Close FILE structs after forking

Fixes #48

shell/task/assignment.c

@@ -39,7 +39,7 @@ static int task_assignment_poll(struct task *task, struct context *ctx) {
 		free(new_value);
 	}
 
-	return 0;
+	return EXIT_SUCCESS;
 }
 
 static const struct task_interface task_assignment_impl = {

shell/task/async.c

@@ -21,12 +21,17 @@ static void task_async_destroy(struct task *task) {
 	free(ta);
 }
 
-static int fork_detached(void) {
+static int fork_detached(struct context *ctx) {
 	pid_t pid = fork();
 	if (pid < 0) {
 		fprintf(stderr, "failed to fork(): %s\n", strerror(errno));
 		return -1;
 	} else if (pid == 0) {
+		// On exit, libc cleans up FILE structs, and can seek the backing FD if
+		// some data has been buffered. This messes up the parent's FD too. To
+		// prevent this from hapening, close all FILE structs.
+		fclose(ctx->state->input);
+
 		pid_t child_pid = fork();
 		if (child_pid < 0) {
 			fprintf(stderr, "failed to fork(): %s\n", strerror(errno));
@@ -50,7 +55,7 @@ static bool task_async_start(struct task *task, struct context *ctx) {
 	struct task_async *ta = (struct task_async *)task;
 
 	// Start a subshell
-	int ret = fork_detached();
+	int ret = fork_detached(ctx);
 	if (ret < 0) {
 		return false;
 	} else if (ret == 0) {

shell/task/command_process.c

@@ -79,6 +79,11 @@ static bool task_process_start(struct task_command *tc, struct context *ctx) {
 		fprintf(stderr, "failed to fork(): %s\n", strerror(errno));
 		return false;
 	} else if (pid == 0) {
+		// On exit, libc cleans up FILE structs, and can seek the backing FD if
+		// some data has been buffered. This messes up the parent's FD too. To
+		// prevent this from hapening, close all FILE structs.
+		fclose(ctx->state->input);
+
 		for (size_t i = 0; i < sc->assignments.len; ++i) {
 			struct mrsh_assignment *assign = sc->assignments.data[i];
 			uint32_t prev_attribs;

shell/task/subshell.c

@@ -25,6 +25,11 @@ static bool task_subshell_start(struct task_subshell *ts, struct context *ctx) {
 		fprintf(stderr, "failed to fork(): %s\n", strerror(errno));
 		return false;
 	} else if (pid == 0) {
+		// On exit, libc cleans up FILE structs, and can seek the backing FD if
+		// some data has been buffered. This messes up the parent's FD too. To
+		// prevent this from hapening, close all FILE structs.
+		fclose(ctx->state->input);
+
 		errno = 0;
 		int ret = task_run(ts->subtask, ctx);
 		if (ret < 0) {

shell/task/word.c

@@ -30,7 +30,7 @@ struct task_word {
 
 static bool read_full(int fd, char *buf, size_t size) {
 	size_t n_read = 0;
-	do {
+	while (n_read < size) {
 		ssize_t n = read(fd, buf, size - n_read);
 		if (n < 0 && errno == EINTR) {
 			continue;
@@ -39,7 +39,7 @@ static bool read_full(int fd, char *buf, size_t size) {
 			return false;
 		}
 		n_read += n;
-	} while (n_read < size);
+	}
 	return true;
 }
 
@@ -66,7 +66,13 @@ static bool task_word_command_start(struct task_word *tt,
 		fprintf(stderr, "failed to fork(): %s\n", strerror(errno));
 		return false;
 	} else if (pid == 0) {
+		// On exit, libc cleans up FILE structs, and can seek the backing FD if
+		// some data has been buffered. This messes up the parent's FD too. To
+		// prevent this from hapening, close all FILE structs.
+		fclose(ctx->state->input);
+
 		dup2(fd, STDOUT_FILENO);
+		close(fd);
 
 		if (ctx->stdin_fileno >= 0) {
 			close(ctx->stdin_fileno);