Commit d3224bad authored by Nick Mathewson's avatar Nick Mathewson 🎨
Browse files

r14227@Kushana: nickm | 2007-08-27 11:33:28 -0400

 Add a new ClientDNSRejectInternalAddresses option (default: on) to refuse to believe that any address can map to or from an internal address.  This blocks some kinds of potential browser-based attacks, especially on hosts using DNSPort.  Also clarify behavior in some comments.  Backport candiate?


svn:r11287
parent 0608ec71
Changes in version 0.2.0.6-alpha - 2007-??-??
o Minor features (security):
- As a client, do not believe any server that tells us that any address
maps to an internal address space.
Changes in version 0.2.0.6-alpha - 2007-08-26
o New directory authorities:
- Set up Tonga as the default bridge directory authority.
......
......@@ -676,6 +676,13 @@ Bind to this address to listen for DNS connections.
(Default: 127.0.0.1).
.LP
.TP
\fBClientDNSRejectInternalAddresses\fP \fR\fB0\fR|\fB1\fR\fP
If true, Tor does not believe any anonymously retrieved DNS answer that tells
it that an address resolves to an internal address (like 127.0.0.1 or
192.168.0.1). This option prevents certain browser-based attacks; don't turn
it off unless you know what you're doing. (Default: 1).
.LP
.TP
\fBDownloadExtraInfo\fP \fR\fB0\fR|\fB1\fR\fP
If true, Tor downloads and caches "extra-info" documents. These
documents contain information about servers other than the information
......
......@@ -2601,7 +2601,9 @@ tor_addr_to_str(char *dest, const tor_addr_t *addr, int len)
}
/** Convert the string in <b>src</b> to a tor_addr_t <b>addr</b>.
*/
*
* Return an address family on success, or -1 if an invalid address string is
* provided. */
int
tor_addr_from_str(tor_addr_t *addr, const char *src)
{
......
......@@ -143,6 +143,8 @@ static config_var_t _option_vars[] = {
VAR("Bridge", LINELIST, Bridges, NULL),
VAR("CircuitBuildTimeout", INTERVAL, CircuitBuildTimeout, "1 minute"),
VAR("CircuitIdleTimeout", INTERVAL, CircuitIdleTimeout, "1 hour"),
VAR("ClientDNSRejectInternalAddresses", BOOL,
ClientDNSRejectInternalAddresses, "1"),
VAR("ClientOnly", BOOL, ClientOnly, "0"),
VAR("ConnLimit", UINT, ConnLimit, "1000"),
VAR("ConstrainedSockets", BOOL, ConstrainedSockets, "0"),
......@@ -827,7 +829,8 @@ options_act_reversible(or_options_t *old_options, char **msg)
int logs_marked = 0;
/* Daemonize _first_, since we only want to open most of this stuff in
* the subprocess. */
* the subprocess. Libevent bases can't be reliably inherited across
* processes. */
if (running_tor && options->RunAsDaemon) {
/* No need to roll back, since you can't change the value. */
start_daemon();
......
......@@ -1247,6 +1247,19 @@ connection_ap_handshake_rewrite_and_attach(edge_connection_t *conn,
END_STREAM_REASON_FLAG_ALREADY_SOCKS_REPLIED);
return 0;
}
if (options->ClientDNSRejectInternalAddresses) {
/* Don't let people try to do a reverse lookup on 10.0.0.1. */
tor_addr_t addr;
if (tor_addr_from_str(&addr, socks->address) >= 0 &&
tor_addr_is_internal(&addr, 0)) {
connection_ap_handshake_socks_resolved(conn, RESOLVED_TYPE_ERROR,
0, NULL, -1, TIME_MAX);
connection_mark_unattached_ap(conn,
END_STREAM_REASON_SOCKSPROTOCOL |
END_STREAM_REASON_FLAG_ALREADY_SOCKS_REPLIED);
return -1;
}
}
} else if (!automap) {
/* For address map controls, remap the address. */
if (addressmap_rewrite(socks->address, sizeof(socks->address),
......
......@@ -191,7 +191,8 @@
#define DEFAULT_DNS_TTL (30*60)
/** How long can a TTL be before we stop believing it? */
#define MAX_DNS_TTL (3*60*60)
/** How small can a TTL be before we stop believing it? */
/** How small can a TTL be before we stop believing it? Provides rudimentary
* pinning. */
#define MIN_DNS_TTL (60)
/** How often do we rotate onion keys? */
......@@ -2093,6 +2094,11 @@ typedef struct {
* if we are a cache). For authorities, this is always true. */
int DownloadExtraInfo;
/** If true, do not believe anybody who tells us that a domain resolves
* to an internal address, or that an internal address has a PTR mapping.
* Helps avoid some cross-site attacks. */
int ClientDNSRejectInternalAddresses;
/** The length of time that we think a consensus should be fresh. */
int V3AuthVotingInterval;
/** The length of time we think it will take to distribute votes */
......
......@@ -900,9 +900,14 @@ connection_edge_process_relay_cell_not_open(
if (rh->length >= 4) {
uint32_t addr = ntohl(get_uint32(cell->payload+RELAY_HEADER_SIZE));
int ttl;
if (!addr) {
if (!addr || (get_options()->ClientDNSRejectInternalAddresses &&
is_internal_IP(addr, 0))) {
char buf[INET_NTOA_BUF_LEN];
struct in_addr a;
a.s_addr = htonl(addr);
tor_inet_ntoa(&a, buf, sizeof(buf));
log_info(LD_APP,
"...but it claims the IP address was 0.0.0.0. Closing.");
"...but it claims the IP address was %s. Closing.", buf);
connection_edge_end(conn, END_STREAM_REASON_TORPROTOCOL);
connection_mark_unattached_ap(conn, END_STREAM_REASON_TORPROTOCOL);
return 0;
......@@ -946,13 +951,28 @@ connection_edge_process_relay_cell_not_open(
connection_mark_unattached_ap(conn, END_STREAM_REASON_TORPROTOCOL);
return 0;
}
answer_type = cell->payload[RELAY_HEADER_SIZE];
if (rh->length >= answer_len+6)
ttl = (int)ntohl(get_uint32(cell->payload+RELAY_HEADER_SIZE+
2+answer_len));
else
ttl = -1;
answer_type = cell->payload[RELAY_HEADER_SIZE];
if (answer_type == RESOLVED_TYPE_IPV4 && answer_len >= 4) {
uint32_t addr = ntohl(get_uint32(cell->payload+RELAY_HEADER_SIZE+2));
if (get_options()->ClientDNSRejectInternalAddresses &&
is_internal_IP(addr, 0)) {
char buf[INET_NTOA_BUF_LEN];
struct in_addr a;
a.s_addr = htonl(addr);
tor_inet_ntoa(&a, buf, sizeof(buf));
log_info(LD_APP,"Got a resolve with answer %s. Rejecting.", buf);
connection_ap_handshake_socks_resolved(conn,
RESOLVED_TYPE_ERROR_TRANSIENT,
0, NULL, 0, TIME_MAX);
connection_mark_unattached_ap(conn, END_STREAM_REASON_TORPROTOCOL);
return 0;
}
}
connection_ap_handshake_socks_resolved(conn,
answer_type,
cell->payload[RELAY_HEADER_SIZE+1], /*answer_len*/
......
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