- markus@cvs.openbsd.org 2002/05/23 19:24:30

     [authfile.c authfile.h pathnames.h ssh.c sshconnect.c sshconnect.h
      sshconnect1.c sshconnect2.c ssh-keysign.8 ssh-keysign.c Makefile.in]
     add /usr/libexec/ssh-keysign: a setuid helper program for hostbased
     authentication in protocol v2 (needs to access the hostkeys).

Note: Makefile.in untested.  Will test after merge is finished.

1 files changed, 204 insertions, 0 deletions

diff --git a/ssh-keysign.c b/ssh-keysign.c
new file mode 100644
index 000000000..da630708d
--- /dev/null
+++ b/ssh-keysign.c
@@ -0,0 +1,204 @@
+/*
+ * Copyright (c) 2002 Markus Friedl.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+#include "includes.h"
+RCSID("$OpenBSD: ssh-keysign.c,v 1.2 2002/05/31 10:30:33 markus Exp $");
+
+#include <openssl/evp.h>
+
+#include "log.h"
+#include "key.h"
+#include "ssh2.h"
+#include "misc.h"
+#include "xmalloc.h"
+#include "buffer.h"
+#include "bufaux.h"
+#include "authfile.h"
+#include "msg.h"
+#include "canohost.h"
+#include "pathnames.h"
+
+static int
+valid_request(struct passwd *pw, char *host, Key **ret, u_char *data,
+    u_int datalen)
+{
+        Buffer b;
+        Key *key;
+        u_char *pkblob;
+        u_int blen, len;
+        char *pkalg, *p;
+        int pktype, fail;
+
+        fail = 0;
+
+        buffer_init(&b);
+        buffer_append(&b, data, datalen);
+ 
+        /* session id */
+        buffer_skip_string(&b);
+        if (buffer_get_char(&b) != SSH2_MSG_USERAUTH_REQUEST)
+                fail++;
+
+        /* server user */
+        buffer_skip_string(&b);
+
+        /* service */
+        p = buffer_get_string(&b, NULL);
+        if (strcmp("ssh-connection", p) != 0)
+                fail++;
+        xfree(p);
+
+        /* method */
+        p = buffer_get_string(&b, NULL);
+        if (strcmp("hostbased", p) != 0)
+                fail++;
+        xfree(p);
+
+        /* pubkey */
+        pkalg = buffer_get_string(&b, NULL);
+        pkblob = buffer_get_string(&b, &blen);
+
+        pktype = key_type_from_name(pkalg);
+        if (pktype == KEY_UNSPEC)
+                fail++;
+        else if ((key = key_from_blob(pkblob, blen)) == NULL)
+                fail++;
+        else if (key->type != pktype)
+                fail++;
+        xfree(pkalg);
+        xfree(pkblob);
+
+        /* client host name, handle trailing dot */
+        p = buffer_get_string(&b, &len);
+        debug2("valid_request: check expect chost %s got %s", host, p);
+        if (strlen(host) != len - 1)
+                fail++;
+        else if (p[len - 1] != '.')
+              fail++;
+        else if (strncasecmp(host, p, len - 1) != 0)
+              fail++;
+        xfree(p);
+
+        /* local user */
+        p = buffer_get_string(&b, NULL);
+
+        if (strcmp(pw->pw_name, p) != 0)
+                fail++;
+        xfree(p);
+
+        /* end of message */
+        if (buffer_len(&b) != 0)
+                fail++;
+
+        debug3("valid_request: fail %d", fail);
+
+        if (fail && key != NULL)
+                key_free(key);
+        else
+                *ret = key;
+
+        return (fail ? -1 : 0);
+}
+
+int
+main(int argc, char **argv)
+{
+        Buffer b;
+        Key *keys[2], *key;
+        struct passwd *pw;
+        int key_fd[2], i, found, version = 2, fd;
+        u_char *signature, *data;
+        char *host;
+        u_int slen, dlen;
+
+        key_fd[0] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY);
+        key_fd[1] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY);
+
+        seteuid(getuid());
+        setuid(getuid());
+
+#ifdef DEBUG_SSH_KEYSIGN
+        log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0);
+#endif  
+
+        if (key_fd[0] == -1 && key_fd[1] == -1)
+                fatal("could not open any host key");
+
+        if ((pw = getpwuid(getuid())) == NULL)
+                fatal("getpwuid failed");
+        pw = pwcopy(pw); 
+
+        SSLeay_add_all_algorithms();
+
+        found = 0;
+        for (i = 0; i < 2; i++) {
+                keys[i] = NULL;
+                if (key_fd[i] == -1)
+                        continue;
+                keys[i] = key_load_private_pem(key_fd[i], KEY_UNSPEC,
+                    NULL, NULL);
+                close(key_fd[i]);
+                if (keys[i] != NULL)
+                        found = 1;
+        }
+        if (!found)
+                fatal("no hostkey found");
+
+        buffer_init(&b);
+        if (msg_recv(STDIN_FILENO, &b) < 0)
+                fatal("msg_recv failed");
+        if (buffer_get_char(&b) != version)
+                fatal("bad version");
+        fd = buffer_get_int(&b);
+        if ((fd == STDIN_FILENO) || (fd == STDOUT_FILENO))
+                fatal("bad fd");
+        if ((host = get_local_name(fd)) == NULL)
+                fatal("cannot get sockname for fd");
+        
+        data = buffer_get_string(&b, &dlen);
+        if (valid_request(pw, host, &key, data, dlen) < 0)
+                fatal("not a valid request");
+        xfree(data);
+        xfree(host);
+
+        found = 0;
+        for (i = 0; i < 2; i++) {
+                if (keys[i] != NULL &&
+                    key_equal(key, keys[i])) {
+                        found = 1;
+                        break;
+                }
+        }
+        if (!found)
+                fatal("no matching hostkey found");
+
+        if (key_sign(keys[i], &signature, &slen, data, dlen) != 0)
+                fatal("key_sign failed");
+        
+        /* send reply */
+        buffer_clear(&b);
+        buffer_put_string(&b, signature, slen);
+        msg_send(STDOUT_FILENO, version, &b);
+
+        return (0);
+}