From: Luca Boccassi <luca.boccassi@gmail.com>
Date: Mon, 29 Jun 2026 13:01:08 +0000 (+0100)
Subject: fido2: reject zero-length HMAC secret
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=a3bf0f2f860ff9e73c9062d9f3c400bc672496ac;p=thirdparty%2Fsystemd.git

fido2: reject zero-length HMAC secret

The CTAP2 HMAC-SECRET output should never be zero length, so enforce
that at both retrieval sites.

Follow-up for 1c0c4a43c6118aa4057222789e4b777b61e4bb27
---

diff --git a/src/shared/libfido2-util.c b/src/shared/libfido2-util.c
index 4a0d7e6d647..07bea6658ec 100644
--- a/src/shared/libfido2-util.c
+++ b/src/shared/libfido2-util.c
@@ -622,6 +622,8 @@ static int fido2_use_hmac_hash_specific_token(
                 return log_error_errno(SYNTHETIC_ERRNO(EIO), "Failed to retrieve HMAC secret.");
 
         hmac_size = sym_fido_assert_hmac_secret_len(a, 0);
+        /* Should never be zero, sanity check */
+        assert(hmac_size > 0);
 
         hmac_copy = memdup(hmac, hmac_size);
         if (!hmac_copy)
@@ -1160,6 +1162,8 @@ int fido2_generate_hmac_hash(
                 return log_error_errno(SYNTHETIC_ERRNO(EIO), "Failed to retrieve HMAC secret.");
 
         secret_size = sym_fido_assert_hmac_secret_len(a, 0);
+        /* Should never be zero, sanity check */
+        assert(secret_size > 0);
 
         secret_copy = memdup(secret, secret_size);
         if (!secret_copy)