1 files changed, 347 insertions, 0 deletions
diff --git a/svr-authpubkey.c b/svr-authpubkey.c
new file mode 100644
index 0000000..3942bd5
--- /dev/null
+++ b/svr-authpubkey.c
@@ -0,0 +1,347 @@
+/*
+ * Dropbear - a SSH2 server
+ * 
+ * Copyright (c) 2002,2003 Matt Johnston
+ * All rights reserved.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE. */
+
+/* Process a pubkey auth request */
+
+#include "includes.h"
+#include "session.h"
+#include "dbutil.h"
+#include "buffer.h"
+#include "signkey.h"
+#include "auth.h"
+#include "ssh.h"
+#include "packet.h"
+#include "algo.h"
+
+#ifdef ENABLE_SVR_PUBKEY_AUTH
+
+#define MIN_AUTHKEYS_LINE 10 /* "ssh-rsa AB" - short but doesn't matter */
+#define MAX_AUTHKEYS_LINE 4200 /* max length of a line in authkeys */
+
+static int checkpubkey(unsigned char* algo, unsigned int algolen,
+		unsigned char* keyblob, unsigned int keybloblen);
+static int checkpubkeyperms();
+static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
+		unsigned char* keyblob, unsigned int keybloblen);
+static int checkfileperm(char * filename);
+
+/* process a pubkey auth request, sending success or failure message as
+ * appropriate */
+void svr_auth_pubkey() {
+
+	unsigned char testkey; /* whether we're just checking if a key is usable */
+	unsigned char* algo = NULL; /* pubkey algo */
+	unsigned int algolen;
+	unsigned char* keyblob = NULL;
+	unsigned int keybloblen;
+	buffer * signbuf = NULL;
+	sign_key * key = NULL;
+	char* fp = NULL;
+	int type = -1;
+
+	TRACE(("enter pubkeyauth"))
+
+	/* 0 indicates user just wants to check if key can be used, 1 is an
+	 * actual attempt*/
+	testkey = (buf_getbool(ses.payload) == 0);
+
+	algo = buf_getstring(ses.payload, &algolen);
+	keybloblen = buf_getint(ses.payload);
+	keyblob = buf_getptr(ses.payload, keybloblen);
+
+	/* check if the key is valid */
+	if (checkpubkey(algo, algolen, keyblob, keybloblen) == DROPBEAR_FAILURE) {
+		send_msg_userauth_failure(0, 0);
+		goto out;
+	}
+
+	/* let them know that the key is ok to use */
+	if (testkey) {
+		send_msg_userauth_pk_ok(algo, algolen, keyblob, keybloblen);
+		goto out;
+	}
+
+	/* now we can actually verify the signature */
+	
+	/* get the key */
+	key = new_sign_key();
+	type = DROPBEAR_SIGNKEY_ANY;
+	if (buf_get_pub_key(ses.payload, key, &type) == DROPBEAR_FAILURE) {
+		send_msg_userauth_failure(0, 1);
+		goto out;
+	}
+
+	/* create the data which has been signed - this a string containing
+	 * session_id, concatenated with the payload packet up to the signature */
+	signbuf = buf_new(ses.payload->pos + 4 + SHA1_HASH_SIZE);
+	buf_putstring(signbuf, ses.session_id, SHA1_HASH_SIZE);
+	buf_putbytes(signbuf, ses.payload->data, ses.payload->pos);
+	buf_setpos(signbuf, 0);
+
+	/* ... and finally verify the signature */
+	fp = sign_key_fingerprint(keyblob, keybloblen);
+	if (buf_verify(ses.payload, key, buf_getptr(signbuf, signbuf->len),
+				signbuf->len) == DROPBEAR_SUCCESS) {
+		dropbear_log(LOG_NOTICE,
+				"pubkey auth succeeded for '%s' with key %s from %s",
+				ses.authstate.printableuser, fp, svr_ses.addrstring);
+		send_msg_userauth_success();
+	} else {
+		dropbear_log(LOG_WARNING,
+				"pubkey auth bad signature for '%s' with key %s from %s",
+				ses.authstate.printableuser, fp, svr_ses.addrstring);
+		send_msg_userauth_failure(0, 1);
+	}
+	m_free(fp);
+
+out:
+	/* cleanup stuff */
+	if (signbuf) {
+		buf_free(signbuf);
+	}
+	if (algo) {
+		m_free(algo);
+	}
+	if (key) {
+		sign_key_free(key);
+		key = NULL;
+	}
+	TRACE(("leave pubkeyauth"))
+}
+
+/* Reply that the key is valid for auth, this is sent when the user sends
