core: add "khash" API to src/basic/ (as wrapper around kernel AF_ALG)

Let's take inspiration from bluez's ELL library, and let's move our
cryptographic primitives away from libgcrypt and towards the kernel's AF_ALG
cryptographic userspace API.

In the long run we should try to remove the dependency on libgcrypt, in favour
of using only the kernel's own primitives, however this is unlikely to happen
anytime soon, as the kernel does not provide Elliptic Curve APIs to userspace
at this time, and we need them for the DNSSEC cryptographic.

This commit only covers hashing for now, symmetric encryption/decryption or
even asymetric encryption/decryption is not available for now.

"khash" is little more than a lightweight wrapper around the kernel's AF_ALG
socket API.

3 files changed, 332 insertions, 0 deletions

diff --git a/src/basic/khash.c b/src/basic/khash.c
new file mode 100644
index 0000000000..9a2a3edb75
--- /dev/null
+++ b/src/basic/khash.c
@@ -0,0 +1,275 @@
+/***
+  This file is part of systemd.
+
+  Copyright 2016 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <linux/if_alg.h>
+#include <stdbool.h>
+#include <sys/socket.h>
+
+#include "alloc-util.h"
+#include "fd-util.h"
+#include "hexdecoct.h"
+#include "khash.h"
+#include "macro.h"
+#include "missing.h"
+#include "string-util.h"
+#include "util.h"
+
+/* On current kernels the maximum digest (according to "grep digestsize /proc/crypto | sort -u") is actually 32, but
+ * let's add some extra room, the few wasted bytes don't really matter... */
+#define LONGEST_DIGEST 128
+
+struct khash {
+        int fd;
+        char *algorithm;
+        uint8_t digest[LONGEST_DIGEST+1];
+        size_t digest_size;
+        bool digest_valid;
+};
+
+int khash_new_with_key(khash **ret, const char *algorithm, const void *key, size_t key_size) {
+        union {
+                struct sockaddr sa;
+                struct sockaddr_alg alg;
+        } sa = {
+                .alg.salg_family = AF_ALG,
+                .alg.salg_type = "hash",
+        };
+
+        _cleanup_(khash_unrefp) khash *h = NULL;
+        _cleanup_close_ int fd = -1;
+        ssize_t n;
+
+        assert(ret);
+        assert(key || key_size == 0);
+
+        /* Filter out an empty algorithm early, as we do not support an algorithm by that name. */
+        if (isempty(algorithm))
+                return -EINVAL;
+
+        /* Overly long hash algorithm names we definitely do not support */
+        if (strlen(algorithm) >= sizeof(sa.alg.salg_name))
+                return -EOPNOTSUPP;
+
+        fd = socket(AF_ALG, SOCK_SEQPACKET|SOCK_CLOEXEC, 0);
+        if (fd < 0)
+                return -errno;
+
+        strcpy((char*) sa.alg.salg_name, algorithm);
+        if (bind(fd, &sa.sa, sizeof(sa)) < 0) {
+                if (errno == ENOENT)
+                        return -EOPNOTSUPP;
+                return -errno;
+        }
+
+        if (key) {
+                if (setsockopt(fd, SOL_ALG, ALG_SET_KEY, key, key_size) < 0)
+                        return -errno;
+        }
+
+        h = new0(khash, 1);
+        if (!h)
+                return -ENOMEM;
+
+        h->fd = accept4(fd, NULL, 0, SOCK_CLOEXEC);
+        if (h->fd < 0)
+                return -errno;
+
+        h->algorithm = strdup(algorithm);
+        if (!h->algorithm)
+                return -ENOMEM;
+
+        /* Temporary fix for rc kernel bug: https://bugzilla.redhat.com/show_bug.cgi?id=1395896 */
+        (void) send(h->fd, NULL, 0, 0);
+
+        /* Figure out the digest size */
+        n = recv(h->fd, h->digest, sizeof(h->digest), 0);
+        if (n < 0)
+                return -errno;
+        if (n >= LONGEST_DIGEST) /* longer than what we expected? If so, we don't support this */
+                return -EOPNOTSUPP;
+
+        h->digest_size = (size_t) n;
+        h->digest_valid = true;
+
+        /* Temporary fix for rc kernel bug: https://bugzilla.redhat.com/show_bug.cgi?id=1395896 */
+        (void) send(h->fd, NULL, 0, 0);
+
+        *ret = h;
+        h = NULL;
+
+        return 0;
+}
+
+int khash_new(khash **ret, const char *algorithm) {
+        return khash_new_with_key(ret, algorithm, NULL, 0);
+}
+
+khash* khash_unref(khash *h) {
+        if (!h)
+                return NULL;
+
+        safe_close(h->fd);
+        free(h->algorithm);
+        free(h);
+
+        return NULL;
+}
+
+int khash_dup(khash *h, khash **ret) {
+        _cleanup_(khash_unrefp) khash *copy = NULL;
+
+        assert(h);
+        assert(ret);
+
