upstream: authfd: add function to check if key is in agent

This commit adds a helper function which allows the caller to
check if a given public key is present in ssh-agent.

work by Sebastian Kinne; ok markus@

OpenBSD-Commit-ID: d43c5826353e1fdc1af71eb42961b30782c7bd13

1 files changed, 27 insertions, 1 deletions

diff --git a/authfd.c b/authfd.c
index 315c6813f..a5162790f 100644
--- a/authfd.c
+++ b/authfd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: authfd.c,v 1.116 2019/09/03 08:28:30 djm Exp $ */
+/* $OpenBSD: authfd.c,v 1.117 2019/09/03 08:29:15 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -318,6 +318,32 @@ ssh_free_identitylist(struct ssh_identitylist *idl)
 }
 
 /*
+ * Check if the ssh agent has a given key.
+ * Returns 0 if found, or a negative SSH_ERR_* error code on failure.
+ */
+int
+ssh_agent_has_key(int sock, struct sshkey *key)
+{
+        int r, ret = SSH_ERR_KEY_NOT_FOUND;
+        size_t i;
+        struct ssh_identitylist *idlist = NULL;
+
+        if ((r = ssh_fetch_identitylist(sock, &idlist)) < 0) {
+                return r;
+        }
+
+        for (i = 0; i < idlist->nkeys; i++) {
+                if (sshkey_equal_public(idlist->keys[i], key)) {
+                        ret = 0;
+                        break;
+                }
+        }
+
+        ssh_free_identitylist(idlist);
+        return ret;
+}
+
+/*
  * Sends a challenge (typically from a server via ssh(1)) to the agent,
  * and waits for a response from the agent.
  * Returns true (non-zero) if the agent gave the correct answer, zero