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Detect and deny excess renegotiations attempts.

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Switch 'server_handshake_count' from a uint8_t to 2 unsigned int bits.
Since we won't ever be doing more than 3 handshakes, we don't need the
extra space.

Toggle tor_tls_t.got_renegotiate based on the server_handshake_count.
Also assert that when we've done two handshakes as a server (the initial
SSL handshake, and the renegotiation handshake) we've just
renegotiated.

Finally, in tor_tls_read() return an error if we see more than 2
handshakes.
This commit is contained in:
George Kadianakis 2011-10-26 03:12:18 +02:00
parent 4fd79f9def
commit ecd239e3b5
1 changed files with 15 additions and 5 deletions
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20
src/common/tortls.c
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@ -146,7 +146,7 @@ struct tor_tls_t {
/** True iff we should call negotiated_callback when we're done reading. */
unsigned int got_renegotiate:1;
/** Incremented every time we start the server side of a handshake. */
uint8_t server_handshake_count;
unsigned int server_handshake_count:2;
size_t wantwrite_n; /**< 0 normally, >0 if we returned wantwrite last
* time. */
/** Last values retrieved from BIO_number_read()/write(); see
@ -1286,12 +1286,14 @@ tor_tls_client_is_using_v2_ciphers(const SSL *ssl, const char *address)
static void
tor_tls_got_server_hello(tor_tls_t *tls)
{
/* Check whether we're watching for renegotiates. If so, this is one! */
if (tls->negotiated_callback)
tls->got_renegotiate = 1;
if (tls->server_handshake_count < 127) /*avoid any overflow possibility*/
if (tls->server_handshake_count < 3)
++tls->server_handshake_count;
if (tls->server_handshake_count == 2) {
tor_assert(tls->negotiated_callback);
tls->got_renegotiate = 1;
}
/* Now check the cipher list. */
if (tor_tls_client_is_using_v2_ciphers(tls->ssl, ADDR(tls))) {
/*XXXX_TLS keep this from happening more than once! */
@ -1625,6 +1627,14 @@ tor_tls_read(tor_tls_t *tls, char *cp, size_t len)
tls->got_renegotiate = 0;
return r;
} else if (tls->server_handshake_count > 2) {
/* If we get more than 2 handshakes, it means that our peer is
trying to re-renegotiate. Return an error. */
tor_assert(tls->server_handshake_count == 3);
log_info(LD_NET, "Detected excess renegotiation from %s!", ADDR(tls));
return TOR_TLS_ERROR_MISC;
}
#endif