Refactor command execution to not use tempfile

Previously, we wrote the passphrase contents to a temporary file on
/dev/shm and then wiped it afterwards. This is odd, why don't we use a
pipe for this purpose, like it's intended to be used? Replace all of
that previous code by piped IPC.

client.c

@@ -65,7 +65,7 @@ static bool unlock_luks_volume(const struct volume_entry_t *volume, const struct
 	bool success = true;
 	char luks_passphrase[LUKS_PASSPHRASE_TEXT_SIZE_BYTES];
 	if (ascii_encode(luks_passphrase, sizeof(luks_passphrase), unlock_msg->luks_passphrase_raw, sizeof(unlock_msg->luks_passphrase_raw))) {
-		success = open_luks_device_pw(volume->volume_uuid, volume->devmapper_name, luks_passphrase, strlen(luks_passphrase));
+		success = open_luks_device(volume->volume_uuid, volume->devmapper_name, luks_passphrase, strlen(luks_passphrase));
 	} else {
 		log_msg(LLVL_FATAL, "Failed to transcribe raw LUKS passphrase to text form.");
 		success = false;

exec.c

@@ -1,6 +1,6 @@
 /*
 	luksrku - Tool to remotely unlock LUKS disks using TLS.
-	Copyright (C) 2016-2016 Johannes Bauer
+	Copyright (C) 2016-2019 Johannes Bauer
 
 	This file is part of luksrku.
 
@@ -27,6 +27,7 @@
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <string.h>
+#include <stdint.h>
 #include <errno.h>
 
 #include "exec.h"
@@ -78,45 +79,80 @@ static char **argv_dup(const char **argv) {
 	return result;
 }
 
-struct runresult_t exec_command(const char **argv, bool show_output) {
+struct exec_result_t exec_command(const struct exec_cmd_t *command) {
-	struct runresult_t runresult;
+	char **argvcopy = argv_dup(command->argv);
-	char **argvcopy = argv_dup(argv);
+	if (!argvcopy) {
+		return (struct exec_result_t) { .success = false };
+	}
 
-	memset(&runresult, 0, sizeof(runresult));
+	int pipefd[2];
+	if (pipe(pipefd) == -1) {
+		log_libc(LLVL_ERROR, "Creation of pipe(2) failed trying to execute %s", argvcopy[0]);
+		argv_free(argvcopy);
+		return (struct exec_result_t) { .success = false };
+	}
+	const int pipe_read_end = pipefd[0];
+	const int pipe_write_end = pipefd[1];
 
 	pid_t pid = fork();
 	if (pid == -1) {
 		perror("fork");
-		runresult.success = false;
 		argv_free(argvcopy);
-		return runresult;
+		return (struct exec_result_t) { .success = false };
 	}
 	if (pid == 0) {
 		/* Child */
-		if (!show_output) {
+
+		close(pipe_write_end);
+		if (dup2(pipe_read_end, STDIN_FILENO) == -1) {
+			log_libc(LLVL_ERROR, "Could not dup2(2) stdin while trying to execute %s", argvcopy[0]);
+			exit(EXIT_FAILURE);
+		}
+
+		if (!command->show_output) {
 			/* Shut up the child if user did not request debug output */
-			close(1);
+			close(STDOUT_FILENO);
-			close(2);
+			close(STDERR_FILENO);
 		}
 		execvp(argvcopy[0], argvcopy);
 		log_libc(LLVL_ERROR, "Execution of %s in forked child process failed execvp(3)", argvcopy[0]);
 
-		/* Exec failed, terminate child with EXIT_FAILUR (parent will catch
+		/* Exec failed, terminate child with EXIT_FAILURE (parent will catch
 		 * this as the return code) */
 		exit(EXIT_FAILURE);
 	}
 
+	/* Parent process */
+	struct exec_result_t runresult = {
+		.success = true,
+	};
+	close(pipe_read_end);
+
+	if (command->stdin_data && command->stdin_length) {
+		unsigned int offset = 0;
+		unsigned int remaining_bytes = command->stdin_length;
+		const uint8_t *byte_buffer = (const uint8_t*)command->stdin_data;
+		while (remaining_bytes) {
+			ssize_t written = write(pipe_write_end, byte_buffer + offset, remaining_bytes);
+			if (written <= 0) {
+				log_libc(LLVL_ERROR, "writing to pipe returned %d", written);
+				runresult.success = false;
+			}
+			offset += written;
+			remaining_bytes -= written;
+		}
+	}
+	close(pipe_write_end);
+
 	int status;
 	if (waitpid(pid, &status, 0) == (pid_t)-1) {
 		log_libc(LLVL_ERROR, "exec_command %s failed executing waitpid(2)", argvcopy[0]);
 		runresult.success = false;
-		runresult.returncode = -1;
 	} else {
-		runresult.success = true;
 		runresult.returncode = WEXITSTATUS(status);
 	}
 	argv_free(argvcopy);
-	log_msg(LLVL_DEBUG, "Subprocess (PID %d): %s exited with returncode %d", pid, argv[0], runresult.returncode);
+	log_msg(LLVL_DEBUG, "Subprocess (PID %d): %s exited with returncode %d", pid, command->argv[0], runresult.returncode);
 	return runresult;
 }
 

exec.h

@@ -1,6 +1,6 @@
 /*
 	luksrku - Tool to remotely unlock LUKS disks using TLS.
-	Copyright (C) 2016-2016 Johannes Bauer
+	Copyright (C) 2016-2019 Johannes Bauer
 
 	This file is part of luksrku.
 