+ * a straight copy of their pubkey to test, to avoid having to perform
+ * expensive signing operations with a worthless key */
+static void send_msg_userauth_pk_ok(unsigned char* algo, unsigned int algolen,
+		unsigned char* keyblob, unsigned int keybloblen) {
+
+	TRACE(("enter send_msg_userauth_pk_ok"))
+	CHECKCLEARTOWRITE();
+
+	buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_PK_OK);
+	buf_putstring(ses.writepayload, algo, algolen);
+	buf_putstring(ses.writepayload, keyblob, keybloblen);
+
+	encrypt_packet();
+	TRACE(("leave send_msg_userauth_pk_ok"))
+
+}
+
+/* Checks whether a specified publickey (and associated algorithm) is an
+ * acceptable key for authentication */
+/* Returns DROPBEAR_SUCCESS if key is ok for auth, DROPBEAR_FAILURE otherwise */
+static int checkpubkey(unsigned char* algo, unsigned int algolen,
+		unsigned char* keyblob, unsigned int keybloblen) {
+
+	FILE * authfile = NULL;
+	char * filename = NULL;
+	int ret = DROPBEAR_FAILURE;
+	buffer * line = NULL;
+	unsigned int len, pos;
+	
+	TRACE(("enter checkpubkey"))
+
+	/* check that we can use the algo */
+	if (have_algo(algo, algolen, sshhostkey) == DROPBEAR_FAILURE) {
+		dropbear_log(LOG_WARNING,
+				"pubkey auth attempt with unknown algo for '%s' from %s",
+				ses.authstate.printableuser, svr_ses.addrstring);
+		goto out;
+	}
+
+	/* check file permissions, also whether file exists */
+	if (checkpubkeyperms() == DROPBEAR_FAILURE) {
+		TRACE(("bad authorized_keys permissions, or file doesn't exist"))
+		goto out;
+	}
+
+	/* we don't need to check pw and pw_dir for validity, since
+	 * its been done in checkpubkeyperms. */
+	len = strlen(ses.authstate.pw->pw_dir);
+	/* allocate max required pathname storage,
+	 * = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
+	filename = m_malloc(len + 22);
+	snprintf(filename, len + 22, "%s/.ssh/authorized_keys", 
+				ses.authstate.pw->pw_dir);
+
+	/* open the file */
+	authfile = fopen(filename, "r");
+	if (authfile == NULL) {
+		goto out;
+	}
+	TRACE(("checkpubkey: opened authorized_keys OK"))
+
+	line = buf_new(MAX_AUTHKEYS_LINE);
+
+	/* iterate through the lines */
+	do {
+
+		if (buf_getline(line, authfile) == DROPBEAR_FAILURE) {
+			/* EOF reached */
+			TRACE(("checkpubkey: authorized_keys EOF reached"))
+			break;
+		}
+
+		if (line->len < MIN_AUTHKEYS_LINE) {
+			TRACE(("checkpubkey: line too short"))
+			continue; /* line is too short for it to be a valid key */
+		}
+
+		/* check the key type - this also stops us from using keys
+		 * which have options with them */
+		if (strncmp(buf_getptr(line, algolen), algo, algolen) != 0) {
+			continue;
+		}
+		buf_incrpos(line, algolen);
+		
+		/* check for space (' ') character */
+		if (buf_getbyte(line) != ' ') {
+			TRACE(("checkpubkey: space character expected, isn't there"))
+			continue;
+		}
+
+		/* truncate the line at the space after the base64 data */
+		pos = line->pos;
+		for (len = 0; line->pos < line->len; len++) {
+			if (buf_getbyte(line) == ' ') break;
+		}	
+		buf_setpos(line, pos);
+		buf_setlen(line, line->pos + len);
+
+		TRACE(("checkpubkey: line pos = %d len = %d", line->pos, line->len))
+
+		ret = cmp_base64_key(keyblob, keybloblen, algo, algolen, line);
+		if (ret == DROPBEAR_SUCCESS) {
+			break;
+		}
+
+		/* We continue to the next line otherwise */
+		
+	} while (1);
+
+out:
+	if (authfile) {
+		fclose(authfile);
+	}
+	if (line) {
+		buf_free(line);
+	}
+	m_free(filename);
+	TRACE(("leave checkpubkey: ret=%d", ret))
+	return ret;
+}
+
+
+/* Returns DROPBEAR_SUCCESS if file permissions for pubkeys are ok,
+ * DROPBEAR_FAILURE otherwise.