+        copy = newdup(khash, h, 1);
+        if (!copy)
+                return -ENOMEM;
+
+        copy->fd = -1;
+        copy->algorithm = strdup(h->algorithm);
+        if (!copy)
+                return -ENOMEM;
+
+        copy->fd = accept4(h->fd, NULL, 0, SOCK_CLOEXEC);
+        if (copy->fd < 0)
+                return -errno;
+
+        *ret = copy;
+        copy = NULL;
+
+        return 0;
+}
+
+const char *khash_get_algorithm(khash *h) {
+        assert(h);
+
+        return h->algorithm;
+}
+
+size_t khash_get_size(khash *h) {
+        assert(h);
+
+        return h->digest_size;
+}
+
+int khash_reset(khash *h) {
+        ssize_t n;
+
+        assert(h);
+
+        n = send(h->fd, NULL, 0, 0);
+        if (n < 0)
+                return -errno;
+
+        h->digest_valid = false;
+
+        return 0;
+}
+
+int khash_put(khash *h, const void *buffer, size_t size) {
+        ssize_t n;
+
+        assert(h);
+        assert(buffer || size == 0);
+
+        if (size <= 0)
+                return 0;
+
+        n = send(h->fd, buffer, size, MSG_MORE);
+        if (n < 0)
+                return -errno;
+
+        h->digest_valid = false;
+
+        return 0;
+}
+
+int khash_put_iovec(khash *h, const struct iovec *iovec, size_t n) {
+        struct msghdr mh = {
+                mh.msg_iov = (struct iovec*) iovec,
+                mh.msg_iovlen = n,
+        };
+        ssize_t k;
+
+        assert(h);
+        assert(iovec || n == 0);
+
+        if (n <= 0)
+                return 0;
+
+        k = sendmsg(h->fd, &mh, MSG_MORE);
+        if (k < 0)
+                return -errno;
+
+        h->digest_valid = false;
+
+        return 0;
+}
+
+static int retrieve_digest(khash *h) {
+        ssize_t n;
+
+        assert(h);
+
+        if (h->digest_valid)
+                return 0;
+
+        n = recv(h->fd, h->digest, h->digest_size, 0);
+        if (n < 0)
+                return n;
+        if ((size_t) n != h->digest_size) /* digest size changed? */
+                return -EIO;
+
+        h->digest_valid = true;
+
+        return 0;
+}
+
+int khash_digest_data(khash *h, const void **ret) {
+        int r;
+
+        assert(h);
+        assert(ret);
+
+        r = retrieve_digest(h);
+        if (r < 0)
+                return r;
+
+        *ret = h->digest;
+        return 0;
+}
+
+int khash_digest_string(khash *h, char **ret) {
+        int r;
+        char *p;
+
+        assert(h);
+        assert(ret);
+
+        r = retrieve_digest(h);
+        if (r < 0)
+                return r;
+
+        p = hexmem(h->digest, h->digest_size);
+        if (!p)
+                return -ENOMEM;
+
+        *ret = p;
+        return 0;
+}
diff --git a/src/basic/khash.h b/src/basic/khash.h
new file mode 100644
index 0000000000..f404a68236
--- /dev/null
+++ b/src/basic/khash.h
@@ -0,0 +1,53 @@
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2016 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <inttypes.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+
+#include "macro.h"
+
+typedef struct khash khash;
+
+/* For plain hash functions. Hash functions commonly supported on today's kernels are: crc32c, crct10dif, crc32,
+ * sha224, sha256, sha512, sha384, sha1, md5, md4, sha3-224, sha3-256, sha3-384, sha3-512, and more.*/
+int khash_new(khash **ret, const char *algorithm);
+
+/* For keyed hash functions. Hash functions commonly supported on today's kernels are: hmac(sha256), cmac(aes),
+ * cmac(des3_ede), hmac(sha3-512), hmac(sha3-384), hmac(sha3-256), hmac(sha3-224), hmac(rmd160), hmac(rmd128),
+ * hmac(sha224), hmac(sha512), hmac(sha384), hmac(sha1), hmac(md5), and more. */
+int khash_new_with_key(khash **ret, const char *algorithm, const void *key, size_t key_size);
+
+int khash_dup(khash *h, khash **ret);
+khash* khash_unref(khash *h);
+
+const char *khash_get_algorithm(khash *h);
+size_t khash_get_size(khash *h);
+
+int khash_reset(khash *h);
+
+int khash_put(khash *h, const void *buffer, size_t size);
+int khash_put_iovec(khash *h, const struct iovec *iovec, size_t n);
+
+int khash_digest_data(khash *h, const void **ret);
+int khash_digest_string(khash *h, char **ret);
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(khash*, khash_unref);
diff --git a/src/basic/missing.h b/src/basic/missing.h
index 8833617dc6..1502b3f4f4 100644
--- a/src/basic/missing.h
+++ b/src/basic/missing.h
@@ -1109,4 +1109,8 @@ struct ethtool_link_settings {
 
 #endif
 
+#ifndef SOL_ALG
+#define SOL_ALG 279
+#endif
+
 #include "missing_syscall.h"