@@ -26,14 +26,21 @@
 
 #include <stdbool.h>
 
-struct runresult_t {
+struct exec_cmd_t {
+	const char **argv;
+	bool show_output;
+	const void *stdin_data;
+	unsigned int stdin_length;
+};
+
+struct exec_result_t {
 	bool success;
 	int returncode;
 };
 
 /*************** AUTO GENERATED SECTION FOLLOWS ***************/
 void argv_dump(const char **argv);
-struct runresult_t exec_command(const char **argv, bool show_output);
+struct exec_result_t exec_command(const struct exec_cmd_t *cmd);
 /***************  AUTO GENERATED SECTION ENDS   ***************/
 
 #endif

luks.c

@@ -37,85 +37,38 @@
 #include "uuid.h"
 
 bool is_luks_device_opened(const char *mapping_name) {
-	const char *command[] = {
+	struct exec_cmd_t cmd = {
+		.argv = (const char *[]){
 			"dmsetup",
 			"status",
 			mapping_name,
 			NULL,
+		},
+		.show_output = should_log(LLVL_TRACE),
 	};
-	struct runresult_t runresult = exec_command(command, should_log(LLVL_TRACE));
+	struct exec_result_t runresult = exec_command(&cmd);
 	return runresult.success && (runresult.returncode == 0);
 }
 
-bool open_luks_device(const uint8_t *encrypted_device_uuid, const char *mapping_name, const char *passphrase_file) {
+bool open_luks_device(const uint8_t *encrypted_device_uuid, const char *mapping_name, const char *passphrase, unsigned int passphrase_length) {
 	char encrypted_device[64];
 	strcpy(encrypted_device, "UUID=");
 	sprintf_uuid(encrypted_device + 5, encrypted_device_uuid);
 	log_msg(LLVL_INFO, "Trying to unlock LUKS mapping %s based on %s", mapping_name, encrypted_device);
 
-	const char *command[] = {
+	struct exec_cmd_t cmd = {
+		.argv = (const char *[]){
 			"cryptsetup",
 			"luksOpen",
 			"-T", "1",
-		"-d", passphrase_file,
 			encrypted_device,
 			mapping_name,
 			NULL,
-
+		},
+		.stdin_data = passphrase,
+		.stdin_length = passphrase_length,
+		.show_output = should_log(LLVL_DEBUG),
 	};
-	struct runresult_t runresult = exec_command(command, should_log(LLVL_DEBUG));
+	struct exec_result_t runresult = exec_command(&cmd);
 	return runresult.success && (runresult.returncode == 0);
 }
-
-static bool wipe_passphrase_file(const char *filename, int length) {
-	uint8_t wipe_buf[length];
-	memset(wipe_buf, 0, length);
-
-	int fd = open(filename, O_WRONLY);
-	if (fd == -1) {
-		log_libc(LLVL_ERROR, "Wiping of passphrase file %s failed in open(2)", filename);
-		return false;
-	}
-
-	if (write(fd, wipe_buf, length) != length) {
-		log_libc(LLVL_ERROR, "Wiping of passphrase file %s failed in write(2)", filename);
-		close(fd);
-		return false;
-	}
-	close(fd);
-	unlink(filename);
-	return true;
-}
-
-static const char *write_passphrase_file(const void *passphrase, int passphrase_length) {
-	//const char *filename = "/dev/shm/luksrku_passphrase.bin";		/* TODO make this variable */
-	const char *filename = "/tmp/luksrku_passphrase.bin";
-	int fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC, 0600);
-	if (fd == -1) {
-		log_libc(LLVL_ERROR, "Creation of passphrase file %s failed", filename);
-		return NULL;
-	}
-
-	if (write(fd, passphrase, passphrase_length) != passphrase_length) {
-		log_libc(LLVL_ERROR, "Writing to passphrase file %s failed", filename);
-		wipe_passphrase_file(filename, passphrase_length);
-		close(fd);
-		return NULL;
-	}
-
-	close(fd);
-	return filename;
-}
-
-bool open_luks_device_pw(const uint8_t *encrypted_device_uuid, const char *mapping_name, const char *passphrase, unsigned int passphrase_length) {
-	const char *pw_filename = write_passphrase_file(passphrase, passphrase_length);
-	if (!pw_filename) {
-		return false;
-	}
-	bool success = open_luks_device(encrypted_device_uuid, mapping_name, pw_filename);
-	if (!wipe_passphrase_file(pw_filename, passphrase_length)) {
-		log_libc(LLVL_ERROR, "Wiping of passphrase file failed -- treating this unlock as failed (luksOpen %s)", success ? "succeeded" : "also failed");
-		success = false;
-	}
-	return success;
-}

luks.h

@@ -29,8 +29,7 @@
 
 /*************** AUTO GENERATED SECTION FOLLOWS ***************/
 bool is_luks_device_opened(const char *mapping_name);
-bool open_luks_device(const uint8_t *encrypted_device_uuid, const char *mapping_name, const char *passphrase_file);
+bool open_luks_device(const uint8_t *encrypted_device_uuid, const char *mapping_name, const char *passphrase, unsigned int passphrase_length);
-bool open_luks_device_pw(const uint8_t *encrypted_device_uuid, const char *mapping_name, const char *passphrase, unsigned int passphrase_length);
 /***************  AUTO GENERATED SECTION ENDS   ***************/
 
 #endif