libssh2: add CURLOPT_SSH_HOSTKEYFUNCTION

The callback set by CURLOPT_SSH_HOSTKEYFUNCTION is called to check
wether or not the connection should continue.

The host key is passed in argument with a custom handle for the
application.

It overrides CURLOPT_SSH_KNOWNHOSTS

Closes #7959

4 files changed, 91 insertions, 17 deletions

diff --git a/lib/easyoptions.c b/lib/easyoptions.c
index 04871ad1e..9ae6c6845 100644
--- a/lib/easyoptions.c
+++ b/lib/easyoptions.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             ___|___/|_| ______|
  *
- * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel.se>, et al.
+ * Copyright (C) 1998 - 2022, Daniel Stenberg, <daniel.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -279,6 +279,8 @@ struct curl_easyoption Curl_easyopts[] = {
    CURLOT_STRING, 0},
   {"SSH_KEYDATA", CURLOPT_SSH_KEYDATA, CURLOT_CBPTR, 0},
   {"SSH_KEYFUNCTION", CURLOPT_SSH_KEYFUNCTION, CURLOT_FUNCTION, 0},
+  {"SSH_HOSTKEYDATA", CURLOPT_SSH_HOSTKEYDATA, CURLOT_CBPTR, 0},
+  {"SSH_HOSTKEYFUNCTION", CURLOPT_SSH_HOSTKEYFUNCTION, CURLOT_FUNCTION, 0},
   {"SSH_KNOWNHOSTS", CURLOPT_SSH_KNOWNHOSTS, CURLOT_STRING, 0},
   {"SSH_PRIVATE_KEYFILE", CURLOPT_SSH_PRIVATE_KEYFILE, CURLOT_STRING, 0},
   {"SSH_PUBLIC_KEYFILE", CURLOPT_SSH_PUBLIC_KEYFILE, CURLOT_STRING, 0},
@@ -360,6 +362,6 @@ struct curl_easyoption Curl_easyopts[] = {
  */
 int Curl_easyopts_check(void)
 {
-  return ((CURLOPT_LASTENTRY%10000) != (315 + 1));
+  return ((CURLOPT_LASTENTRY%10000) != (317 + 1));
 }
 #endif
diff --git a/lib/setopt.c b/lib/setopt.c
index 19201393f..7dd9b5756 100644
--- a/lib/setopt.c
+++ b/lib/setopt.c
@@ -2466,7 +2466,19 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option, va_list param)
     result = Curl_setstropt(&data->set.str[STRING_SSH_KNOWNHOSTS],
                             va_arg(param, char *));
     break;
+#ifdef USE_LIBSSH2
+  case CURLOPT_SSH_HOSTKEYFUNCTION:
+    /* the callback to check the hostkey without the knownhost file */
+    data->set.ssh_hostkeyfunc = va_arg(param, curl_sshhostkeycallback);
+    break;
 
+  case CURLOPT_SSH_HOSTKEYDATA:
+    /*
+     * Custom client data to pass to the SSH keyfunc callback
+     */
+    data->set.ssh_hostkeyfunc_userp = va_arg(param, void *);
+    break;
+#endif
   case CURLOPT_SSH_KEYFUNCTION:
     /* setting to NULL is fine since the ssh.c functions themselves will
        then revert to use the internal default */
diff --git a/lib/urldata.h b/lib/urldata.h
index a3cf56169..4e0d52266 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1758,6 +1758,11 @@ struct UserDefined {
   int ftp_create_missing_dirs; /* 1 - create directories that don't exist
                                   2 - the same but also allow MKD to fail once
                                */
+#ifdef USE_LIBSSH2
+  curl_sshhostkeycallback ssh_hostkeyfunc; /* hostkey check callback */
+  void *ssh_hostkeyfunc_userp;         /* custom pointer to callback */
+#endif
+
   curl_sshkeycallback ssh_keyfunc; /* key matching callback */
   void *ssh_keyfunc_userp;         /* custom pointer to callback */
 #ifndef CURL_DISABLE_NETRC
diff --git a/lib/vssh/libssh2.c b/lib/vssh/libssh2.c
index d26926386..803cd5542 100644
--- a/lib/vssh/libssh2.c
+++ b/lib/vssh/libssh2.c
@@ -437,9 +437,45 @@ static int sshkeycallback(struct Curl_easy *easy,
 #else
 #define session_startup(x,y) libssh2_session_startup(x, (int)y)
 #endif
+static int convert_ssh2_keytype(int sshkeytype)
+{
+  int keytype = CURLKHTYPE_UNKNOWN;
+  switch(sshkeytype) {
+  case LIBSSH2_HOSTKEY_TYPE_RSA:
+    keytype = CURLKHTYPE_RSA;
+    break;
+  case LIBSSH2_HOSTKEY_TYPE_DSS:
+    keytype = CURLKHTYPE_DSS;
+    break;
+#ifdef LIBSSH2_HOSTKEY_TYPE_ECDSA_256
+  case LIBSSH2_HOSTKEY_TYPE_ECDSA_256:
+    keytype = CURLKHTYPE_ECDSA;
+    break;
+#endif
+#ifdef LIBSSH2_HOSTKEY_TYPE_ECDSA_384
+  case LIBSSH2_HOSTKEY_TYPE_ECDSA_384:
+    keytype = CURLKHTYPE_ECDSA;
+    break;
+#endif
+#ifdef LIBSSH2_HOSTKEY_TYPE_ECDSA_521
+  case LIBSSH2_HOSTKEY_TYPE_ECDSA_521:
+    keytype = CURLKHTYPE_ECDSA;
+    break;
+#endif
+#ifdef LIBSSH2_HOSTKEY_TYPE_ED25519
+  case LIBSSH2_HOSTKEY_TYPE_ED25519:
+    keytype = CURLKHTYPE_ED25519;
+    break;
+#endif
+  }
+  return keytype;
+}
 
 static CURLcode ssh_knownhost(struct Curl_easy *data)
 {
+  int sshkeytype = 0;
+  size_t keylen = 0;
+  int rc = 0;
   CURLcode result = CURLE_OK;
 
