spawn_exec(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp, int pipefd[2]) {
int error;
enum bfs_spawn_flags flags = ctx ? ctx->flags : 0;
const struct bfs_spawn_action *actions = ctx ? ctx->actions : NULL;
close(pipefd[0]);
for (const struct bfs_spawn_action *action = actions; action; action = action->next) {
// Pretend the error-reporting pipe doesn't exist
if (action->in_fd == pipefd[1]) {
errno = EBADF;
goto fail;
}
// Move the pipe out of the way if necessary
if (action->out_fd == pipefd[1]) {
int fd = dup_cloexec(pipefd[1]);
if (fd < 0) {
goto fail;
}
close(pipefd[1]);
pipefd[1] = fd;
}
switch (action->op) {
case BFS_SPAWN_CLOSE:
if (close(action->out_fd) != 0) {
goto fail;
}
break;
case BFS_SPAWN_DUP2:
if (dup2(action->in_fd, action->out_fd) < 0) {
goto fail;
}
break;
case BFS_SPAWN_FCHDIR:
if (fchdir(action->in_fd) != 0) {
goto fail;
}
break;
}
}
if (flags & BFS_SPAWN_USEPATH) {
bfs_execvpe(exe, argv, envp);
} else {
execve(exe, argv, envp);
}
fail:
error = errno;
while (write(pipefd[1], &error, sizeof(error)) < sizeof(error));
close(pipefd[1]);
_Exit(127);
}
pid_t bfs_spawn(const char *exe, const struct bfs_spawn *ctx, char **argv, char **envp) {
// Use a pipe to report errors from the child
int pipefd[2];
if (pipe_cloexec(pipefd) != 0) {
return -1;
}
int error;
pid_t pid = fork();
if (pid < 0) {
error = errno;
close(pipefd[1]);
close(pipefd[0]);
errno = error;
return -1;
} else if (pid == 0) {
// Child
bfs_spawn_exec(exe, ctx, argv, envp, pipefd);
}
// Parent
close(pipefd[1]);
ssize_t nbytes = read(pipefd[0], &error, sizeof(error));
close(pipefd[0]);
if (nbytes == sizeof(error)) {
int wstatus;
waitpid(pid, &wstatus, 0);
errno = error;
return -1;
}
return pid;
}
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