- Added CURLOPT_SSH_KNOWNHOSTS, CURLOPT_SSH_KEYFUNCTION, CURLOPT_SSH_KEYDATA.

They introduce known_host support for SSH keys to libcurl. See docs for
  details.

CHANGES

@@ -6,19 +6,26 @@
 
                                   Changelog
 
+Daniel Stenberg (23 Jul 2009)
+- Added CURLOPT_SSH_KNOWNHOSTS, CURLOPT_SSH_KEYFUNCTION, CURLOPT_SSH_KEYDATA.
+  They introduce known_host support for SSH keys to libcurl. See docs for
+  details. Note that this feature depends on a new enough libssh2 version, to
+  be supported in libssh2 1.2 and later (or current git repo at this time).
+
 Michal Marek (22 Jul 2009)
 - David Binderman found a memory and fd leak in lib/gtls.c:load_file()
-  (https://bugzilla.novell.com/523919). When looking at the code, I found
+  (https://bugzilla.novell.com/523919). When looking at the code, I found that
-  that also the ptr pointer can leak.
+  also the ptr pointer can leak.
+
 Kamil Dudka (20 Jul 2009)
-- Claes Jakobsson improved the support for client certificates handling
+- Claes Jakobsson improved the support for client certificates handling in
-  in NSS-powered libcurl. Now the client certificates can be selected
+  NSS-powered libcurl. Now the client certificates can be selected
   automatically by a NSS built-in hook. Additionally pre-login to all PKCS11
   slots is no more performed. It used to cause problems with HW tokens.
 
 - Fixed reference counting for NSS client certificates. Now the PEM reader
-  module should be always properly unloaded on Curl_nss_cleanup(). If the unload
+  module should be always properly unloaded on Curl_nss_cleanup(). If the
-  fails though, libcurl will try to reuse the already loaded instance.
+  unload fails though, libcurl will try to reuse the already loaded instance.
 
 Daniel Fandrich (15 Jul 2009)
 - Added nonblock.c to the non-automake makefiles (note that the dependencies

RELEASE-NOTES

@@ -10,6 +10,7 @@ Curl and libcurl 7.19.6
 This release includes the following changes:
 
  o CURLOPT_FTPPORT (and curl's -P/--ftpport) support port ranges
+ o Added CURLOPT_SSH_KNOWNHOSTS, CURLOPT_SSH_KEYFUNCTION, CURLOPT_SSH_KEYDATA
 
 This release includes the following bugfixes:
 
@@ -32,6 +33,7 @@ This release includes the following bugfixes:
  o curl -o - sends data to stdout using binary mode on windows
  o fixed the separators for "array" style string that CURLINFO_CERTINFO returns
  o auth problem over several hosts with re-used connection
+ o improved the support for client certificates in libcurl+NSS
  o fix leak in gtls code
 
 This release includes the following known bugs:

docs/libcurl/curl_easy_setopt.3

@@ -1743,6 +1743,44 @@ Pass a char * pointing to a file name for your private key. If not used,
 libcurl defaults to using \fB~/.ssh/id_dsa\fP.
 If the file is password-protected, set the password with \fICURLOPT_KEYPASSWD\fP.
 (Added in 7.16.1)
+.IP CURLOPT_SSH_KNOWNHOSTS
+Pass a pointer to a zero terminated string holding the file name of the
+known_host file to use.  The known_hosts file should use the OpenSSH file
+format as supported by libssh2. If this file is specified, libcurl will only
+accept connections with hosts that are known and present in that file, with a
+matching public key. Use \fICURLOPT_SSH_KEYFUNCTION\fP to alter the default
+behavior on host and key (mis)matching. (Added in 7.19.6)
+.IP CURLOPT_SSH_KEYFUNCTION
+Pass a pointer to a curl_sshkeycallback function. It gets called when the
+known_host matching has been done, to allow the application to act and decide
+for libcurl how to proceed. It gets passed the CURL handle, the key from the
+known_hosts file, the key from the remote site, info from libcurl on the
+matching status and a custom pointer (set with \fICURLOPT_SSH_KEYDATA\fP). It
+MUST return one of the following return codes to tell libcurl how to act:
+.RS
+.IP CURLKHSTAT_FINE_ADD_TO_FILE
+The host+key is accepted and libcurl will append it to the known_hosts file
+before continuing with the connection. This will also add the host+key combo
+to the known_host pool kept in memory if it wasn't already present there. Note
+that the adding of data to the file is done by completely replacing the file
+with a new copy, so the permissions of the file must allow this.
+.IP CURLKHSTAT_FINE
+The host+key is accepted libcurl will continue with the connection. This will
+also add the host+key combo to the known_host pool kept in memory if it wasn't
+already present there.
+.IP CURLKHSTAT_REJECT
+The host+key is rejected. libcurl will deny the connection to continue and it
+will be closed.
+.IP CURLKHSTAT_DEFER
+The host+key is rejected, but the SSH connection is asked to be kept alive.
+This feature could be used when the app wants to somehow return back and act
+on the host+key situation and then retry without needing the overhead of
+setting it up from scratch again.
+.RE
+ (Added in 7.19.6)
+.IP CURLOPT_SSH_KEYDATA
+Pass a void * as parameter. This pointer will be passed along verbatim to the
+callback set with \fICURLOPT_SSH_KEYFUNCTION\fP. (Added in 7.19.6)
 .SH OTHER OPTIONS
 .IP CURLOPT_PRIVATE
 Pass a void * as parameter, pointing to data that should be associated with

