File openssl-CVE-2016-0701.patch of Package openssl.4634
From: Matt Caswell <matt@openssl.org>
Date: Thu, 17 Dec 2015 02:57:20 +0000
Subject: Always generate DH keys for ephemeral DH cipher suites
Patch-mainline: OpenSSL_1_0_1r
Git-commit: 8bc643efc89cbcfba17369801cf4eeca037b6cc1
References: CVE-2016-0701 bsc#963413
Modified version of the commit ffaef3f15 in the master branch by Stephen
Henson. This makes the SSL_OP_SINGLE_DH_USE option a no-op and always
generates a new DH key for every handshake regardless.
This is a follow on from CVE-2016-0701. This branch is not impacted by
that CVE because it does not support X9.42 style parameters. It is still
possible to generate parameters based on primes that are not "safe",
although by default OpenSSL does not do this. The documentation does
sign post that using such parameters is unsafe if the private DH key is
reused. However to avoid accidental problems or future attacks this commit
has been backported to this branch.
Issue reported by Antonio Sanso
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
---
doc/ssl/SSL_CTX_set_tmp_dh_callback.pod | 29 +++++------------------------
ssl/s3_lib.c | 14 --------------
ssl/s3_srvr.c | 17 +++--------------
ssl/ssl.h | 2 +-
4 files changed, 9 insertions(+), 53 deletions(-)
diff --git a/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod b/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod
index b754c16a86e6..234fbc845002 100644
--- a/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod
+++ b/doc/ssl/SSL_CTX_set_tmp_dh_callback.pod
@@ -48,25 +48,8 @@ even if he gets hold of the normal (certified) key, as this key was
only used for signing.
In order to perform a DH key exchange the server must use a DH group
-(DH parameters) and generate a DH key.
-The server will always generate a new DH key during the negotiation
-if either the DH parameters are supplied via callback or the
-SSL_OP_SINGLE_DH_USE option of SSL_CTX_set_options(3) is set (or both).
-It will immediately create a DH key if DH parameters are supplied via
-SSL_CTX_set_tmp_dh() and SSL_OP_SINGLE_DH_USE is not set.
-In this case,
-it may happen that a key is generated on initialization without later
-being needed, while on the other hand the computer time during the
-negotiation is being saved.
-
-If "strong" primes were used to generate the DH parameters, it is not strictly
-necessary to generate a new key for each handshake but it does improve forward
-secrecy. If it is not assured that "strong" primes were used,
-SSL_OP_SINGLE_DH_USE must be used in order to prevent small subgroup
-attacks. Always using SSL_OP_SINGLE_DH_USE has an impact on the
-computer time needed during negotiation, but it is not very large, so
-application authors/users should consider always enabling this option.
-The option is required to implement perfect forward secrecy (PFS).
+(DH parameters) and generate a DH key. The server will always generate
+a new DH key during the negotiation.
As generating DH parameters is extremely time consuming, an application
should not generate the parameters on the fly but supply the parameters.
@@ -93,10 +76,9 @@ can supply the DH parameters via a callback function.
Previous versions of the callback used B<is_export> and B<keylength>
parameters to control parameter generation for export and non-export
cipher suites. Modern servers that do not support export ciphersuites
-are advised to either use SSL_CTX_set_tmp_dh() in combination with
-SSL_OP_SINGLE_DH_USE, or alternatively, use the callback but ignore
-B<keylength> and B<is_export> and simply supply at least 2048-bit
-parameters in the callback.
+are advised to either use SSL_CTX_set_tmp_dh() or alternatively, use
+the callback but ignore B<keylength> and B<is_export> and simply
+supply at least 2048-bit parameters in the callback.
=head1 EXAMPLES
@@ -128,7 +110,6 @@ partly left out.)
if (SSL_CTX_set_tmp_dh(ctx, dh_2048) != 1) {
/* Error. */
}
- SSL_CTX_set_options(ctx, SSL_OP_SINGLE_DH_USE);
...
=head1 RETURN VALUES
diff --git a/ssl/s3_lib.c b/ssl/s3_lib.c
index de917d3f836f..71bed58b6ec2 100644
--- a/ssl/s3_lib.c
+++ b/ssl/s3_lib.c
@@ -3164,13 +3164,6 @@ long ssl3_ctrl(SSL *s, int cmd, long larg, void *parg)
SSLerr(SSL_F_SSL3_CTRL, ERR_R_DH_LIB);
return (ret);
}
- if (!(s->options & SSL_OP_SINGLE_DH_USE)) {
- if (!DH_generate_key(dh)) {
- DH_free(dh);
- SSLerr(SSL_F_SSL3_CTRL, ERR_R_DH_LIB);
- return (ret);
- }
- }
if (s->cert->dh_tmp != NULL)
DH_free(s->cert->dh_tmp);
s->cert->dh_tmp = dh;
@@ -3479,13 +3472,6 @@ long ssl3_ctx_ctrl(SSL_CTX *ctx, int cmd, long larg, void *parg)
SSLerr(SSL_F_SSL3_CTX_CTRL, ERR_R_DH_LIB);
return 0;
}
- if (!(ctx->options & SSL_OP_SINGLE_DH_USE)) {
- if (!DH_generate_key(new)) {
- SSLerr(SSL_F_SSL3_CTX_CTRL, ERR_R_DH_LIB);
- DH_free(new);
- return 0;
- }
- }
if (cert->dh_tmp != NULL)
DH_free(cert->dh_tmp);
cert->dh_tmp = new;
diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c
index 3a5f71d745fa..5095b0462d44 100644
--- a/ssl/s3_srvr.c
+++ b/ssl/s3_srvr.c
@@ -1726,20 +1726,9 @@ int ssl3_send_server_key_exchange(SSL *s)
}
s->s3->tmp.dh = dh;
- if ((dhp->pub_key == NULL ||
- dhp->priv_key == NULL ||
- (s->options & SSL_OP_SINGLE_DH_USE))) {
- if (!DH_generate_key(dh)) {
- SSLerr(SSL_F_SSL3_SEND_SERVER_KEY_EXCHANGE, ERR_R_DH_LIB);
- goto err;
- }
- } else {
- dh->pub_key = BN_dup(dhp->pub_key);
- dh->priv_key = BN_dup(dhp->priv_key);
- if ((dh->pub_key == NULL) || (dh->priv_key == NULL)) {
- SSLerr(SSL_F_SSL3_SEND_SERVER_KEY_EXCHANGE, ERR_R_DH_LIB);
- goto err;
- }
+ if (!DH_generate_key(dh)) {
+ SSLerr(SSL_F_SSL3_SEND_SERVER_KEY_EXCHANGE, ERR_R_DH_LIB);
+ goto err;
}
r[0] = dh->p;
r[1] = dh->g;
diff --git a/ssl/ssl.h b/ssl/ssl.h
index d9657eb57495..ff07c92b14cf 100644
--- a/ssl/ssl.h
+++ b/ssl/ssl.h
@@ -602,7 +602,7 @@ struct ssl_session_st {
# define SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION 0x00040000L
/* If set, always create a new key when using tmp_ecdh parameters */
# define SSL_OP_SINGLE_ECDH_USE 0x00080000L
-/* If set, always create a new key when using tmp_dh parameters */
+/* Does nothing: retained for compatibility */
# define SSL_OP_SINGLE_DH_USE 0x00100000L
/* Does nothing: retained for compatibiity */
# define SSL_OP_EPHEMERAL_RSA 0x0
--
2.7.2
