1 files changed, 418 insertions, 0 deletions
diff --git a/bin/worker.c b/bin/worker.c
new file mode 100644
index 0000000..ef0cefc
--- /dev/null
+++ b/bin/worker.c
@@ -0,0 +1,418 @@
+/*
+ * (C) 2014-2017 by Christian Hesse <mail@eworm.de>
+ *
+ * This software may be used and distributed according to the terms
+ * of the GNU General Public License, incorporated herein by reference.
+ *
+ * compile with:
+ * $ gcc -o ykfde ykfde.c -liniparser -lkeyutils -lykpers-1 -lyubikey
+ *
+ * test with:
+ * $ systemd-ask-password --no-tty "Please enter passphrase for disk foobar..."
+ */
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/poll.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#include <iniparser.h>
+
+#include <keyutils.h>
+
+#include <yubikey.h>
+#include <ykpers-1/ykdef.h>
+#include <ykpers-1/ykcore.h>
+
+#include "../config.h"
+
+/* Yubikey supports write of 64 byte challenge to slot,
+ * returns HMAC-SHA1 response.
+ *
+ * Lengths are defined in ykpers-1/ykdef.h:
+ * SHA1_MAX_BLOCK_SIZE     64
+ * SHA1_DIGEST_SIZE        20
+ *
+ * For passphrase we use hex encoded digest, that is
+ * twice the length of binary digest. */
+#define CHALLENGELEN	SHA1_MAX_BLOCK_SIZE
+#define RESPONSELEN	SHA1_MAX_BLOCK_SIZE
+#define PASSPHRASELEN	SHA1_DIGEST_SIZE * 2
+
+#define ASK_PATH	"/run/systemd/ask-password/"
+#define ASK_MESSAGE	"Please enter passphrase for disk"
+
+/*** send_on_socket ***/
+static int send_on_socket(int fd, const char *socket_name, const void *packet, size_t size) {
+	union {
+		struct sockaddr sa;
+		struct sockaddr_un un;
+	} sa = {
+		.un.sun_family = AF_UNIX,
+	};
+
+	strncpy(sa.un.sun_path, socket_name, sizeof(sa.un.sun_path));
+
+	if (sendto(fd, packet, size, MSG_NOSIGNAL, &sa.sa, offsetof(struct sockaddr_un, sun_path) + strlen(socket_name)) < 0) {
+		perror("sendto() failed");
+		return EXIT_FAILURE;
+	}
+
+	return EXIT_SUCCESS;
+}
+
+/*** yk_open_and_check ***/
+static YK_KEY * yk_open_and_check(const unsigned int expected, unsigned int * serial) {
+	YK_KEY * yk;
+
+	if ((yk = yk_open_first_key()) == NULL) {
+		if (errno != EAGAIN)
+			perror("yk_open_first_key() failed");
+		goto out1;
+	}
+
+	if (serial != NULL) {
+		/* read the serial number from key */
+		if (yk_get_serial(yk, 0, 0, serial) == 0) {
+			perror("yk_get_serial() failed");
+			goto out2;
+		}
+
+		if (expected > 0 && expected != *serial) {
+			fprintf(stderr, "Opened Yubikey with unexpected serial number (%d != %d)...\n", expected, *serial);
+			goto out2;
+		}
+	}
+
+	return yk;
+
+out2:
+	/* close Yubikey */
+	if (yk_close_key(yk) == 0)
+		perror("yk_close_key() failed");
+
+out1:
+	return NULL;
+}
+
+/*** read_challenge ***/
+static int read_challenge(const unsigned int serial, char * challenge) {
+	int rc = EXIT_FAILURE;
+	char challengefilename[sizeof(CHALLENGEDIR) + 11 /* "/challenge-" */ + 10 /* unsigned int in char */ + 1];
+	int challengefile;
+
+	snprintf(challengefilename, sizeof(challengefilename), CHALLENGEDIR "/challenge-%d", serial);
+
+	/* check if challenge file exists */
+	if (access(challengefilename, R_OK) == -1) {
+		goto out1;
+	}
+
+	/* read challenge from file */
+	if ((challengefile = open(challengefilename, O_RDONLY)) < 0) {
+		perror("Failed opening challenge file for reading");
+		goto out1;
+	}
+
+	if (read(challengefile, challenge, CHALLENGELEN) < 0) {
+		perror("Failed reading challenge from file");
+		goto out2;