include/curl/curl.h

@@ -493,6 +493,45 @@ typedef enum {
 
 #define CURL_ERROR_SIZE 256
 
+struct curl_khkey {
+  const char *key; /* points to a zero-terminated string encoded with base64
+                      if len is zero, otherwise to the "raw" data */
+  size_t len;
+  enum type {
+    CURLKHTYPE_UNKNOWN,
+    CURLKHTYPE_RSA1,
+    CURLKHTYPE_RSA,
+    CURLKHTYPE_DSS
+  } keytype;
+};
+
+/* this is the set of return values expected from the curl_sshkeycallback
+   callback */
+enum curl_khstat {
+  CURLKHSTAT_FINE_ADD_TO_FILE,
+  CURLKHSTAT_FINE,
+  CURLKHSTAT_REJECT, /* reject the connection, return an error */
+  CURLKHSTAT_DEFER,  /* do not accept it, but we can't answer right now so
+                        this causes a CURLE_DEFER error but otherwise the
+                        connection will be left intact etc */
+  CURLKHSTAT_LAST    /* not for use, only a marker for last-in-list */
+};
+
+/* this is the set of status codes pass in to the callback */
+enum curl_khmatch {
+  CURLKHMATCH_OK,       /* match */
+  CURLKHMATCH_MISMATCH, /* host found, key mismatch! */
+  CURLKHMATCH_MISSING,  /* no matching host/key found */
+  CURLKHMATCH_LAST      /* not for use, only a marker for last-in-list */
+};
+
+typedef int
+  (*curl_sshkeycallback) (CURL *easy,     /* easy handle */
+                          const struct curl_khkey *knownkey, /* known */
+                          const struct curl_khkey *foundkey, /* found */
+                          enum curl_khmatch, /* libcurl's view on the keys */
+                          void *clientp); /* custom pointer passed from app */
+
 /* parameter for the CURLOPT_USE_SSL option */
 typedef enum {
   CURLUSESSL_NONE,    /* do not attempt to use SSL */
@@ -1214,6 +1253,16 @@ typedef enum {
      to all protocols except FILE and SCP. */
   CINIT(REDIR_PROTOCOLS, LONG, 182),
 
+  /* set the SSH knownhost file name to use */
+  CINIT(SSH_KNOWNHOSTS, OBJECTPOINT, 183),
+
+  /* set the SSH host key callback, must point to a curl_sshkeycallback
+     function */
+  CINIT(SSH_KEYFUNCTION, FUNCTIONPOINT, 184),
+
+  /* set the SSH host key callback custom pointer */
+  CINIT(SSH_KEYDATA, OBJECTPOINT, 185),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;
 

lib/ssh.c

@@ -306,6 +306,7 @@ static void state(struct connectdata *conn, sshstate nowstate)
   static const char * const names[] = {
     "SSH_STOP",
     "SSH_S_STARTUP",
+    "SSH_HOSTKEY",
     "SSH_AUTHLIST",
     "SSH_AUTH_PKEY_INIT",
     "SSH_AUTH_PKEY",
@@ -433,6 +434,21 @@ static CURLcode ssh_getworkingpath(struct connectdata *conn,
   return CURLE_OK;
 }
 
+static int sshkeycallback(CURL *easy,
+                          const struct curl_khkey *knownkey, /* known */
+                          const struct curl_khkey *foundkey, /* found */
+                          enum curl_khmatch match,
+                          void *clientp)
+{
+  (void)easy;
+  (void)knownkey;
+  (void)foundkey;
+  (void)clientp;
+
+  /* we only allow perfect matches, and we reject everything else */
+  return (match != CURLKHMATCH_OK)?CURLKHSTAT_REJECT:CURLKHSTAT_FINE;
+}
+
 /*
  * Earlier libssh2 versions didn't have the ability to seek to 64bit positions
  * with 32bit size_t.
@@ -483,9 +499,15 @@ static CURLcode ssh_statemach_act(struct connectdata *conn, bool *block)
       break;
     }
 
