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Correct and enhance the behaviour of "internal" session caching as it

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relates to SSL_CTX flags and the use of "external" session caching. The
existing flag, "SSL_SESS_CACHE_NO_INTERNAL_LOOKUP" remains but is
supplemented with a complimentary flag, "SSL_SESS_CACHE_NO_INTERNAL_STORE".
The bitwise OR of the two flags is also defined as
"SSL_SESS_CACHE_NO_INTERNAL" and is the flag that should be used by most
applications wanting to implement session caching *entirely* by its own
provided callbacks. As the documented behaviour contradicted actual
behaviour up until recently, and since that point behaviour has itself been
inconsistent anyway, this change should not introduce any compatibility
problems. I've adjusted the relevant documentation to elaborate about how
this works.

Kudos to "Nadav Har'El" <nyh@math.technion.ac.il> for diagnosing these
anomalies and testing this patch for correctness.

PR: 311
This commit is contained in:
Geoff Thorpe 2002-10-29 00:33:04 +00:00
parent 00a357ab20
commit e0db2eed8d
5 changed files with 54 additions and 19 deletions
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8
doc/ssl/SSL_CTX_add_session.pod
View File

@ -37,6 +37,14 @@ removed and replaced by the new session. If the session is actually
identical (the SSL_SESSION object is identical), SSL_CTX_add_session()
is a no-op, and the return value is 0.
If a server SSL_CTX is configured with the SSL_SESS_CACHE_NO_INTERNAL_STORE
flag then the internal cache will not be populated automatically by new
sessions negotiated by the SSL/TLS implementation, even though the internal
cache will be searched automatically for session-resume requests (the
latter can be surpressed by SSL_SESS_CACHE_NO_INTERNAL_LOOKUP). So the
application can use SSL_CTX_add_session() directly to have full control
over the sessions that can be resumed if desired.
=head1 RETURN VALUES

47
doc/ssl/SSL_CTX_set_session_cache_mode.pod
View File

@ -26,12 +26,14 @@ SSL_CTX object is being maintained, the sessions are unique for each SSL_CTX
object.
In order to reuse a session, a client must send the session's id to the
server. It can only send exactly one id. The server then decides whether it
agrees in reusing the session or starts the handshake for a new session.
server. It can only send exactly one id. The server then either
agrees to reuse the session or it starts a full handshake (to create a new
session).
A server will lookup up the session in its internal session storage. If
the session is not found in internal storage or internal storage is
deactivated, the server will try the external storage if available.
A server will lookup up the session in its internal session storage. If the
session is not found in internal storage or lookups for the internal storage
have been deactivated (SSL_SESS_CACHE_NO_INTERNAL_LOOKUP), the server will try
the external storage if available.
Since a client may try to reuse a session intended for use in a different
context, the session id context must be set by the server (see
@ -57,9 +59,10 @@ function. This option is not activated by default.
=item SSL_SESS_CACHE_SERVER
Server sessions are added to the session cache. When a client proposes a
session to be reused, the session is looked up in the internal session cache.
If the session is found, the server will try to reuse the session.
This is the default.
session to be reused, the server looks for the corresponding session in (first)
the internal session cache (unless SSL_SESS_CACHE_NO_INTERNAL_LOOKUP is set),
then (second) in the external cache if available. If the session is found, the
server will try to reuse the session. This is the default.
=item SSL_SESS_CACHE_BOTH
@ -77,12 +80,31 @@ explicitly by the application.
=item SSL_SESS_CACHE_NO_INTERNAL_LOOKUP
By setting this flag sessions are cached in the internal storage but
they are not looked up automatically. If an external session cache
is enabled, sessions are looked up in the external cache. As automatic
lookup only applies for SSL/TLS servers, the flag has no effect on
By setting this flag, session-resume operations in an SSL/TLS server will not
automatically look up sessions in the internal cache, even if sessions are
automatically stored there. If external session caching callbacks are in use,
this flag guarantees that all lookups are directed to the external cache.
As automatic lookup only applies for SSL/TLS servers, the flag has no effect on
clients.
=item SSL_SESS_CACHE_NO_INTERNAL_STORE
Depending on the presence of SSL_SESS_CACHE_CLIENT and/or SSL_SESS_CACHE_SERVER,
sessions negotiated in an SSL/TLS handshake may be cached for possible reuse.
Normally a new session is added to the internal cache as well as any external
session caching (callback) that is configured for the SSL_CTX. This flag will
prevent sessions being stored in the internal cache (though the application can
add them manually using L<SSL_CTX_add_session(3)|SSL_CTX_add_session(3)>). Note:
in any SSL/TLS servers where external caching is configured, any successful
session lookups in the external cache (ie. for session-resume requests) would
normally be copied into the local cache before processing continues - this flag
prevents these additions to the internal cache as well.
=item SSL_SESS_CACHE_NO_INTERNAL
Enable both SSL_SESS_CACHE_NO_INTERNAL_LOOKUP and
SSL_SESS_CACHE_NO_INTERNAL_STORE at the same time.
=back
The default mode is SSL_SESS_CACHE_SERVER.
@ -98,6 +120,7 @@ SSL_CTX_get_session_cache_mode() returns the currently set cache mode.
L<ssl(3)|ssl(3)>, L<SSL_set_session(3)|SSL_set_session(3)>,
L<SSL_session_reused(3)|SSL_session_reused(3)>,
L<SSL_CTX_add_session(3)|SSL_CTX_add_session(3)>,
L<SSL_CTX_sess_number(3)|SSL_CTX_sess_number(3)>,
L<SSL_CTX_sess_set_cache_size(3)|SSL_CTX_sess_set_cache_size(3)>,
L<SSL_CTX_sess_set_get_cb(3)|SSL_CTX_sess_set_get_cb(3)>,

