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- /*
- * Data structure managing host keys in sessions based on GSSAPI KEX.
- *
- * In a session we started with a GSSAPI key exchange, the concept of
- * 'host key' has completely different lifetime and security semantics
- * from the usual ones. Per RFC 4462 section 2.1, we assume that any
- * host key delivered to us in the course of a GSSAPI key exchange is
- * _solely_ there to use as a transient fallback within the same
- * session, if at the time of a subsequent rekey the GSS credentials
- * are temporarily invalid and so a non-GSS KEX method has to be used.
- *
- * In particular, in a GSS-based SSH deployment, host keys may not
- * even _be_ persistent identities for the server; it would be
- * legitimate for a server to generate a fresh one routinely if it
- * wanted to, like SSH-1 server keys.
- *
- * So, in this mode, we never touch the persistent host key cache at
- * all, either to check keys against it _or_ to store keys in it.
- * Instead, we maintain an in-memory cache of host keys that have been
- * mentioned in GSS key exchanges within this particular session, and
- * we permit precisely those host keys in non-GSS rekeys.
- */
- #include <assert.h>
- #include "putty.h"
- #include "ssh.h"
- struct ssh_transient_hostkey_cache {
- tree234 *cache;
- };
- struct ssh_transient_hostkey_cache_entry {
- const ssh_keyalg *alg;
- strbuf *pub_blob;
- };
- static int ssh_transient_hostkey_cache_cmp(void *av, void *bv)
- {
- const struct ssh_transient_hostkey_cache_entry
- *a = (const struct ssh_transient_hostkey_cache_entry *)av,
- *b = (const struct ssh_transient_hostkey_cache_entry *)bv;
- return strcmp(a->alg->ssh_id, b->alg->ssh_id);
- }
- static int ssh_transient_hostkey_cache_find(void *av, void *bv)
- {
- const ssh_keyalg *aalg = (const ssh_keyalg *)av;
- const struct ssh_transient_hostkey_cache_entry
- *b = (const struct ssh_transient_hostkey_cache_entry *)bv;
- return strcmp(aalg->ssh_id, b->alg->ssh_id);
- }
- ssh_transient_hostkey_cache *ssh_transient_hostkey_cache_new(void)
- {
- ssh_transient_hostkey_cache *thc = snew(ssh_transient_hostkey_cache);
- thc->cache = newtree234(ssh_transient_hostkey_cache_cmp);
- return thc;
- }
- void ssh_transient_hostkey_cache_free(ssh_transient_hostkey_cache *thc)
- {
- struct ssh_transient_hostkey_cache_entry *ent;
- while ((ent = delpos234(thc->cache, 0)) != NULL) {
- strbuf_free(ent->pub_blob);
- sfree(ent);
- }
- freetree234(thc->cache);
- sfree(thc);
- }
- void ssh_transient_hostkey_cache_add(
- ssh_transient_hostkey_cache *thc, ssh_key *key)
- {
- struct ssh_transient_hostkey_cache_entry *ent, *retd;
- if ((ent = find234(thc->cache, (void *)ssh_key_alg(key),
- ssh_transient_hostkey_cache_find)) != NULL) {
- del234(thc->cache, ent);
- strbuf_free(ent->pub_blob);
- sfree(ent);
- }
- ent = snew(struct ssh_transient_hostkey_cache_entry);
- ent->alg = ssh_key_alg(key);
- ent->pub_blob = strbuf_new();
- ssh_key_public_blob(key, BinarySink_UPCAST(ent->pub_blob));
- retd = add234(thc->cache, ent);
- assert(retd == ent);
- }
- bool ssh_transient_hostkey_cache_verify(
- ssh_transient_hostkey_cache *thc, ssh_key *key)
- {
- struct ssh_transient_hostkey_cache_entry *ent;
- bool toret = false;
- if ((ent = find234(thc->cache, (void *)ssh_key_alg(key),
- ssh_transient_hostkey_cache_find)) != NULL) {
- strbuf *this_blob = strbuf_new();
- ssh_key_public_blob(key, BinarySink_UPCAST(this_blob));
- if (this_blob->len == ent->pub_blob->len &&
- !memcmp(this_blob->s, ent->pub_blob->s,
- this_blob->len))
- toret = true;
- strbuf_free(this_blob);
- }
- return toret;
- }
- bool ssh_transient_hostkey_cache_has(
- ssh_transient_hostkey_cache *thc, const ssh_keyalg *alg)
- {
- struct ssh_transient_hostkey_cache_entry *ent =
- find234(thc->cache, (void *)alg,
- ssh_transient_hostkey_cache_find);
- return ent != NULL;
- }
- bool ssh_transient_hostkey_cache_non_empty(ssh_transient_hostkey_cache *thc)
- {
- return count234(thc->cache) > 0;
- }
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