From: Michael Brown <mcb30@ipxe.org>
Date: Wed, 8 Jul 2026 10:14:50 +0000 (+0100)
Subject: [tls] Poison initial key derivation function master secret
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=792849763633f62ff9cbeec4ea22939b53d1c2fa;p=thirdparty%2Fipxe.git

[tls] Poison initial key derivation function master secret

A freshly initialised key derivation function master secret has the
"keyed" flag clear and so cannot accidentally be used to establish a
full TLS connection.

As an additional layer of defence in depth, poison the initial key
derivation master secret so that a predictable all-zero secret can
never be used accidentally in future.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---

diff --git a/src/net/tls.c b/src/net/tls.c
index f0cad9ff0..9c2f4cdf6 100644
--- a/src/net/tls.c
+++ b/src/net/tls.c
@@ -549,6 +549,9 @@ static int tls_set_digest ( struct tls_connection *tls,
 	/* Initialise handshake context */
 	digest_init ( digest, key->handshake );
 
+	/* Poison key derivation function master secret */
+	tls_ephemeral_label ( tls, "kdf poison", key->kdf, kdfsize );
+
 	/* Sanity checks */
 	assert ( ! key->keyed );
 	assert ( ! key->bound );