ecki commented on code in PR #446:
URL: https://github.com/apache/mina-sshd/pull/446#discussion_r1435258249
##########
sshd-core/src/main/java/org/apache/sshd/common/session/helpers/AbstractSession.java:
##########
@@ -1741,6 +1979,143 @@ protected byte[] sendKexInit(Map<KexProposalOption,
String> proposal) throws Exc
return data;
}
+ protected String adjustOutgoingKexProposalOption(
+ KexProposalOption option, String value, boolean debugEnabled) {
+ if (GenericUtils.isBlank(value)) {
+ return value; // can happen for language (e.g.)
+ }
+
+ if (option != KexProposalOption.ALGORITHMS) {
+ return value;
+ }
+
+ if (!CoreModuleProperties.USE_STRICT_KEX.getRequired(this)) {
+ return value;
+ }
+
+ /*
+ * According to
https://github.com/openssh/openssh-portable/blob/master/PROTOCOL - section 1.9
+ *
+ * These pseudo-algorithms are only valid in the initial
SSH2_MSG_KEXINIT and
+ * MUST be ignored if they are present in subsequent
SSH2_MSG_KEXINIT packets.
+ *
+ * Therefore, if this is not the 1st outgoing packet don't bother
appending
+ */
+ long outgoingCount = totalOutgingPacketsCount.get();
+ if (outgoingCount > 0L) {
+ if (debugEnabled) {
+ log.debug("adjustKexOutgoingProposalOption({})[{}] not first
outgoing packet ({}) for proposal={}",
+ this, option, outgoingCount, value);
+ }
+ return value;
+ }
+
+ /*
+ * According to
https://github.com/openssh/openssh-portable/blob/master/PROTOCOL - section 1.9
+ *
+ * The client may append "kex-strict-c-...@openssh.com" to its
kex_algorithms
+ * and the server may append "kex-strict-s-...@openssh.com"
+ *
+ */
+ String proposal = isServerSession()
+ ? KexExtensions.STRICT_KEX_SERVER_EXTENSION
+ : KexExtensions.STRICT_KEX_CLIENT_EXTENSION;
+ String adjusted = value + "," + proposal;
+ if (debugEnabled) {
+ log.debug("adjustOutgoingKexProposalOption({})[{}] adjusted={}",
this, option, adjusted);
+ }
+
+ return adjusted;
+ }
+
+ protected String preProcessIncomingKexProposalOption(
+ KexProposalOption option, String value, boolean debugEnabled) {
+ if (GenericUtils.isBlank(value)) {
+ return value; // can happen for language (e.g.)
+ }
+
+ if (option != KexProposalOption.ALGORITHMS) {
+ return value;
+ }
+
+ if (!CoreModuleProperties.USE_STRICT_KEX.getRequired(this)) {
+ return value;
+ }
+
+ String peerValue = isServerSession()
+ ? KexExtensions.STRICT_KEX_CLIENT_EXTENSION
+ : KexExtensions.STRICT_KEX_SERVER_EXTENSION;
+ if (!value.contains(peerValue)) {
+ return value;
+ }
+
+ // Just a bit of paranoia...
Review Comment:
When you check if the peer value is present you can also check that the own
(I.e. c instead of s for a client connection) is not present, because that
would not be allowed. RFC8303 (which is analogous to the strict kex) says “may
disconnect” in 2.2:
> Implementations MUST NOT send an incorrect indicator name for their role.
Implementations MAY disconnect if the counterparty sends an incorrect
indicator. If "ext-info-c" or "ext-info-s" ends up being negotiated as a key
exchange method, the parties MUST disconnect.
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