lib-ssl-iostream: Process ServerName in ssl_clienthello_callback() when possible

diff --git a/src/lib-ssl-iostream/iostream-openssl-context.c b/src/lib-ssl-iostream/iostream-openssl-context.c
index b9066421245a27c162d5766851e887f150cd7971..e53ea17c1c517399563e6d6a0b30292eecc20854 100644 (file)
--- a/src/lib-ssl-iostream/iostream-openssl-context.c
+++ b/src/lib-ssl-iostream/iostream-openssl-context.c
@@ -321,6 +321,8 @@ static int ssl_servername_process(struct ssl_iostream *ssl_io, const char *host,
        return 0;
 }
 
+#ifndef HAVE_SSL_client_hello_get0_ciphers
+
 static int ssl_servername_callback(SSL *ssl, int *al,
                                   void *context ATTR_UNUSED)
 {
@@ -340,7 +342,7 @@ static int ssl_servername_callback(SSL *ssl, int *al,
        return SSL_TLSEXT_ERR_OK;
 }
 
-#ifdef HAVE_SSL_client_hello_get0_ciphers
+#else
 
 static const int ssl_ja3_grease[] = {
        0x0a0a,
@@ -422,7 +424,34 @@ static int ssl_ja3_nid_to_cid(int nid)
        return nid;
 }
 
-static int ssl_clienthello_callback(SSL *ssl, int *al ATTR_UNUSED,
+static const char *extract_server_name(const unsigned char *ext, size_t extlen)
+{
+       /* must have two byte veclen, two bytes for
+          index and type, and two bytes for length
+          and actual name. */
+       if (extlen < 2 + 2 + 2)
+               return NULL;
+       /* Vector length first */
+       unsigned short veclen = be16_to_cpu_unaligned(ext);
+       if (veclen + 2U != extlen)
+               return NULL;
+       ext += 2;
+       extlen -= 2;
+       /* Expecting only host_name as first ServerName,
+          we also only support max 255 character host names,
+          so if the first byte of the length is non-zero,
+          reject as well. */
+       if (ext[0] != TLSEXT_NAMETYPE_host_name || ext[1] != 0)
+               return NULL;
+       ext += 2;
+       extlen -= 2;
+       unsigned char namelen = ext[0];
+       if (namelen > extlen - 1)
+               return NULL;
+       return t_strdup_until(ext + 1, ext + 1 + namelen);
+}
+
+static int ssl_clienthello_callback(SSL *ssl, int *al,
                                    void *context ATTR_UNUSED)
 {
        struct ssl_iostream *ssl_io =
@@ -499,6 +528,17 @@ static int ssl_clienthello_callback(SSL *ssl, int *al ATTR_UNUSED,
        i_free(ssl_io->ja3_str);
        ssl_io->ja3_str = i_strdup(str_c(ja3));
 
+       /* Process extension 0 - server_name */
+       const char *host = NULL;
+       if (SSL_client_hello_get0_ext(ssl, TLSEXT_TYPE_server_name,
+                                     &ext, &extlen) == 1 &&
+           extlen > 0)
+               host = extract_server_name(ext, extlen);
+
+       /* host can be NULL, but that's ok. */
+       if (ssl_servername_process(ssl_io, host, al) < 0)
+               return SSL_CLIENT_HELLO_ERROR;
+
        return SSL_CLIENT_HELLO_SUCCESS;
 }
 
@@ -639,11 +679,12 @@ ssl_iostream_context_set(struct ssl_iostream_context *ctx,
                }
        }
        if (!ctx->client_ctx) {
+#ifdef HAVE_SSL_client_hello_get0_ciphers
+               SSL_CTX_set_client_hello_cb(ctx->ssl_ctx, ssl_clienthello_callback, ctx);
+#else
                if (SSL_CTX_set_tlsext_servername_callback(ctx->ssl_ctx,
                                        ssl_servername_callback) != 1)
                        i_unreached();
-#ifdef HAVE_SSL_client_hello_get0_ciphers
-               SSL_CTX_set_client_hello_cb(ctx->ssl_ctx, ssl_clienthello_callback, ctx);
 #endif
        }
        return 0;