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MINOR: acl: add support for TLS server name matching using SNI
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
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82a04566ec
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b6672b547a
@ -7598,6 +7598,12 @@ during analysis. This requires that some data has been buffered, for instance
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through TCP request content inspection. Please see the "tcp-request content"
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keyword for more detailed information on the subject.
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rep_ssl_hello_type <integer>
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Returns true when data in the response buffer looks like a complete SSL (v3
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or superior) hello message and handshake type is equal to <integer>.
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This test was designed to be used with TCP response content inspection: a
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SSL session ID may be fetched.
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req_len <integer>
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Returns true when the length of the data in the request buffer matches the
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specified range. It is important to understand that this test does not
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@ -7633,6 +7639,29 @@ req_rdp_cookie_cnt(<name>) <integer>
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of detecting the RDP protocol, as clients generally send the MSTS or MSTSHASH
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cookies.
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req_ssl_hello_type <integer>
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Returns true when data in the request buffer looks like a complete SSL (v3
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or superior) hello message and handshake type is equal to <integer>.
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This test was designed to be used with TCP request content inspection: an
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SSL session ID may be fetched.
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req_ssl_sni <string>
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Returns true when data in the request buffer looks like a complete SSL (v3
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or superior) client hello message with a Server Name Indication TLS extension
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(SNI) matching <string>. SNI normally contains the name of the host the
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client tries to connect to (for recent browsers). SNI is useful for allowing
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or denying access to certain hosts when SSL/TLS is used by the client. This
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test was designed to be used with TCP request content inspection. If content
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switching is needed, it is recommended to first wait for a complete client
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hello (type 1), like in the example below.
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Examples :
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# Wait for a client hello for at most 5 seconds
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tcp-request inspect-delay 5s
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tcp-request content accept if { req_ssl_hello_type 1 }
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use_backend bk_allow if { req_ssl_sni -f allowed_sites }
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default_backend bk_sorry_page
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req_ssl_ver <decimal>
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Returns true when data in the request buffer look like SSL, with a protocol
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version matching the specified range. Both SSLv2 hello messages and SSLv3
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@ -7642,18 +7671,6 @@ req_ssl_ver <decimal>
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that TLSv1 is announced as SSL version 3.1. This test was designed to be used
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with TCP request content inspection.
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req_ssl_hello_type <integer>
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Returns true when data in the request buffer looks like a complete SSL (v3
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or superior) hello message and handshake type is equal to <integer>.
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This test was designed to be used with TCP request content inspection: an
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SSL session ID may be fetched.
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rep_ssl_hello_type <integer>
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Returns true when data in the response buffer looks like a complete SSL (v3
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or superior) hello message and handshake type is equal to <integer>.
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This test was designed to be used with TCP response content inspection: a
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SSL session ID may be fetched.
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wait_end
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Waits for the end of the analysis period to return true. This may be used in
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conjunction with content analysis to avoid returning a wrong verdict early.
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170
src/acl.c
170
src/acl.c
@ -278,6 +278,175 @@ acl_fetch_req_ssl_ver(struct proxy *px, struct session *l4, void *l7, int dir,
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return 0;
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}
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/* Try to extract the Server Name Indication that may be presented in a TLS
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* client hello handshake message. The format of the message is the following
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* (cf RFC5246 + RFC6066) :
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* TLS frame :
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* - uint8 type = 0x16 (Handshake)
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* - uint16 version >= 0x0301 (TLSv1)
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* - uint16 length (frame length)
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* - TLS handshake :
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* - uint8 msg_type = 0x01 (ClientHello)
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* - uint24 length (handshake message length)
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* - ClientHello :
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* - uint16 client_version >= 0x0301 (TLSv1)
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* - uint8 Random[32]
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* - SessionID :
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* - uint8 session_id_len (0..32) (SessionID len in bytes)
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* - uint8 session_id[session_id_len]
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* - CipherSuite :
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* - uint16 cipher_len >= 2 (Cipher length in bytes)
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* - uint16 ciphers[cipher_len/2]
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* - CompressionMethod :
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* - uint8 compression_len >= 1 (# of supported methods)
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* - uint8 compression_methods[compression_len]
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* - optional client_extension_len (in bytes)
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* - optional sequence of ClientHelloExtensions (as many bytes as above):
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* - uint16 extension_type = 0 for server_name
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* - uint16 extension_len
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* - opaque extension_data[extension_len]
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* - uint16 server_name_list_len (# of bytes here)
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* - opaque server_names[server_name_list_len bytes]
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* - uint8 name_type = 0 for host_name
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* - uint16 name_len
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* - opaque hostname[name_len bytes]
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*/
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static int
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acl_fetch_ssl_hello_sni(struct proxy *px, struct session *l4, void *l7, int dir,
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struct acl_expr *expr, struct acl_test *test)
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{
