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| author | Benjamin Kaduk <bkaduk@akamai.com> | 2017-02-07 23:23:16 +0100 |
|---|---|---|
| committer | Rich Salz <rsalz@openssl.org> | 2017-04-10 17:57:37 +0200 |
| commit | 8313a787d770ac1d7ddafcbc41b13e7fb5841eae (patch) | |
| tree | b035e51f740d0abee2d5242eebd97f844f94fd3e | |
| parent | Fix util/mkdef.pl (diff) | |
| download | openssl-8313a787d770ac1d7ddafcbc41b13e7fb5841eae.tar.xz openssl-8313a787d770ac1d7ddafcbc41b13e7fb5841eae.zip | |
Allow an ALPN callback to pretend to not exist
RFC 7301 mandates that the server SHALL respond with a fatal
"no_application_protocol" alert when there is no overlap between
the client's supplied list and the server's list of supported protocols.
In commit 062178678f5374b09f00d70796f6e692e8775aca we changed from
ignoring non-success returns from the supplied alpn_select_cb() to
treating such non-success returns as indicative of non-overlap and
sending the fatal alert.
In effect, this is using the presence of an alpn_select_cb() as a proxy
to attempt to determine whether the application has configured a list
of supported protocols. However, there may be cases in which an
application's architecture leads it to supply an alpn_select_cb() but
have that callback be configured to take no action on connections that
do not have ALPN configured; returning SSL_TLSEXT_ERR_NOACK from
the callback would be the natural way to do so. Unfortunately, the
aforementioned behavior change also treated SSL_TLSEXT_ERR_NOACK as
indicative of no overlap and terminated the connection; this change
supplies special handling for SSL_TLSEXT_ERR_NOACK returns from the
callback. In effect, it provides a way for a callback to obtain the
behavior that would have occurred if no callback was registered at
all, which was not possible prior to this change.
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2570)
| -rw-r--r-- | doc/man3/SSL_CTX_set_alpn_select_cb.pod | 8 | ||||
| -rw-r--r-- | ssl/statem/extensions.c | 3 | ||||
| -rw-r--r-- | test/handshake_helper.c | 2 |
3 files changed, 11 insertions, 2 deletions
diff --git a/doc/man3/SSL_CTX_set_alpn_select_cb.pod b/doc/man3/SSL_CTX_set_alpn_select_cb.pod index 5ff5a93b52..5ad063eb7f 100644 --- a/doc/man3/SSL_CTX_set_alpn_select_cb.pod +++ b/doc/man3/SSL_CTX_set_alpn_select_cb.pod @@ -113,9 +113,15 @@ The ALPN select callback B<cb>, must return one of the following: ALPN protocol selected. +=item SSL_TLSEXT_ERR_ALERT_FATAL + +There was no overlap between the client's supplied list and the server +configuration. + =item SSL_TLSEXT_ERR_NOACK -ALPN protocol not selected. +ALPN protocol not selected, e.g., because no ALPN protocols are configured for +this connection. =back diff --git a/ssl/statem/extensions.c b/ssl/statem/extensions.c index cd1d0bd3ec..7ec7128172 100644 --- a/ssl/statem/extensions.c +++ b/ssl/statem/extensions.c @@ -919,6 +919,9 @@ static int final_alpn(SSL *s, unsigned int context, int sent, int *al) /* ALPN takes precedence over NPN. */ s->s3->npn_seen = 0; #endif + } else if (r == SSL_TLSEXT_ERR_NOACK) { + /* Behave as if no callback was present. */ + return 1; } else { *al = SSL_AD_NO_APPLICATION_PROTOCOL; return 0; diff --git a/test/handshake_helper.c b/test/handshake_helper.c index 47af3fe396..94fa5c578f 100644 --- a/test/handshake_helper.c +++ b/test/handshake_helper.c @@ -413,7 +413,7 @@ static int server_alpn_cb(SSL *s, const unsigned char **out, *out = tmp_out; /* Unlike NPN, we don't tolerate a mismatch. */ return ret == OPENSSL_NPN_NEGOTIATED ? SSL_TLSEXT_ERR_OK - : SSL_TLSEXT_ERR_NOACK; + : SSL_TLSEXT_ERR_ALERT_FATAL; } #ifndef OPENSSL_NO_SRP |