libsystemd provides a sd_id128_get_machine_app_specific() function that allows deriving an application specific UUID without directly leaking the machine ID.
Let's provide an equivalent for barebox that will be used in a following commit to generate a stable MAC instead of randomizing it. Signed-off-by: Ahmad Fatoum <[email protected]> --- common/machine_id.c | 84 ++++++++++++++++++++++++++++++++++++++++++-- include/linux/uuid.h | 8 +++++ include/machine_id.h | 10 ++++++ 3 files changed, 100 insertions(+), 2 deletions(-) diff --git a/common/machine_id.c b/common/machine_id.c index 8c273b934989..edc8ad0ac156 100644 --- a/common/machine_id.c +++ b/common/machine_id.c @@ -13,17 +13,96 @@ #define MACHINE_ID_LENGTH 32 +static bool __machine_id_initialized; static void *__machine_id_hashable; static size_t __machine_id_hashable_length; - +/** + * machine_id_set_hashable - Provide per-board unique data + * @hashable: Buffer + * @len: size of buffer + * + * The data supplied to the last call of this function prior to + * late_initcall will be hashed and stored into global.machine_id, + * which can be later used for fixup into the kernel command line + * or for deriving application specific unique IDs via + * machine_id_get_app_specific(). + */ void machine_id_set_hashable(const void *hashable, size_t len) { - __machine_id_hashable = xmemdup(hashable, len); __machine_id_hashable_length = len; } +/** + * machine_id_get_app_specific - Generates an application-specific UUID + * @result: UUID output of the function + * @...: pairs of (const void *, size_t) arguments of data to factor + * into the UUID followed by a NULL sentinel value. + * + * Combines the machine ID with the application specific varargs data + * to arrive at an application-specific and board-specific UUID that is + * stable and unique. + * + * The function returns 0 if a UUID was successfully written into @result + * and a negative error code otherwise. + */ +int machine_id_get_app_specific(uuid_t *result, ...) +{ + static u8 hmac[SHA256_DIGEST_SIZE]; + const void *data; + size_t size; + va_list args; + struct digest *d; + int ret; + + if (!__machine_id_initialized) + return -ENODATA; + + d = digest_alloc("hmac(sha256)"); + if (!d) + return -ENOSYS; + + ret = digest_set_key(d, __machine_id_hashable, __machine_id_hashable_length); + if (ret) + goto out; + + ret = digest_init(d); + if (ret) + goto out; + + ret = -ENODATA; + + va_start(args, result); + + while ((data = va_arg(args, const void *))) { + size = va_arg(args, size_t); + + ret = digest_update(d, data, size); + if (ret) + break; + } + + va_end(args); + + if (ret) + goto out; + + ret = digest_final(d, hmac); + if (ret) + goto out; + + /* Take only the first half. */ + memcpy(result, hmac, min(sizeof(hmac), sizeof(*result))); + + uuid_make_v4(result); + +out: + digest_free(d); + + return ret; +} + static int machine_id_set_globalvar(void) { struct digest *digest = NULL; @@ -61,6 +140,7 @@ static int machine_id_set_globalvar(void) env_machine_id = basprintf("%.*s", MACHINE_ID_LENGTH, hex_machine_id); globalvar_add_simple("machine_id", env_machine_id); free(env_machine_id); + __machine_id_initialized = true; out: digest_free(digest); diff --git a/include/linux/uuid.h b/include/linux/uuid.h index 6b1a3efa1e0b..1e4ffb343452 100644 --- a/include/linux/uuid.h +++ b/include/linux/uuid.h @@ -107,6 +107,14 @@ extern const u8 uuid_index[16]; int guid_parse(const char *uuid, guid_t *u); int uuid_parse(const char *uuid, uuid_t *u); +static inline void uuid_make_v4(uuid_t *u) { + /* Set UUID version to 4 --- truly random generation */ + u->b[6] = (u->b[6] & 0x0F) | 0x40; + + /* Set the UUID variant to DCE */ + u->b[8] = (u->b[8] & 0x3F) | 0x80; +} + /* MEI UUID type, don't use anywhere else */ #include <uapi/linux/uuid.h> diff --git a/include/machine_id.h b/include/machine_id.h index e30bbada1acd..0ed4052ec47c 100644 --- a/include/machine_id.h +++ b/include/machine_id.h @@ -3,9 +3,13 @@ #ifndef __MACHINE_ID_H__ #define __MACHINE_ID_H__ +#include <linux/types.h> +#include <linux/uuid.h> + #if IS_ENABLED(CONFIG_MACHINE_ID) void machine_id_set_hashable(const void *hashable, size_t len); +int machine_id_get_app_specific(uuid_t *result, ...) __attribute__((__sentinel__)); #else @@ -13,6 +17,12 @@ static inline void machine_id_set_hashable(const void *hashable, size_t len) { } +static inline int machine_id_get_app_specific(uuid_t *result, ...) + __attribute__((__sentinel__)); +{ + return -ENOSYS; +} + #endif /* CONFIG_MACHINE_ID */ #endif /* __MACHINE_ID_H__ */ -- 2.39.2