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int hs_len, ext_len, bleft;
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struct buffer *b;
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unsigned char *data;
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if (!l4)
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goto not_ssl_hello;
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b = ((dir & ACL_DIR_MASK) == ACL_DIR_RTR) ? l4->rep : l4->req;
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bleft = b->l;
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data = (unsigned char *)b->w;
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/* Check for SSL/TLS Handshake */
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if (!bleft)
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goto too_short;
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if (*data != 0x16)
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goto not_ssl_hello;
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/* Check for TLSv1 or later (SSL version >= 3.1) */
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if (bleft < 3)
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goto too_short;
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if (data[1] < 0x03 || data[2] < 0x01)
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goto not_ssl_hello;
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if (bleft < 5)
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goto too_short;
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hs_len = (data[3] << 8) + data[4];
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if (hs_len < 1 + 3 + 2 + 32 + 1 + 2 + 2 + 1 + 1 + 2 + 2)
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goto not_ssl_hello; /* too short to have an extension */
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data += 5; /* enter TLS handshake */
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bleft -= 5;
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/* Check for a complete client hello starting at <data> */
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if (bleft < 1)
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goto too_short;
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if (data[0] != 0x01) /* msg_type = Client Hello */
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goto not_ssl_hello;
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/* Check the Hello's length */
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if (bleft < 4)
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goto too_short;
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hs_len = (data[1] << 16) + (data[2] << 8) + data[3];
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if (hs_len < 2 + 32 + 1 + 2 + 2 + 1 + 1 + 2 + 2)
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goto not_ssl_hello; /* too short to have an extension */
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/* We want the full handshake here */
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if (bleft < hs_len)
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goto too_short;
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data += 4;
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/* Start of the ClientHello message */
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if (data[0] < 0x03 || data[1] < 0x01) /* TLSv1 minimum */
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goto not_ssl_hello;
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ext_len = data[35];
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if (ext_len > 32 || ext_len > (hs_len - 35)) /* check for correct session_id len */
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goto not_ssl_hello;
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/* Jump to cipher suite */
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hs_len -= 35 + ext_len;
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data += 35 + ext_len;
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if (hs_len < 4 || /* minimum one cipher */
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(ext_len = (data[0] << 8) + data[1]) < 2 || /* minimum 2 bytes for a cipher */
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ext_len > hs_len)
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goto not_ssl_hello;
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/* Jump to the compression methods */
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hs_len -= 2 + ext_len;
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data += 2 + ext_len;
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if (hs_len < 2 || /* minimum one compression method */
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data[0] < 1 || data[0] > hs_len) /* minimum 1 bytes for a method */
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goto not_ssl_hello;
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/* Jump to the extensions */
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hs_len -= 1 + data[0];
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data += 1 + data[0];
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if (hs_len < 2 || /* minimum one extension list length */
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(ext_len = (data[0] << 8) + data[1]) > hs_len - 2) /* list too long */
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goto not_ssl_hello;
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hs_len = ext_len; /* limit ourselves to the extension length */
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data += 2;
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while (hs_len >= 4) {
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int ext_type, name_type, srv_len, name_len;
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ext_type = (data[0] << 8) + data[1];
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ext_len = (data[2] << 8) + data[3];
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if (ext_len > hs_len - 4) /* Extension too long */
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goto not_ssl_hello;
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if (ext_type == 0) { /* Server name */
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if (ext_len < 2) /* need one list length */
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goto not_ssl_hello;
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srv_len = (data[4] << 8) + data[5];
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if (srv_len < 4 || srv_len > hs_len - 6)
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goto not_ssl_hello; /* at least 4 bytes per server name */
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name_type = data[6];
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name_len = (data[7] << 8) + data[8];
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if (name_type == 0) { /* hostname */
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test->ptr = data + 9;
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test->len = name_len;
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test->flags = ACL_TEST_F_VOLATILE;
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//fprintf(stderr, "found SNI : <");
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//write(2, test->ptr, test->len);
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//fprintf(stderr, ">\n");
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return 1;
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}
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}
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hs_len -= 4 + ext_len;
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data += 4 + ext_len;
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}
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/* server name not found */
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goto not_ssl_hello;
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too_short:
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test->flags = ACL_TEST_F_MAY_CHANGE;
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not_ssl_hello:
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return 0;
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}
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/* Fetch the RDP cookie identified in the expression.
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* Note: this decoder only works with non-wrapping data.
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*/
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@ -1884,6 +2053,7 @@ static struct acl_kw_list acl_kws = {{ },{
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{ "req_ssl_ver", acl_parse_dotted_ver, acl_fetch_req_ssl_ver, acl_match_int, ACL_USE_L6REQ_VOLATILE },
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{ "req_rdp_cookie", acl_parse_str, acl_fetch_rdp_cookie, acl_match_str, ACL_USE_L6REQ_VOLATILE|ACL_MAY_LOOKUP },
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{ "req_rdp_cookie_cnt", acl_parse_int, acl_fetch_rdp_cookie_cnt, acl_match_int, ACL_USE_L6REQ_VOLATILE },
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{ "req_ssl_sni", acl_parse_str, acl_fetch_ssl_hello_sni, acl_match_str, ACL_USE_L6REQ_VOLATILE|ACL_MAY_LOOKUP },
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#if 0
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{ "time", acl_parse_time, acl_fetch_time, acl_match_time },
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#endif
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