-    /* Set libssh2 to non-blocking, since cURL is all non-blocking */
+    /* Set libssh2 to non-blocking, since everything internally is
+       non-blocking */
     libssh2_session_set_blocking(sshc->ssh_session, 0);
 
+    state(conn, SSH_HOSTKEY);
+
+    /* fall-through */
+  case SSH_HOSTKEY:
+
 #ifdef CURL_LIBSSH2_DEBUG
     /*
      * Before we authenticate we should check the hostkey's fingerprint
@@ -527,12 +549,121 @@ static CURLcode ssh_statemach_act(struct connectdata *conn, bool *block)
       }
     }
 
+#ifdef HAVE_LIBSSH2_KNOWNHOST_API
+    if(data->set.str[STRING_SSH_KNOWNHOSTS]) {
+      /* we're asked to verify the host against a file */
+      int keytype;
+      size_t keylen;
+      const char *remotekey = libssh2_session_hostkey(sshc->ssh_session,
+                                                      &keylen, &keytype);
+      int keycheck;
+      int keybit;
+
+      if(remotekey) {
+        /*
+         * A subject to figure out is what host name we need to pass in here.
+         * What host name does OpenSSH store in its file if an IDN name is
+         * used?
+         */
+        struct libssh2_knownhost *host;
+        enum curl_khmatch keymatch;
+        curl_sshkeycallback func =
+          data->set.ssh_keyfunc?data->set.ssh_keyfunc:sshkeycallback;
+        struct curl_khkey knownkey;
+        struct curl_khkey *knownkeyp = NULL;
+        struct curl_khkey foundkey;
+
+        keybit = (keytype == LIBSSH2_HOSTKEY_TYPE_RSA)?
+          LIBSSH2_KNOWNHOST_KEY_SSHRSA:LIBSSH2_KNOWNHOST_KEY_SSHDSS;
+
+        keycheck = libssh2_knownhost_check(sshc->kh,
+                                           conn->host.name,
+                                           remotekey, keylen,
+                                           LIBSSH2_KNOWNHOST_TYPE_PLAIN|
+                                           LIBSSH2_KNOWNHOST_KEYENC_RAW|
+                                           keybit,
+                                           &host);
+
+        infof(data, "SSH host check: %d, key: %s\n", keycheck,
+              (keycheck <= LIBSSH2_KNOWNHOST_CHECK_MISMATCH)?
+              host->key:"<none>");
+
+        /* setup 'knownkey' */
+        if(keycheck <= LIBSSH2_KNOWNHOST_CHECK_MISMATCH) {
+          knownkey.key = host->key;
+          knownkey.len = 0;
+          knownkey.keytype = (keytype == LIBSSH2_HOSTKEY_TYPE_RSA)?
+            CURLKHTYPE_RSA : CURLKHTYPE_DSS;
+          knownkeyp = &knownkey;
+        }
+
+        /* setup 'foundkey' */
+        foundkey.key = remotekey;
+        foundkey.len = keylen;
+        foundkey.keytype = (keytype == LIBSSH2_HOSTKEY_TYPE_RSA)?
+          CURLKHTYPE_RSA : CURLKHTYPE_DSS;
+
+        /*
+         * if any of the LIBSSH2_KNOWNHOST_CHECK_* defines and the
+         * curl_khmatch enum are ever modified, we need to introduce a
+         * translation table here!
+         */
+        keymatch = (enum curl_khmatch)keycheck;
+
+        /* Ask the callback how to behave */
+        rc = func(data, knownkeyp, /* from the knownhosts file */
+                  &foundkey, /* from the remote host */
+                  keymatch, data->set.ssh_keyfunc_userp);
+      }
+      else
+        /* no remotekey means failure! */
+        rc = CURLKHSTAT_REJECT;
+
+      switch(rc) {
+      default: /* unknown return codes will equal reject */
+      case CURLKHSTAT_REJECT:
+        state(conn, SSH_SESSION_FREE);
+      case CURLKHSTAT_DEFER:
+        /* DEFER means bail out but keep the SSH_HOSTKEY state */
+        result = sshc->actualcode = CURLE_PEER_FAILED_VERIFICATION;
+        break;
+      case CURLKHSTAT_FINE:
+      case CURLKHSTAT_FINE_ADD_TO_FILE:
+        /* proceed */
+        if(keycheck != LIBSSH2_KNOWNHOST_CHECK_MATCH) {
+          /* the found host+key didn't match but has been told to be fine
+             anyway so we add it in memory */
+          int addrc = libssh2_knownhost_add(sshc->kh,
+                                            conn->host.name, NULL,
+                                            remotekey, keylen,
+                                            LIBSSH2_KNOWNHOST_TYPE_PLAIN|
+                                            LIBSSH2_KNOWNHOST_KEYENC_RAW|
+                                            keybit, NULL);
+          if(addrc)
+            infof(data, "Warning adding the known host %s failed!\n",
+                  conn->host.name);
+          else if(rc == CURLKHSTAT_FINE_ADD_TO_FILE) {
+            /* now we write the entire in-memory list of known hosts to the
+               known_hosts file */
+            int wrc =
+              libssh2_knownhost_writefile(sshc->kh,
+                                          data->set.str[STRING_SSH_KNOWNHOSTS],
+                                          LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+            if(wrc) {
+              infof(data, "Warning, writing %s failed!\n",
+                    data->set.str[STRING_SSH_KNOWNHOSTS]);
+            }
+          }
+        }
+        break;
+      }
+    }
+#endif /* HAVE_LIBSSH2_KNOWNHOST_API */
+
     state(conn, SSH_AUTHLIST);
     break;
 