+	}
+
+	rc = EXIT_SUCCESS;
+
+out2:
+	close(challengefile);
+
+out1:
+	return rc;
+}
+
+/*** get_second_factor ***/
+static char * get_second_factor(void) {
+	key_serial_t key;
+	void * payload = NULL;
+
+	/* get second factor from key store
+	 * If this fails it is not critical... possibly we just do not
+	 * use second factor. */
+	key = keyctl_search(KEY_SPEC_USER_KEYRING, "user", "ykfde-2f", 0);
+
+	if (key > 0) {
+		/* if we have a key id we have a key - so this should succeed */
+		if (keyctl_read_alloc(key, &payload) < 0) {
+			perror("Failed reading payload from key");
+			return NULL;
+		}
+
+		return payload;
+	}
+
+	return NULL;
+}
+
+/*** get_response ***/
+static int get_response(const unsigned int serial, uint8_t slot, char * challenge, char * passphrase) {
+	YK_KEY * yk;
+	char response[RESPONSELEN];
+	char * second_factor;
+	size_t second_factor_len;
+	/* iniparser */
+	dictionary * ini;
+	char section_ykslot[10 /* unsigned int in char */ + 1 + sizeof(CONFYKSLOT) + 1];
+
+	memset(response, 0, RESPONSELEN);
+
+	if ((second_factor = get_second_factor()) != NULL) {
+		/* we replace part of the challenge with the second factor */
+		second_factor_len = strlen(second_factor);
+		memcpy(challenge, second_factor, second_factor_len < CHALLENGELEN / 2 ?
+				second_factor_len : CHALLENGELEN / 2);
+		memset(second_factor, 0, second_factor_len);
+		free(second_factor);
+	}
+
+	/* try to read config file
+	 * If anything here fails we do not care... slot 2 is the default. */
+	if ((ini = iniparser_load(CONFIGFILE)) != NULL) {
+		/* first try the general setting */
+		slot = iniparser_getint(ini, "general:" CONFYKSLOT, slot);
+
+		sprintf(section_ykslot, "%d:" CONFYKSLOT, serial);
+
+		/* then probe for setting with serial number */
+		slot = iniparser_getint(ini, section_ykslot, slot);
+
+		switch (slot) {
+			case 1:
+			case SLOT_CHAL_HMAC1:
+				slot = SLOT_CHAL_HMAC1;
+				break;
+			case 2:
+			case SLOT_CHAL_HMAC2:
+			default:
+				slot = SLOT_CHAL_HMAC2;
+				break;
+		}
+
+		iniparser_freedict(ini);
+	}
+
+	/* open Yubikey and check serial */
+	if ((yk = yk_open_and_check(serial, NULL)) == NULL) {
+		fprintf(stderr, "yk_open_and_check() failed\n");
+		goto out1;
+	}
+
+	/* do challenge/response and encode to hex */
+	if (yk_challenge_response(yk, slot, true,
+			CHALLENGELEN, (unsigned char *) challenge,
+			RESPONSELEN, (unsigned char *) response) == 0) {
+		perror("yk_challenge_response() failed");
+		goto out2;
+	}
+
+	yubikey_hex_encode((char *) passphrase, (char *) response, SHA1_DIGEST_SIZE);
+
+out2:
+	/* close Yubikey */
+	if (yk_close_key(yk) == 0)
+		perror("yk_close_key() failed");
+
+out1:
+	memset(response, 0, RESPONSELEN);
+
+	return EXIT_SUCCESS;
+}
+
+/*** add_keyring ***/
+static int add_keyring(const char * passphrase) {
+	key_serial_t key;
+
+	/* add key to kernel key store
+	 * Put it into session keyring first, set permissions and
+	 * move it to user keyring. */
+	if ((key = add_key("user", "cryptsetup", passphrase,
+			PASSPHRASELEN, KEY_SPEC_SESSION_KEYRING)) < 0) {
+		perror("add_key() failed");
+		return -1;
+	}
+
+	if (keyctl_set_timeout(key, 150) < 0) {
+		perror("keyctl_set_timeout() failed");
+		return -1;
+	}
+
+	if (keyctl_setperm(key, KEY_POS_ALL|KEY_USR_ALL) < 0) {
+		perror("keyctl_setperm() failed");
+		return -1;
+	}
+
+	if (keyctl_link(key, KEY_SPEC_USER_KEYRING) < 0) {