+ * Checks that the user's homedir, ~/.ssh, and
+ * ~/.ssh/authorized_keys are all owned by either root or the user, and are
+ * g-w, o-w */
+static int checkpubkeyperms() {
+
+	char* filename = NULL; 
+	int ret = DROPBEAR_FAILURE;
+	unsigned int len;
+
+	TRACE(("enter checkpubkeyperms"))
+
+	if (ses.authstate.pw->pw_dir == NULL) {
+		goto out;
+	}
+
+	if ((len = strlen(ses.authstate.pw->pw_dir)) == 0) {
+		goto out;
+	}
+
+	/* allocate max required pathname storage,
+	 * = path + "/.ssh/authorized_keys" + '\0' = pathlen + 22 */
+	filename = m_malloc(len + 22);
+	strncpy(filename, ses.authstate.pw->pw_dir, len+1);
+
+	/* check ~ */
+	if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
+		goto out;
+	}
+
+	/* check ~/.ssh */
+	strncat(filename, "/.ssh", 5); /* strlen("/.ssh") == 5 */
+	if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
+		goto out;
+	}
+
+	/* now check ~/.ssh/authorized_keys */
+	strncat(filename, "/authorized_keys", 16);
+	if (checkfileperm(filename) != DROPBEAR_SUCCESS) {
+		goto out;
+	}
+
+	/* file looks ok, return success */
+	ret = DROPBEAR_SUCCESS;
+	
+out:
+	m_free(filename);
+
+	TRACE(("leave checkpubkeyperms"))
+	return ret;
+}
+
+/* Checks that a file is owned by the user or root, and isn't writable by
+ * group or other */
+/* returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
+static int checkfileperm(char * filename) {
+	struct stat filestat;
+	int badperm = 0;
+
+	TRACE(("enter checkfileperm(%s)", filename))
+
+	if (stat(filename, &filestat) != 0) {
+		TRACE(("leave checkfileperm: stat() != 0"))
+		return DROPBEAR_FAILURE;
+	}
+	/* check ownership - user or root only*/
+	if (filestat.st_uid != ses.authstate.pw->pw_uid
+			&& filestat.st_uid != 0) {
+		badperm = 1;
+		TRACE(("wrong ownership"))
+	}
+	/* check permissions - don't want group or others +w */
+	if (filestat.st_mode & (S_IWGRP | S_IWOTH)) {
+		badperm = 1;
+		TRACE(("wrong perms"))
+	}
+	if (badperm) {
+		if (!ses.authstate.perm_warn) {
+			ses.authstate.perm_warn = 1;
+			dropbear_log(LOG_INFO, "%s must be owned by user or root, and not writable by others", filename);
+		}
+		TRACE(("leave checkfileperm: failure perms/owner"))
+		return DROPBEAR_FAILURE;
+	}
+
+	TRACE(("leave checkfileperm: success"))
+	return DROPBEAR_SUCCESS;
+}
+
+
+#endif