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MINOR: ssl: add prefer-client-ciphers

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Currently we unconditionally set SSL_OP_CIPHER_SERVER_PREFERENCE [1],
which may not always be a good thing.

The benefit of server side cipher prioritization may not apply to all
cases out there, and it appears that the various SSL libs are going away
from this recommendation ([2], [3]), as insecure ciphers suites are
properly blacklisted/removed and honoring the client's preference is
more likely to improve user experience  (for example using SW-friendly
ciphers on devices without HW AES support).

This is especially true for TLSv1.3, which will restrict the cipher
suites to just AES-GCM and Chacha20/Poly1305.

Apache [4], nginx [5] and others give admins full flexibility, we should
as well.

The initial proposal to change the current default and add a
"prefer-server-ciphers" option (as implemented in e566ecb) has been
declined due to the possible security impact.

This patch implements prefer-client-ciphers without changing the defaults.

[1] https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html
[2] https://github.com/openssl/openssl/issues/541
[3] https://github.com/libressl-portable/portable/issues/66
[4] https://httpd.apache.org/docs/2.0/en/mod/mod_ssl.html#sslhonorcipherorder
[5] https://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_prefer_server_ciphers
This commit is contained in:
Lukas Tribus 2017-05-04 15:45:40 +00:00 committed by Willy Tarreau
parent f494977bc1
commit 53ae85c38e
3 changed files with 18 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
doc/configuration.txt
View File

@ -10592,6 +10592,11 @@ npn <protocols>
enabled (check with haproxy -vv). Note that the NPN extension has been
replaced with the ALPN extension (see the "alpn" keyword).
prefer-client-ciphers
Use the client's preference when selecting the cipher suite, by default
the server's preference is enforced. This option is also available on
global statement "ssl-default-bind-options".
process [ all | odd | even | <number 1-64>[-<number 1-64>] ]
This restricts the list of processes on which this listener is allowed to
run. It does not enforce any process but eliminates those which do not match.

1
include/types/listener.h
View File

@ -114,6 +114,7 @@ enum li_state {
#define BC_SSL_O_USE_TLSV12 0x0080 /* force TLSv12 */
/* 0x00F0 reserved for 'force' protocol version options */
#define BC_SSL_O_NO_TLS_TICKETS 0x0100 /* disable session resumption tickets */
#define BC_SSL_O_PREF_CLIE_CIPH 0x0200 /* prefer client ciphers */
#endif
/* ssl "bind" settings */

12
src/ssl_sock.c
View File

@ -3238,6 +3238,8 @@ ssl_sock_initial_ctx(struct bind_conf *bind_conf)
}
if (conf_ssl_options & BC_SSL_O_NO_TLS_TICKETS)
ssloptions |= SSL_OP_NO_TICKET;
if (conf_ssl_options & BC_SSL_O_PREF_CLIE_CIPH)
ssloptions &= ~SSL_OP_CIPHER_SERVER_PREFERENCE;
SSL_CTX_set_options(ctx, ssloptions);
SSL_CTX_set_mode(ctx, sslmode);
if (global_ssl.life_time)
@ -6327,6 +6329,13 @@ static int bind_parse_ssl(char **args, int cur_arg, struct proxy *px, struct bin
return 0;
}
/* parse the "prefer-client-ciphers" bind keyword */
static int bind_parse_pcc(char **args, int cur_arg, struct proxy *px, struct bind_conf *conf, char **err)
{
conf->ssl_options |= BC_SSL_O_PREF_CLIE_CIPH;
return 0;
}
/* parse the "generate-certificates" bind keyword */
static int bind_parse_generate_certs(char **args, int cur_arg, struct proxy *px, struct bind_conf *conf, char **err)
{
@ -6870,6 +6879,8 @@ static int ssl_parse_default_bind_options(char **args, int section_type, struct
}
else if (!strcmp(args[i], "no-tls-tickets"))
global_ssl.listen_default_ssloptions |= BC_SSL_O_NO_TLS_TICKETS;
else if (!strcmp(args[i], "prefer-client-ciphers"))
global_ssl.listen_default_ssloptions |= BC_SSL_O_PREF_CLIE_CIPH;
else {
memprintf(err, "unknown option '%s' on global statement '%s'.", args[i], args[0]);
return -1;
@ -7505,6 +7516,7 @@ static struct bind_kw_list bind_kws = { "SSL", { }, {
{ "tls-ticket-keys", bind_parse_tls_ticket_keys, 1 }, /* set file to load TLS ticket keys from */
{ "verify", bind_parse_verify, 1 }, /* set SSL verify method */
{ "npn", bind_parse_npn, 1 }, /* set NPN supported protocols */
{ "prefer-client-ciphers", bind_parse_pcc, 0 }, /* prefer client ciphers */
{ NULL, NULL, 0 },
}};