From e0e3ee7aeb2d4043149a728e431a9dda949ceed5 Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Thu, 17 Nov 2016 17:07:46 +0100 Subject: [PATCH] sd-id128: add new sd_id128_get_machine_app_specific() API This adds an API for retrieving an app-specific machine ID to sd-id128. Internally it calculates HMAC-SHA256 with an 128bit app-specific ID as payload and the machine ID as key. (An alternative would have been to use siphash for this, which is also cryptographically strong. However, as it only generates 64bit hashes it's not an obvious choice for generating 128bit IDs.) Fixes: #4667 --- man/sd_id128_get_machine.xml | 65 ++++++++++++++++++++++++------ src/libelogind/libelogind.sym | 5 +++ src/libelogind/sd-id128/sd-id128.c | 31 ++++++++++++++ 3 files changed, 89 insertions(+), 12 deletions(-) diff --git a/man/sd_id128_get_machine.xml b/man/sd_id128_get_machine.xml index cd6c39032..e7326422b 100644 --- a/man/sd_id128_get_machine.xml +++ b/man/sd_id128_get_machine.xml @@ -44,6 +44,7 @@ sd_id128_get_machine + sd_id128_get_machine_app_specific sd_id128_get_boot sd_id128_get_invocation Retrieve 128-bit IDs @@ -58,6 +59,12 @@ sd_id128_t *ret + + int sd_id128_get_machine_app_specific + sd_id128_t app_id + sd_id128_t *ret + + int sd_id128_get_boot sd_id128_t *ret @@ -74,11 +81,22 @@ Description - sd_id128_get_machine() returns the - machine ID of the executing host. This reads and parses the - machine-id5 - file. This function caches the machine ID internally to make - retrieving the machine ID a cheap operation. + sd_id128_get_machine() returns the machine ID of the executing host. This reads and + parses the machine-id5 + file. This function caches the machine ID internally to make retrieving the machine ID a cheap operation. This ID + may be used wherever a unique identifier for the local system is needed. However, it is recommended to use this ID + as-is only in trusted environments. In untrusted environments it is recommended to derive an application specific + ID from this machine ID, in an irreversable (cryptographically secure) way. To make this easy + sd_id128_get_machine_app_specific() is provided, see below. + + sd_id128_get_machine_app_specific() is similar to + sd_id128_get_machine(), but retrieves a machine ID that is specific to the application that is + identified by the indicated application ID. It is recommended to use this function instead of + sd_id128_get_machine() when passing an ID to untrusted environments, in order to make sure + that the original machine ID may not be determined externally. The application-specific ID should be generated via + a tool like journalctl --new-id128, and may be compiled into the application. This function will + return the same application-specific ID for each combination of machine ID and application ID. Internally, this + function calculates HMAC-SHA256 of the application ID, keyed by the machine ID. sd_id128_get_boot() returns the boot ID of the executing kernel. This reads and parses the @@ -95,10 +113,10 @@ systemd.exec5 for details. The ID is cached internally. In future a different mechanism to determine the invocation ID may be added. - Note that sd_id128_get_boot() and sd_id128_get_invocation() always - return UUID v4 compatible IDs. sd_id128_get_machine() will also return a UUID v4-compatible - ID on new installations but might not on older. It is possible to convert the machine ID into a UUID v4-compatible - one. For more information, see + Note that sd_id128_get_machine_app_specific(), sd_id128_get_boot() + and sd_id128_get_invocation() always return UUID v4 compatible IDs. + sd_id128_get_machine() will also return a UUID v4-compatible ID on new installations but might + not on older. It is possible to convert the machine ID into a UUID v4-compatible one. For more information, see machine-id5. For more information about the sd_id128_t @@ -117,12 +135,35 @@ Notes - The sd_id128_get_machine(), sd_id128_get_boot() and - sd_id128_get_invocation() interfaces are available as a shared library, which can be compiled - and linked to with the libsystemd The sd_id128_get_machine(), sd_id128_get_machine_app_specific() + sd_id128_get_boot() and sd_id128_get_invocation() interfaces are + available as a shared library, which can be compiled and linked to with the + libsystemd pkg-config1 file. + + Examples + + + Application-specific machine ID + + Here's a simple example for an application specific machine ID: + + #include <systemd/sd-id128.h> +#include <stdio.h> + +#define OUR_APPLICATION_ID SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97) + +int main(int argc, char *argv[]) { + sd_id128_t id; + sd_id128_get_machine_app_specific(OUR_APPLICATION_ID, &id); + printf("Our application ID: " SD_ID128_FORMAT_STR "\n", SD_ID128_FORMAT_VAL(id)); + return 0; +} + + + See Also diff --git a/src/libelogind/libelogind.sym b/src/libelogind/libelogind.sym index e10e2b4a7..4f2466669 100644 --- a/src/libelogind/libelogind.sym +++ b/src/libelogind/libelogind.sym @@ -523,3 +523,8 @@ global: /* sd_bus_get_exit_on_disconnect; */ sd_id128_get_invocation; } LIBSYSTEMD_231; + +LIBSYSTEMD_233 { +global: + sd_id128_get_machine_app_specific; +} LIBSYSTEMD_232; diff --git a/src/libelogind/sd-id128/sd-id128.c b/src/libelogind/sd-id128/sd-id128.c index d4450c70a..43cc86f43 100644 --- a/src/libelogind/sd-id128/sd-id128.c +++ b/src/libelogind/sd-id128/sd-id128.c @@ -181,3 +181,34 @@ _public_ int sd_id128_randomize(sd_id128_t *ret) { *ret = make_v4_uuid(t); return 0; } + +_public_ int sd_id128_get_machine_app_specific(sd_id128_t app_id, sd_id128_t *ret) { + _cleanup_(khash_unrefp) khash *h = NULL; + sd_id128_t m, result; + const void *p; + int r; + + assert_return(ret, -EINVAL); + + r = sd_id128_get_machine(&m); + if (r < 0) + return r; + + r = khash_new_with_key(&h, "hmac(sha256)", &m, sizeof(m)); + if (r < 0) + return r; + + r = khash_put(h, &app_id, sizeof(app_id)); + if (r < 0) + return r; + + r = khash_digest_data(h, &p); + if (r < 0) + return r; + + /* We chop off the trailing 16 bytes */ + memcpy(&result, p, MIN(khash_get_size(h), sizeof(result))); + + *ret = make_v4_uuid(result); + return 0; +} -- 2.30.2