mirror of https://github.com/martanne/abduco
Fix race condition on command execution
There are now two different pipes used for synchronization purposes.
This commit is contained in:
Marc André Tanner
parent
c81c3c3214
commit
9e29a968d8
79
abduco.c
79
abduco.c
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@ -22,7 +22,6 @@
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#include <stdbool.h>
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#include <stddef.h>
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#include <signal.h>
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#include <poll.h>
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#include <libgen.h>
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#include <string.h>
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#include <limits.h>
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@ -266,12 +265,21 @@ static int create_socket(const char *name) {
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}
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static bool create_session(const char *name, char * const argv[]) {
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int pipefds[2];
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/* this uses the well known double fork strategy as described in section 1.7 of
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*
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* http://www.faqs.org/faqs/unix-faq/programmer/faq/
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*
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* pipes are used for synchronization and error reporting i.e. the child sets
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* the close on exec flag before calling execvp(3) the parent blocks on a read(2)
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* in case of failure the error message is written to the pipe, success is
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* indicated by EOF on the pipe.
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*/
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int client_pipe[2], server_pipe[2];
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pid_t pid;
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char errormsg[255];
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struct sigaction sa;
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if (pipe(pipefds) == -1)
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if (pipe(client_pipe) == -1)
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return false;
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if ((server.socket = server_create_socket(name)) == -1)
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return false;
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@ -279,28 +287,42 @@ static bool create_session(const char *name, char * const argv[]) {
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switch ((pid = fork())) {
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case 0: /* child process */
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setsid();
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close(pipefds[0]);
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close(client_pipe[0]);
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switch ((pid = fork())) {
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case 0: /* child process */
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if (pipe(server_pipe) == -1) {
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snprintf(errormsg, sizeof(errormsg), "server-pipe: %s\n", strerror(errno));
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write_all(client_pipe[1], errormsg, strlen(errormsg));
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close(client_pipe[1]);
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_exit(EXIT_FAILURE);
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}
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sa.sa_flags = 0;
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sigemptyset(&sa.sa_mask);
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sa.sa_handler = server_pty_died_handler;
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sigaction(SIGCHLD, &sa, NULL);
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switch (server.pid = forkpty(&server.pty, NULL, has_term ? &server.term : NULL, &server.winsize)) {
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case 0: /* child process */
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fcntl(pipefds[1], F_SETFD, FD_CLOEXEC);
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case 0: /* child = user application process */
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close(server.socket);
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close(server_pipe[0]);
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fcntl(client_pipe[1], F_SETFD, FD_CLOEXEC);
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fcntl(server_pipe[1], F_SETFD, FD_CLOEXEC);
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execvp(argv[0], argv);
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snprintf(errormsg, sizeof(errormsg), "server-execvp: %s\n", strerror(errno));
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write_all(pipefds[1], errormsg, strlen(errormsg));
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close(pipefds[1]);
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exit(EXIT_FAILURE);
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write_all(client_pipe[1], errormsg, strlen(errormsg));
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write_all(server_pipe[1], errormsg, strlen(errormsg));
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close(client_pipe[1]);
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close(server_pipe[1]);
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_exit(EXIT_FAILURE);
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break;
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case -1:
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die("server-forkpty");
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case -1: /* forkpty failed */
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snprintf(errormsg, sizeof(errormsg), "server-forkpty: %s\n", strerror(errno));
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write_all(client_pipe[1], errormsg, strlen(errormsg));
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close(client_pipe[1]);
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close(server_pipe[0]);
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close(server_pipe[1]);
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_exit(EXIT_FAILURE);
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break;
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default:
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/* SIGTTIN, SIGTTU */
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default: /* parent = server process */
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sa.sa_handler = server_sigterm_handler;
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sigaction(SIGTERM, &sa, NULL);
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sigaction(SIGINT, &sa, NULL);
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@ -316,33 +338,42 @@ static bool create_session(const char *name, char * const argv[]) {
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dup2(fd, 1);
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dup2(fd, 2);
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#endif /* NDEBUG */
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close(pipefds[1]);
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struct pollfd pipe_status = { .fd = pipefds[0], .events = POLLIN };
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if (poll(&pipe_status, 1, -1) == 1 && pipe_status.revents == POLLHUP)
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exit(EXIT_FAILURE);
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close(client_pipe[1]);
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close(server_pipe[1]);
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if (read_all(server_pipe[0], errormsg, sizeof(errormsg)) > 0)
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_exit(EXIT_FAILURE);
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close(server_pipe[0]);
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server_mainloop();
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break;
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}
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break;
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default:
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close(pipefds[1]);
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exit(EXIT_SUCCESS);
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case -1: /* fork failed */
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snprintf(errormsg, sizeof(errormsg), "server-fork: %s\n", strerror(errno));
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write_all(client_pipe[1], errormsg, strlen(errormsg));
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close(client_pipe[1]);
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_exit(EXIT_FAILURE);
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break;
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default: /* parent = intermediate process */
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close(client_pipe[1]);
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_exit(EXIT_SUCCESS);
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break;
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}
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break;
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case -1: /* fork failed */
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close(client_pipe[0]);
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close(client_pipe[1]);
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return false;
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default: /* parent */
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close(pipefds[1]);
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default: /* parent = client process */
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close(client_pipe[1]);
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int status;
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wait(&status); /* wait for first fork */
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ssize_t len = read_all(pipefds[0], errormsg, sizeof(errormsg));
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ssize_t len = read_all(client_pipe[0], errormsg, sizeof(errormsg));
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if (len > 0) {
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write_all(STDERR_FILENO, errormsg, len);
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unlink(sockaddr.sun_path);
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exit(EXIT_FAILURE);
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}
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close(pipefds[0]);
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close(client_pipe[0]);
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}
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return true;
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}
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