   case SSH_AUTHLIST:
-    /* TBD - methods to check the host keys need to be done */
-
     /*
      * Figure out authentication methods
      * NB: As soon as we have provided a username to an openssh server we
@@ -2278,6 +2409,26 @@ static CURLcode ssh_connect(struct connectdata *conn, bool *done)
     return CURLE_FAILED_INIT;
   }
 
+#ifdef HAVE_LIBSSH2_KNOWNHOST_API
+  if(data->set.str[STRING_SSH_KNOWNHOSTS]) {
+    int rc;
+    ssh->kh = libssh2_knownhost_init(ssh->ssh_session);
+    if(!ssh->kh) {
+      /* eeek. TODO: free the ssh_session! */
+      return CURLE_FAILED_INIT;
+    }
+
+    /* read all known hosts from there */
+    rc = libssh2_knownhost_readfile(ssh->kh,
+                                    data->set.str[STRING_SSH_KNOWNHOSTS],
+                                    LIBSSH2_KNOWNHOST_FILE_OPENSSH);
+    if(rc) {
+      infof(data, "Failed to read known hosts from %s\n",
+            data->set.str[STRING_SSH_KNOWNHOSTS]);
+    }
+  }
+#endif /* HAVE_LIBSSH2_KNOWNHOST_API */
+
 #ifdef CURL_LIBSSH2_DEBUG
   libssh2_trace(ssh->ssh_session, ~0);
   infof(data, "SSH socket: %d\n", sock);

lib/strerror.c

@@ -172,7 +172,7 @@ curl_easy_strerror(CURLcode error)
     return "Malformed telnet option";
 
   case CURLE_PEER_FAILED_VERIFICATION:
-    return "SSL peer certificate or SSH md5 fingerprint was not OK";
+    return "SSL peer certificate or SSH remote key was not OK";
 
   case CURLE_GOT_NOTHING:
     return "Server returned nothing (no headers, no data)";

lib/url.c

@@ -2169,6 +2169,8 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
     data->set.ssl.sessionid = (bool)(0 != va_arg(param, long));
     break;
 
+#ifdef USE_LIBSSH2
+    /* we only include SSH options if explicitly built to support SSH */
   case CURLOPT_SSH_AUTH_TYPES:
     data->set.ssh_auth_types = va_arg(param, long);
     break;
@@ -2196,6 +2198,31 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
     result = setstropt(&data->set.str[STRING_SSH_HOST_PUBLIC_KEY_MD5],
                        va_arg(param, char *));
     break;
+#ifdef HAVE_LIBSSH2_KNOWNHOST_API
+  case CURLOPT_SSH_KNOWNHOSTS:
+    /*
+     * Store the file name to read known hosts from.
+     */
+    result = setstropt(&data->set.str[STRING_SSH_KNOWNHOSTS],
+                       va_arg(param, char *));
+    break;
+
+  case CURLOPT_SSH_KEYFUNCTION:
+    /* setting to NULL is fine since the ssh.c functions themselves will
+       then rever to use the internal default */
+    data->set.ssh_keyfunc = va_arg(param, curl_sshkeycallback);
+    break;
+
+  case CURLOPT_SSH_KEYDATA:
+    /*
+     * Custom client data to pass to the SSH keyfunc callback
+     */
+    data->set.ssh_keyfunc_userp = va_arg(param, void *);
+    break;
+#endif /* HAVE_LIBSSH2_KNOWNHOST_API */
+
+#endif /* USE_LIBSSH2 */
+
   case CURLOPT_HTTP_TRANSFER_DECODING:
     /*
      * disable libcurl transfer encoding is used

lib/urldata.h

@@ -468,6 +468,7 @@ typedef enum {
   SSH_STOP = 0,       /* do nothing state, stops the state machine */
 
