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From 56e0f123dc17cb99f50efbae4bbbab77f360818f Mon Sep 17 00:00:00 2001
From: Matt Caswell <matt@openssl.org>
Date: Mon, 3 Dec 2018 18:14:57 +0000
Subject: [PATCH] Revert "Reduce stack usage in tls13_hkdf_expand"
This reverts commit ec0c5f5693e39c5a013f81e6dd9dfd09ec65162d.
SSL_export_keying_material() may use longer label lengths.
Fixes #7712
Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7755)
(cherry picked from commit ed371b8cbac0d0349667558c061c1ae380cf75eb)
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
---
ssl/tls13_enc.c | 16 ++++------------
1 file changed, 4 insertions(+), 12 deletions(-)
diff --git a/ssl/tls13_enc.c b/ssl/tls13_enc.c
index b6825d20c2..f7ab0fa470 100644
--- a/ssl/tls13_enc.c
+++ b/ssl/tls13_enc.c
@@ -13,14 +13,7 @@
#include <openssl/evp.h>
#include <openssl/kdf.h>
-/*
- * RFC 8446, 7.1 Key Schedule, says:
- * Note: With common hash functions, any label longer than 12 characters
- * requires an additional iteration of the hash function to compute.
- * The labels in this specification have all been chosen to fit within
- * this limit.
- */
-#define TLS13_MAX_LABEL_LEN 12
+#define TLS13_MAX_LABEL_LEN 246
/* Always filled with zeros */
static const unsigned char default_zeros[EVP_MAX_MD_SIZE];
@@ -36,15 +29,14 @@ int tls13_hkdf_expand(SSL *s, const EVP_MD *md, const unsigned char *secret,
const unsigned char *data, size_t datalen,
unsigned char *out, size_t outlen)
{
- static const unsigned char label_prefix[] = "tls13 ";
+ const unsigned char label_prefix[] = "tls13 ";
EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_HKDF, NULL);
int ret;
size_t hkdflabellen;
size_t hashlen;
/*
- * 2 bytes for length of derived secret + 1 byte for length of combined
- * prefix and label + bytes for the label itself + 1 byte length of hash
- * + bytes for the hash itself
+ * 2 bytes for length of whole HkdfLabel + 1 byte for length of combined
+ * prefix and label + bytes for the label itself + bytes for the hash
*/
unsigned char hkdflabel[sizeof(uint16_t) + sizeof(uint8_t) +
+ sizeof(label_prefix) + TLS13_MAX_LABEL_LEN
--
2.20.1
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