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MINOR: acl: add support for TLS server name matching using SNI

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Server Name Indication (SNI) is a TLS extension which makes a client
present the name of the server it is connecting to in the client hello.
It allows a transparent proxy to take a decision based on the beginning
of an SSL/TLS stream without deciphering it.

The new ACL "req_ssl_sni" matches the name extracted from the TLS
handshake against a list of names which may be loaded from a file if
needed.
This commit is contained in:
Willy Tarreau 2011-12-12 17:23:41 +01:00
parent 82a04566ec
commit b6672b547a
2 changed files with 199 additions and 12 deletions
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41
doc/configuration.txt
View File

@ -7598,6 +7598,12 @@ during analysis. This requires that some data has been buffered, for instance
through TCP request content inspection. Please see the "tcp-request content"
keyword for more detailed information on the subject.
rep_ssl_hello_type <integer>
Returns true when data in the response buffer looks like a complete SSL (v3
or superior) hello message and handshake type is equal to <integer>.
This test was designed to be used with TCP response content inspection: a
SSL session ID may be fetched.
req_len <integer>
Returns true when the length of the data in the request buffer matches the
specified range. It is important to understand that this test does not
@ -7633,6 +7639,29 @@ req_rdp_cookie_cnt(<name>) <integer>
of detecting the RDP protocol, as clients generally send the MSTS or MSTSHASH
cookies.
req_ssl_hello_type <integer>
Returns true when data in the request buffer looks like a complete SSL (v3
or superior) hello message and handshake type is equal to <integer>.
This test was designed to be used with TCP request content inspection: an
SSL session ID may be fetched.
req_ssl_sni <string>
Returns true when data in the request buffer looks like a complete SSL (v3
or superior) client hello message with a Server Name Indication TLS extension
(SNI) matching <string>. SNI normally contains the name of the host the
client tries to connect to (for recent browsers). SNI is useful for allowing
or denying access to certain hosts when SSL/TLS is used by the client. This
test was designed to be used with TCP request content inspection. If content
switching is needed, it is recommended to first wait for a complete client
hello (type 1), like in the example below.
Examples :
# Wait for a client hello for at most 5 seconds
tcp-request inspect-delay 5s
tcp-request content accept if { req_ssl_hello_type 1 }
use_backend bk_allow if { req_ssl_sni -f allowed_sites }
default_backend bk_sorry_page
req_ssl_ver <decimal>
Returns true when data in the request buffer look like SSL, with a protocol
version matching the specified range. Both SSLv2 hello messages and SSLv3
@ -7642,18 +7671,6 @@ req_ssl_ver <decimal>
that TLSv1 is announced as SSL version 3.1. This test was designed to be used
with TCP request content inspection.
req_ssl_hello_type <integer>
Returns true when data in the request buffer looks like a complete SSL (v3
or superior) hello message and handshake type is equal to <integer>.
This test was designed to be used with TCP request content inspection: an
SSL session ID may be fetched.
rep_ssl_hello_type <integer>
Returns true when data in the response buffer looks like a complete SSL (v3
or superior) hello message and handshake type is equal to <integer>.
This test was designed to be used with TCP response content inspection: a
SSL session ID may be fetched.
wait_end
Waits for the end of the analysis period to return true. This may be used in
conjunction with content analysis to avoid returning a wrong verdict early.

