117 lines
4.2 KiB
Diff
117 lines
4.2 KiB
Diff
From 7e4d731b1c07201ad9374c1cd9ac5263bdf35bce Mon Sep 17 00:00:00 2001
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From: Matt Caswell <matt@openssl.org>
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Date: Tue, 5 Mar 2024 15:43:53 +0000
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Subject: [PATCH] Fix unconstrained session cache growth in TLSv1.3
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In TLSv1.3 we create a new session object for each ticket that we send.
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We do this by duplicating the original session. If SSL_OP_NO_TICKET is in
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use then the new session will be added to the session cache. However, if
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early data is not in use (and therefore anti-replay protection is being
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used), then multiple threads could be resuming from the same session
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simultaneously. If this happens and a problem occurs on one of the threads,
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then the original session object could be marked as not_resumable. When we
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duplicate the session object this not_resumable status gets copied into the
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new session object. The new session object is then added to the session
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cache even though it is not_resumable.
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Subsequently, another bug means that the session_id_length is set to 0 for
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sessions that are marked as not_resumable - even though that session is
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still in the cache. Once this happens the session can never be removed from
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the cache. When that object gets to be the session cache tail object the
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cache never shrinks again and grows indefinitely.
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CVE-2024-2511
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Reviewed-by: Neil Horman <nhorman@openssl.org>
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Reviewed-by: Tomas Mraz <tomas@openssl.org>
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(Merged from https://github.com/openssl/openssl/pull/24044)
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---
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ssl/ssl_lib.c | 5 +++--
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ssl/ssl_sess.c | 28 ++++++++++++++++++++++------
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ssl/statem/statem_srvr.c | 5 ++---
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3 files changed, 27 insertions(+), 11 deletions(-)
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diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
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index b5cc4af2f0302..e747b7f90aa71 100644
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--- a/ssl/ssl_lib.c
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+++ b/ssl/ssl_lib.c
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@@ -3737,9 +3737,10 @@ void ssl_update_cache(SSL *s, int mode)
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/*
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* If the session_id_length is 0, we are not supposed to cache it, and it
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- * would be rather hard to do anyway :-)
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+ * would be rather hard to do anyway :-). Also if the session has already
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+ * been marked as not_resumable we should not cache it for later reuse.
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*/
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- if (s->session->session_id_length == 0)
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+ if (s->session->session_id_length == 0 || s->session->not_resumable)
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return;
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/*
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diff --git a/ssl/ssl_sess.c b/ssl/ssl_sess.c
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index bf84e792251b8..241cf43c46296 100644
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--- a/ssl/ssl_sess.c
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+++ b/ssl/ssl_sess.c
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@@ -154,16 +154,11 @@ SSL_SESSION *SSL_SESSION_new(void)
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return ss;
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}
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-SSL_SESSION *SSL_SESSION_dup(const SSL_SESSION *src)
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-{
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- return ssl_session_dup(src, 1);
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-}
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-
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/*
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* Create a new SSL_SESSION and duplicate the contents of |src| into it. If
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* ticket == 0 then no ticket information is duplicated, otherwise it is.
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*/
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-SSL_SESSION *ssl_session_dup(const SSL_SESSION *src, int ticket)
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+static SSL_SESSION *ssl_session_dup_intern(const SSL_SESSION *src, int ticket)
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{
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SSL_SESSION *dest;
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@@ -287,6 +282,27 @@ SSL_SESSION *ssl_session_dup(const SSL_SESSION *src, int ticket)
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return NULL;
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}
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+SSL_SESSION *SSL_SESSION_dup(const SSL_SESSION *src)
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+{
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+ return ssl_session_dup_intern(src, 1);
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+}
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+
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+/*
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+ * Used internally when duplicating a session which might be already shared.
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+ * We will have resumed the original session. Subsequently we might have marked
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+ * it as non-resumable (e.g. in another thread) - but this copy should be ok to
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+ * resume from.
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+ */
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+SSL_SESSION *ssl_session_dup(const SSL_SESSION *src, int ticket)
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+{
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+ SSL_SESSION *sess = ssl_session_dup_intern(src, ticket);
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+
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+ if (sess != NULL)
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+ sess->not_resumable = 0;
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+
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+ return sess;
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+}
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+
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const unsigned char *SSL_SESSION_get_id(const SSL_SESSION *s, unsigned int *len)
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{
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if (len)
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diff --git a/ssl/statem/statem_srvr.c b/ssl/statem/statem_srvr.c
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index 5d59d53563ed8..8e493176f658e 100644
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--- a/ssl/statem/statem_srvr.c
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+++ b/ssl/statem/statem_srvr.c
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@@ -2338,9 +2338,8 @@ int tls_construct_server_hello(SSL *s, WPACKET *pkt)
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* so the following won't overwrite an ID that we're supposed
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* to send back.
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*/
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- if (s->session->not_resumable ||
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- (!(s->ctx->session_cache_mode & SSL_SESS_CACHE_SERVER)
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- && !s->hit))
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+ if (!(s->ctx->session_cache_mode & SSL_SESS_CACHE_SERVER)
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+ && !s->hit)
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s->session->session_id_length = 0;
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if (usetls13) {
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