7
ssl/ssl.h
View File

@ -726,10 +726,11 @@ struct ssl_ctx_st
#define SSL_SESS_CACHE_SERVER 0x0002
#define SSL_SESS_CACHE_BOTH (SSL_SESS_CACHE_CLIENT|SSL_SESS_CACHE_SERVER)
#define SSL_SESS_CACHE_NO_AUTO_CLEAR 0x0080
/* This one, when set, makes the server session-id lookup not look
* in the cache. If there is an application get_session callback
* defined, this will still get called. */
/* enough comments already ... see SSL_CTX_set_session_cache_mode(3) */
#define SSL_SESS_CACHE_NO_INTERNAL_LOOKUP 0x0100
#define SSL_SESS_CACHE_NO_INTERNAL_STORE 0x0200
#define SSL_SESS_CACHE_NO_INTERNAL \
(SSL_SESS_CACHE_NO_INTERNAL_LOOKUP|SSL_SESS_CACHE_NO_INTERNAL_STORE)
struct lhash_st *SSL_CTX_sessions(SSL_CTX *ctx);
#define SSL_CTX_sess_number(ctx) \

2
ssl/ssl_lib.c
View File

@ -1803,7 +1803,7 @@ void ssl_update_cache(SSL *s,int mode)
i=s->ctx->session_cache_mode;
if ((i & mode) && (!s->hit)
&& ((i & SSL_SESS_CACHE_NO_INTERNAL_LOOKUP)
&& ((i & SSL_SESS_CACHE_NO_INTERNAL_STORE)
|| SSL_CTX_add_session(s->ctx,s->session))
&& (s->ctx->new_session_cb != NULL))
{

9
ssl/ssl_sess.c
View File

@ -309,9 +309,12 @@ int ssl_get_prev_session(SSL *s, unsigned char *session_id, int len)
if (copy)
CRYPTO_add(&ret->references,1,CRYPTO_LOCK_SSL_SESSION);
/* The following should not return 1, otherwise,
* things are very strange */
SSL_CTX_add_session(s->ctx,ret);
/* Add the externally cached session to the internal
* cache as well if and only if we are supposed to. */
if(!(s->ctx->session_cache_mode & SSL_SESS_CACHE_NO_INTERNAL_STORE))
/* The following should not return 1, otherwise,
* things are very strange */
SSL_CTX_add_session(s->ctx,ret);
}
if (ret == NULL)
goto err;