170
src/acl.c
View File

@ -278,6 +278,175 @@ acl_fetch_req_ssl_ver(struct proxy *px, struct session *l4, void *l7, int dir,
return 0;
}
/* Try to extract the Server Name Indication that may be presented in a TLS
* client hello handshake message. The format of the message is the following
* (cf RFC5246 + RFC6066) :
* TLS frame :
* - uint8 type = 0x16 (Handshake)
* - uint16 version >= 0x0301 (TLSv1)
* - uint16 length (frame length)
* - TLS handshake :
* - uint8 msg_type = 0x01 (ClientHello)
* - uint24 length (handshake message length)
* - ClientHello :
* - uint16 client_version >= 0x0301 (TLSv1)
* - uint8 Random[32]
* - SessionID :
* - uint8 session_id_len (0..32) (SessionID len in bytes)
* - uint8 session_id[session_id_len]
* - CipherSuite :
* - uint16 cipher_len >= 2 (Cipher length in bytes)
* - uint16 ciphers[cipher_len/2]
* - CompressionMethod :
* - uint8 compression_len >= 1 (# of supported methods)
* - uint8 compression_methods[compression_len]
* - optional client_extension_len (in bytes)
* - optional sequence of ClientHelloExtensions (as many bytes as above):
* - uint16 extension_type = 0 for server_name
* - uint16 extension_len
* - opaque extension_data[extension_len]
* - uint16 server_name_list_len (# of bytes here)
* - opaque server_names[server_name_list_len bytes]
* - uint8 name_type = 0 for host_name
* - uint16 name_len
* - opaque hostname[name_len bytes]
*/
static int
acl_fetch_ssl_hello_sni(struct proxy *px, struct session *l4, void *l7, int dir,
struct acl_expr *expr, struct acl_test *test)
{
int hs_len, ext_len, bleft;
struct buffer *b;
unsigned char *data;
if (!l4)
goto not_ssl_hello;
b = ((dir & ACL_DIR_MASK) == ACL_DIR_RTR) ? l4->rep : l4->req;
bleft = b->l;
data = (unsigned char *)b->w;
/* Check for SSL/TLS Handshake */
if (!bleft)
goto too_short;
if (*data != 0x16)
goto not_ssl_hello;
/* Check for TLSv1 or later (SSL version >= 3.1) */
if (bleft < 3)
goto too_short;
if (data[1] < 0x03 || data[2] < 0x01)
goto not_ssl_hello;
if (bleft < 5)
goto too_short;
hs_len = (data[3] << 8) + data[4];
if (hs_len < 1 + 3 + 2 + 32 + 1 + 2 + 2 + 1 + 1 + 2 + 2)
goto not_ssl_hello; /* too short to have an extension */
data += 5; /* enter TLS handshake */
bleft -= 5;
/* Check for a complete client hello starting at <data> */
if (bleft < 1)
goto too_short;
if (data[0] != 0x01) /* msg_type = Client Hello */
goto not_ssl_hello;
/* Check the Hello's length */
if (bleft < 4)
goto too_short;
hs_len = (data[1] << 16) + (data[2] << 8) + data[3];
if (hs_len < 2 + 32 + 1 + 2 + 2 + 1 + 1 + 2 + 2)
goto not_ssl_hello; /* too short to have an extension */
/* We want the full handshake here */
if (bleft < hs_len)
goto too_short;
data += 4;
/* Start of the ClientHello message */
if (data[0] < 0x03 || data[1] < 0x01) /* TLSv1 minimum */
goto not_ssl_hello;
ext_len = data[35];
if (ext_len > 32 || ext_len > (hs_len - 35)) /* check for correct session_id len */
goto not_ssl_hello;
/* Jump to cipher suite */
hs_len -= 35 + ext_len;
data += 35 + ext_len;
if (hs_len < 4 || /* minimum one cipher */
(ext_len = (data[0] << 8) + data[1]) < 2 || /* minimum 2 bytes for a cipher */
ext_len > hs_len)
goto not_ssl_hello;
/* Jump to the compression methods */
hs_len -= 2 + ext_len;
data += 2 + ext_len;
if (hs_len < 2 || /* minimum one compression method */
data[0] < 1 || data[0] > hs_len) /* minimum 1 bytes for a method */
goto not_ssl_hello;
/* Jump to the extensions */
hs_len -= 1 + data[0];
data += 1 + data[0];
if (hs_len < 2 || /* minimum one extension list length */
(ext_len = (data[0] << 8) + data[1]) > hs_len - 2) /* list too long */
goto not_ssl_hello;
hs_len = ext_len; /* limit ourselves to the extension length */
data += 2;
while (hs_len >= 4) {
int ext_type, name_type, srv_len, name_len;
ext_type = (data[0] << 8) + data[1];
ext_len = (data[2] << 8) + data[3];
if (ext_len > hs_len - 4) /* Extension too long */
goto not_ssl_hello;
if (ext_type == 0) { /* Server name */
if (ext_len < 2) /* need one list length */
goto not_ssl_hello;
srv_len = (data[4] << 8) + data[5];
if (srv_len < 4 || srv_len > hs_len - 6)
goto not_ssl_hello; /* at least 4 bytes per server name */
name_type = data[6];
name_len = (data[7] << 8) + data[8];
if (name_type == 0) { /* hostname */
test->ptr = data + 9;
test->len = name_len;
test->flags = ACL_TEST_F_VOLATILE;
//fprintf(stderr, "found SNI : <");
//write(2, test->ptr, test->len);
//fprintf(stderr, ">\n");
return 1;
}
}
hs_len -= 4 + ext_len;
data += 4 + ext_len;
}
/* server name not found */
goto not_ssl_hello;
too_short:
test->flags = ACL_TEST_F_MAY_CHANGE;
not_ssl_hello:
return 0;
}
/* Fetch the RDP cookie identified in the expression.
* Note: this decoder only works with non-wrapping data.
*/
@ -1884,6 +2053,7 @@ static struct acl_kw_list acl_kws = {{ },{
{ "req_ssl_ver", acl_parse_dotted_ver, acl_fetch_req_ssl_ver, acl_match_int, ACL_USE_L6REQ_VOLATILE },
{ "req_rdp_cookie", acl_parse_str, acl_fetch_rdp_cookie, acl_match_str, ACL_USE_L6REQ_VOLATILE|ACL_MAY_LOOKUP },
{ "req_rdp_cookie_cnt", acl_parse_int, acl_fetch_rdp_cookie_cnt, acl_match_int, ACL_USE_L6REQ_VOLATILE },
{ "req_ssl_sni", acl_parse_str, acl_fetch_ssl_hello_sni, acl_match_str, ACL_USE_L6REQ_VOLATILE|ACL_MAY_LOOKUP },
#if 0
{ "time", acl_parse_time, acl_fetch_time, acl_match_time },
#endif