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server: Support for extension negotiation

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This includes intercepting the  ext-info-c  string from
the client kex proposal, configuring the server to allow using
this extension and sending the SSH_MSG_EXT_INFO packet back
to the client after the new keys are in use.

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
This commit is contained in:
Jakub Jelen
2018-07-03 16:16:25 +02:00
committed by Andreas Schneider
parent 60ad7ee15d
commit 6fa5e8adb0
3 changed files with 58 additions and 2 deletions
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41
src/server.c
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@@ -67,7 +67,6 @@
static int dh_handshake_server(ssh_session session);
/**
* @addtogroup libssh_server
*
@@ -194,6 +193,37 @@ static int ssh_server_kexdh_init(ssh_session session, ssh_buffer packet){
return SSH_OK;
}
static int ssh_server_send_extensions(ssh_session session) {
int rc;
const char *hostkey_algorithms;
SSH_LOG(SSH_LOG_PACKET, "Sending SSH_MSG_EXT_INFO");
/*
* We can list here all the default hostkey methods, since
* they already contain the SHA2 extension algorithms
*/
hostkey_algorithms = ssh_kex_get_default_methods(SSH_HOSTKEYS);
rc = ssh_buffer_pack(session->out_buffer,
"bdss",
SSH2_MSG_EXT_INFO,
1, /* nr. of extensions */
"server-sig-algs",
hostkey_algorithms);
if (rc != SSH_OK) {
goto error;
}
if (ssh_packet_send(session) == SSH_ERROR) {
goto error;
}
return 0;
error:
ssh_buffer_reinit(session->out_buffer);
return -1;
}
SSH_PACKET_CALLBACK(ssh_packet_kexdh_init){
int rc = SSH_ERROR;
(void)type;
@@ -486,6 +516,15 @@ static void ssh_server_connection_callback(ssh_session session){
session->session_state=SSH_SESSION_STATE_AUTHENTICATING;
if (session->flags & SSH_SESSION_FLAG_AUTHENTICATED)
session->session_state = SSH_SESSION_STATE_AUTHENTICATED;
/*
* If the client supports extension negotiation, we will send
* our supported extensions now. This is the first message after
* sending NEWKEYS message and after turning on crypto.
*/
if (session->extensions) {
ssh_server_send_extensions(session);
}
}
break;
case SSH_SESSION_STATE_AUTHENTICATING: