Don't leave stale sequence numbers behind in ssl3_clear()libressl-v3.2.5

A TLS client doing session reuse in a certain way could run into
a use-after-free. Set the sequence numbers inside ssl3_clear() to
make sure this points at valid memory and do the initialization of
the record layer a bit earlier so that this works as desired.
Additionally, explicitly clear the sequence numbers in ssl3_free()
which would have turned the use-after-free into a NULL dereference.

Issue reported by Ilya Chipitsine.

Fix from jsing

This is errata/6.8/017_libssl.patch.sig

1 files changed, 10 insertions, 1 deletions

diff --git a/src/lib/libssl/s3_lib.c b/src/lib/libssl/s3_lib.c
index 91bfb5f3b6..97dd2005c2 100644
--- a/src/lib/libssl/s3_lib.c
+++ b/src/lib/libssl/s3_lib.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: s3_lib.c,v 1.198 2020/09/17 15:42:14 jsing Exp $ */
+/* $OpenBSD: s3_lib.c,v 1.198.4.1 2021/03/15 15:59:04 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -1577,6 +1577,10 @@ ssl3_free(SSL *s)
 
         free(S3I(s)->alpn_selected);
 
+        /* Clear reference to sequence numbers. */
+        tls12_record_layer_clear_read_state(s->internal->rl);
+        tls12_record_layer_clear_write_state(s->internal->rl);
+
         freezero(S3I(s), sizeof(*S3I(s)));
         freezero(s->s3, sizeof(*s->s3));
 
@@ -1649,6 +1653,11 @@ ssl3_clear(SSL *s)
         s->internal->packet_length = 0;
         s->version = TLS1_VERSION;
 
+        tls12_record_layer_set_read_seq_num(s->internal->rl,
+            S3I(s)->read_sequence);
+        tls12_record_layer_set_write_seq_num(s->internal->rl,
+            S3I(s)->write_sequence);
+
         S3I(s)->hs.state = SSL_ST_BEFORE|((s->server) ? SSL_ST_ACCEPT : SSL_ST_CONNECT);
 }