 #ifdef HAVE_LIBSSH2_KNOWNHOST_API
@@ -448,11 +484,8 @@ static CURLcode ssh_knownhost(struct Curl_easy *data)
     struct connectdata *conn = data->conn;
     struct ssh_conn *sshc = &conn->proto.sshc;
     struct libssh2_knownhost *host = NULL;
-    int rc;
-    int keytype;
-    size_t keylen;
     const char *remotekey = libssh2_session_hostkey(sshc->ssh_session,
-                                                    &keylen, &keytype);
+                                                    &keylen, &sshkeytype);
     int keycheck = LIBSSH2_KNOWNHOST_CHECK_FAILURE;
     int keybit = 0;
 
@@ -464,12 +497,12 @@ static CURLcode ssh_knownhost(struct Curl_easy *data)
        */
       enum curl_khmatch keymatch;
       curl_sshkeycallback func =
-        data->set.ssh_keyfunc?data->set.ssh_keyfunc:sshkeycallback;
+        data->set.ssh_keyfunc ? data->set.ssh_keyfunc : sshkeycallback;
       struct curl_khkey knownkey;
       struct curl_khkey *knownkeyp = NULL;
       struct curl_khkey foundkey;
 
-      switch(keytype) {
+      switch(sshkeytype) {
       case LIBSSH2_HOSTKEY_TYPE_RSA:
         keybit = LIBSSH2_KNOWNHOST_KEY_SSHRSA;
         break;
@@ -533,16 +566,14 @@ static CURLcode ssh_knownhost(struct Curl_easy *data)
         if(keycheck <= LIBSSH2_KNOWNHOST_CHECK_MISMATCH) {
           knownkey.key = host->key;
           knownkey.len = 0;
-          knownkey.keytype = (keytype == LIBSSH2_HOSTKEY_TYPE_RSA)?
-            CURLKHTYPE_RSA : CURLKHTYPE_DSS;
+          knownkey.keytype = convert_ssh2_keytype(sshkeytype);
           knownkeyp = &knownkey;
         }
 
         /* setup 'foundkey' */
         foundkey.key = remotekey;
         foundkey.len = keylen;
-        foundkey.keytype = (keytype == LIBSSH2_HOSTKEY_TYPE_RSA)?
-          CURLKHTYPE_RSA : CURLKHTYPE_DSS;
+        foundkey.keytype = convert_ssh2_keytype(sshkeytype);
 
         /*
          * if any of the LIBSSH2_KNOWNHOST_CHECK_* defines and the
@@ -639,7 +670,7 @@ static CURLcode ssh_check_fingerprint(struct Curl_easy *data)
 #ifdef LIBSSH2_HOSTKEY_HASH_SHA256
     /* The fingerprint points to static storage (!), don't free() it. */
     fingerprint = libssh2_hostkey_hash(sshc->ssh_session,
-        LIBSSH2_HOSTKEY_HASH_SHA256);
+                                       LIBSSH2_HOSTKEY_HASH_SHA256);
 #else
     const char *hostkey;
     size_t len = 0;
@@ -654,8 +685,8 @@ static CURLcode ssh_check_fingerprint(struct Curl_easy *data)
 
     if(!fingerprint) {
       failf(data,
-          "Denied establishing ssh session: sha256 fingerprint "
-          "not available");
+            "Denied establishing ssh session: sha256 fingerprint "
+            "not available");
       state(data, SSH_SESSION_FREE);
       sshc->actualcode = CURLE_PEER_FAILED_VERIFICATION;
       return sshc->actualcode;
@@ -715,7 +746,7 @@ static CURLcode ssh_check_fingerprint(struct Curl_easy *data)
     const char *fingerprint = NULL;
 
     fingerprint = libssh2_hostkey_hash(sshc->ssh_session,
-        LIBSSH2_HOSTKEY_HASH_MD5);
+                                       LIBSSH2_HOSTKEY_HASH_MD5);
 
     if(fingerprint) {
       /* The fingerprint points to static storage (!), don't free() it. */
@@ -748,7 +779,31 @@ static CURLcode ssh_check_fingerprint(struct Curl_easy *data)
   }
 
   if(!pubkey_md5 && !pubkey_sha256) {
-    return ssh_knownhost(data);
+    if(data->set.ssh_hostkeyfunc) {
+      size_t keylen = 0;
+      int sshkeytype = 0;
+      int rc = 0;
+      /* we handle the process to the callback*/
+      const char *remotekey = libssh2_session_hostkey(sshc->ssh_session,
+                                                      &keylen, &sshkeytype);
+      if(remotekey) {
+        int keytype = convert_ssh2_keytype(sshkeytype);
+        Curl_set_in_callback(data, true);
+        rc = data->set.ssh_hostkeyfunc(data->set.ssh_hostkeyfunc_userp,
+                                       keytype, remotekey, keylen);
+        Curl_set_in_callback(data, false);
+        if(rc!= CURLKHMATCH_OK) {
+          state(data, SSH_SESSION_FREE);
+        }
+      }
+      else {
+        state(data, SSH_SESSION_FREE);
+      }
+      return CURLE_OK;
+    }
+    else {
+      return ssh_knownhost(data);
+    }
   }
   else {
     /* as we already matched, we skip the check for known hosts */