   SSH_S_STARTUP,      /* Session startup, First state in SSH-CONNECT */
+  SSH_HOSTKEY,        /* verify hostkey */
   SSH_AUTHLIST,
   SSH_AUTH_PKEY_INIT,
   SSH_AUTH_PKEY,
@@ -566,6 +567,12 @@ struct ssh_conn {
   LIBSSH2_SFTP_HANDLE *sftp_handle;
   int waitfor;                  /* current READ/WRITE bits to wait for */
   int orig_waitfor;             /* default READ/WRITE bits wait for */
+
+  /* note that HAVE_LIBSSH2_KNOWNHOST_API is a define set in the libssh2.h
+     header */
+#ifdef HAVE_LIBSSH2_KNOWNHOST_API
+  LIBSSH2_KNOWNHOSTS *kh;
+#endif
 #endif /* USE_LIBSSH2 */
 };
 
@@ -1366,15 +1373,12 @@ enum dupstring {
   STRING_SET_RANGE,       /* range, if used */
   STRING_SET_REFERER,     /* custom string for the HTTP referer field */
   STRING_SET_URL,         /* what original URL to work on */
-  STRING_SSH_PRIVATE_KEY, /* path to the private key file for auth */
-  STRING_SSH_PUBLIC_KEY,  /* path to the public key file for auth */
   STRING_SSL_CAPATH,      /* CA directory name (doesn't work on windows) */
   STRING_SSL_CAFILE,      /* certificate file to verify peer against */
   STRING_SSL_CIPHER_LIST, /* list of ciphers to use */
   STRING_SSL_EGDSOCKET,   /* path to file containing the EGD daemon socket */
   STRING_SSL_RANDOM_FILE, /* path to file containing "random" data */
   STRING_USERAGENT,       /* User-Agent string */
-  STRING_SSH_HOST_PUBLIC_KEY_MD5, /* md5 of host public key in ascii hex */
   STRING_SSL_CRLFILE,     /* crl file to check certificate */
   STRING_SSL_ISSUERCERT,  /* issuer cert file to check certificate */
   STRING_USERNAME,        /* <username>, if used */
@@ -1383,6 +1387,12 @@ enum dupstring {
   STRING_PROXYPASSWORD,   /* Proxy <password>, if used */
   STRING_NOPROXY,         /* List of hosts which should not use the proxy, if
                              used */
+#ifdef USE_LIBSSH2
+  STRING_SSH_PRIVATE_KEY, /* path to the private key file for auth */
+  STRING_SSH_PUBLIC_KEY,  /* path to the public key file for auth */
+  STRING_SSH_HOST_PUBLIC_KEY_MD5, /* md5 of host public key in ascii hex */
+  STRING_SSH_KNOWNHOSTS,  /* file name of knownhosts file */
+#endif
 #if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI)
   STRING_SOCKS5_GSSAPI_SERVICE,  /* GSSAPI service name */
 #endif
@@ -1496,6 +1506,9 @@ struct UserDefined {
                                   2 - the same but also allow MKD to fail once
                                */
 
+  curl_sshkeycallback ssh_keyfunc; /* key matching callback */
+  void *ssh_keyfunc_userp;         /* custom pointer to callback */
+
 /* Here follows boolean settings that define how to behave during
    this session. They are STATIC, set by libcurl users or at least initially
    and they don't change during operations. */

src/main.c

@@ -4694,6 +4694,16 @@ operate(struct Configurable *config, int argc, argv_item_t argv[])
           my_setopt(curl, CURLOPT_SSL_VERIFYPEER, FALSE);
           my_setopt(curl, CURLOPT_SSL_VERIFYHOST, 1);
         }
+        else {
+          char *home = homedir();
+          char *file = aprintf("%s/%sssh/known_hosts", home, DOT_CHAR);
+          if(home && file) {
+            free(home);
+            my_setopt_str(curl, CURLOPT_SSH_KNOWNHOSTS, file);
+          }
+          else
+            return CURLE_OUT_OF_MEMORY;
+        }
 
         if(config->no_body || config->remote_time) {
           /* no body or use remote time */