From: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Date: Sat, 26 Aug 2023 10:34:34 +0000 (+0200)
Subject: sd-id128: avoid one memcpy
X-Git-Tag: v255-rc1~598^2~10
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0f7735d7a9232e04d40adb0a8604e62e69af57c2;p=thirdparty%2Fsystemd.git

sd-id128: avoid one memcpy

By aligning the output buffer, we can just use the result directly, no need to
copy stuff around.
---

diff --git a/src/libsystemd/sd-id128/sd-id128.c b/src/libsystemd/sd-id128/sd-id128.c
index 6a82a7f7b89..be6da9c88aa 100644
--- a/src/libsystemd/sd-id128/sd-id128.c
+++ b/src/libsystemd/sd-id128/sd-id128.c
@@ -339,17 +339,18 @@ _public_ int sd_id128_randomize(sd_id128_t *ret) {
 }
 
 static int get_app_specific(sd_id128_t base, sd_id128_t app_id, sd_id128_t *ret) {
-        uint8_t hmac[SHA256_DIGEST_SIZE];
-        sd_id128_t result;
+        assert_cc(sizeof(sd_id128_t) < SHA256_DIGEST_SIZE); /* Check that we don't need to pad with zeros. */
+        union {
+                uint8_t hmac[SHA256_DIGEST_SIZE];
+                sd_id128_t result;
+        } buf;
 
         assert(ret);
 
-        hmac_sha256(&base, sizeof(base), &app_id, sizeof(app_id), hmac);
+        hmac_sha256(&base, sizeof(base), &app_id, sizeof(app_id), buf.hmac);
 
         /* Take only the first half. */
-        memcpy(&result, hmac, MIN(sizeof(hmac), sizeof(result)));
-
-        *ret = id128_make_v4_uuid(result);
+        *ret = id128_make_v4_uuid(buf.result);
         return 0;
 }