+		perror("keyctl_link() failed");
+		return -1;
+	}
+
+	if (keyctl_unlink(key, KEY_SPEC_SESSION_KEYRING) < 0) {
+		perror("keyctl_unlink() failed");
+		return -1;
+	}
+
+	return EXIT_SUCCESS;
+}
+
+/*** answer_askpass ***/
+static int answer_askpass(const char * ask_file, const char * passphrase) {
+	int rc = EXIT_FAILURE, fd_askpass;
+	const char * ask_message, * ask_socket;
+	/* iniparser */
+	dictionary * ini;
+
+	if ((ini = iniparser_load(ask_file)) == NULL) {
+		perror("cannot parse file");
+		goto out1;
+	}
+
+	ask_message = iniparser_getstring(ini, "Ask:Message", NULL);
+
+	if (strncmp(ask_message, ASK_MESSAGE, strlen(ASK_MESSAGE)) != 0)
+		goto out2;
+
+	if ((ask_socket = iniparser_getstring(ini, "Ask:Socket", NULL)) == NULL) {
+		perror("Could not get socket name");
+		goto out2;
+	}
+
+	if ((fd_askpass = socket(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0)) < 0) {
+		perror("socket() failed");
+		goto out2;
+	}
+
+	if (send_on_socket(fd_askpass, ask_socket, passphrase, PASSPHRASELEN + 1) < 0) {
+		perror("send_on_socket() failed");
+		goto out3;
+	}
+
+	rc = EXIT_SUCCESS;
+
+out3:
+	close(fd_askpass);
+
+out2:
+	iniparser_freedict(ini);
+
+out1:
+	return rc;
+}
+
+/*** walk_askpass ***/
+static int walk_askpass(const char * passphrase) {
+	int rc = EXIT_FAILURE;
+	DIR * dir;
+	struct dirent * ent;
+
+	/* change to directory so we do not have to assemble complete/absolute path */
+	if (chdir(ASK_PATH) != 0) {
+		perror("chdir() failed");
+		return rc;
+	}
+
+	/* Is the request already there? */
+	if ((dir = opendir(ASK_PATH)) != NULL) {
+		while ((ent = readdir(dir)) != NULL) {
+			if (strncmp(ent->d_name, "ask.", 4) == 0) {
+				if ((rc = answer_askpass(ent->d_name, passphrase)) == EXIT_SUCCESS)
+					goto out;
+			}
+		}
+	} else {
+		perror ("opendir() failed");
+		return EXIT_FAILURE;
+	}
+
+	rc = EXIT_SUCCESS;
+
+out:
+	closedir(dir);
+
+	return rc;
+}
+
+/*** main ***/
+int main(int argc, char **argv) {
+	int8_t rc = EXIT_FAILURE;
+	/* Yubikey */
+	YK_KEY * yk;
+	uint8_t slot = SLOT_CHAL_HMAC2;
+	unsigned int serial = 0;
+	/* challenge and passphrase */
+	char challenge[CHALLENGELEN + 1];
+	char passphrase[PASSPHRASELEN + 2];
+
+#ifdef DEBUG
+	/* reopening stderr to /dev/console may help debugging... */
+	FILE * tmp = freopen("/dev/console", "w", stderr);
+	(void) tmp;
+#endif
+
+	/* initialize static memory */
+	memset(challenge, 0, CHALLENGELEN + 1);
+	memset(passphrase, 0, PASSPHRASELEN + 2);
+
+	*passphrase = '+';
+
+	/* init and open first Yubikey */
+	if (yk_init() == 0) {
+		perror("yk_init() failed");
+		goto out10;
+	}
+
+	/* open Yubikey and get serial */
+	if ((yk = yk_open_and_check(0, &serial)) == NULL) {
+		if (errno == EAGAIN)
+			rc = EXIT_SUCCESS;
+		goto out30;
+	}
+
+	/* close Yubikey */
+	if (yk_close_key(yk) == 0) {
+		perror("yk_close_key() failed");
+		goto out30;
+	}
+
+	if ((rc = read_challenge(serial, challenge)) < 0)
+		goto out30;
+
+	if ((rc = get_response(serial, slot, challenge, passphrase + 1)) < 0)
+		goto out30;
+
+	if ((rc = add_keyring(passphrase + 1)) < 0)
+		goto out30;
+
+	if ((rc = walk_askpass(passphrase)) < 0)
+		goto out30;
+
+out30:
+	/* release Yubikey */
+	if (yk_release() == 0)
+		perror("yk_release() failed");
+
+out10:
+	/* wipe challenge from memory */
+	memset(challenge, 0, CHALLENGELEN + 1);
+	memset(passphrase, 0, PASSPHRASELEN + 2);
+
+	return rc;
+}
+
+// vim: set syntax=c: