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Code to thread-safety in ChangeCipherState

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The server-side ChangeCipherState processing stores the new cipher
in the SSL_SESSION object, so that the new state can be used if
this session gets resumed.  However, writing to the session is only
thread-safe for initial handshakes, as at other times the session
object may be in a shared cache and in use by another thread at the
same time.  Reflect this invariant in the code by only writing to
s->session->cipher when it is currently NULL (we do not cache sessions
with no cipher).  The code prior to this change would never actually
change the (non-NULL) cipher value in a session object, since our
server enforces that (pre-TLS-1.3) resumptions use the exact same
cipher as the initial connection, and non-abbreviated renegotiations
have produced a new session object before we get to this point.
Regardless, include logic to detect such a condition and abort the
handshake if it occurs, to avoid any risk of inadvertently using
the wrong cipher on a connection.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/10943)
This commit is contained in:
Benjamin Kaduk 2020-01-24 13:44:27 -08:00 committed by Benjamin Kaduk
parent d74014c4b8
commit 2e3ec2e157
3 changed files with 11 additions and 1 deletions
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1
crypto/err/openssl.txt
View File

@ -1310,6 +1310,7 @@ SSL_F_OSSL_STATEM_SERVER_CONSTRUCT_MESSAGE:431:*
SSL_F_OSSL_STATEM_SERVER_POST_PROCESS_MESSAGE:601:\
ossl_statem_server_post_process_message
SSL_F_OSSL_STATEM_SERVER_POST_WORK:602:ossl_statem_server_post_work
SSL_F_OSSL_STATEM_SERVER_PRE_WORK:640:
SSL_F_OSSL_STATEM_SERVER_PROCESS_MESSAGE:603:ossl_statem_server_process_message
SSL_F_OSSL_STATEM_SERVER_READ_TRANSITION:418:ossl_statem_server_read_transition
SSL_F_OSSL_STATEM_SERVER_WRITE_TRANSITION:604:\

1
include/openssl/sslerr.h
View File

@ -94,6 +94,7 @@ int ERR_load_SSL_strings(void);
# define SSL_F_OSSL_STATEM_SERVER_CONSTRUCT_MESSAGE 0
# define SSL_F_OSSL_STATEM_SERVER_POST_PROCESS_MESSAGE 0
# define SSL_F_OSSL_STATEM_SERVER_POST_WORK 0
# define SSL_F_OSSL_STATEM_SERVER_PRE_WORK 0
# define SSL_F_OSSL_STATEM_SERVER_PROCESS_MESSAGE 0
# define SSL_F_OSSL_STATEM_SERVER_READ_TRANSITION 0
# define SSL_F_OSSL_STATEM_SERVER_WRITE_TRANSITION 0

10
ssl/statem/statem_srvr.c
View File

@ -744,7 +744,15 @@ WORK_STATE ossl_statem_server_pre_work(SSL *s, WORK_STATE wst)
case TLS_ST_SW_CHANGE:
if (SSL_IS_TLS13(s))
break;
s->session->cipher = s->s3.tmp.new_cipher;
/* Writes to s->session are only safe for initial handshakes */
if (s->session->cipher == NULL) {
s->session->cipher = s->s3.tmp.new_cipher;
} else if (s->session->cipher != s->s3.tmp.new_cipher) {
SSLfatal(s, SSL_AD_INTERNAL_ERROR,
SSL_F_OSSL_STATEM_SERVER_PRE_WORK,
ERR_R_INTERNAL_ERROR);
return WORK_ERROR;
}
if (!s->method->ssl3_enc->setup_key_block(s)) {
/* SSLfatal() already called */
return WORK_ERROR;