From cadbbd51c8b4e66515cd3e97754cfeda606c7b15 Mon Sep 17 00:00:00 2001
From: Rob Stradling <rob@comodo.com>
Date: Tue, 10 Sep 2013 12:41:37 +0100
Subject: Don't prefer ECDHE-ECDSA ciphers when the client appears to be Safari
 on OS X. OS X 10.8..10.8.3 has broken support for ECDHE-ECDSA ciphers.

---
 ssl/t1_lib.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)

(limited to 'ssl/t1_lib.c')

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index d56456e14d..621b214b7b 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -344,6 +344,89 @@ unsigned char *ssl_add_serverhello_tlsext(SSL *s, unsigned char *p, unsigned cha
 	return ret;
 	}
 
+#ifndef OPENSSL_NO_EC
+/* ssl_check_for_safari attempts to fingerprint Safari using OS X
+ * SecureTransport using the TLS extension block in |d|, of length |n|.
+ * Safari, since 10.6, sends exactly these extensions, in this order:
+ *   SNI,
+ *   elliptic_curves
+ *   ec_point_formats
+ *
+ * We wish to fingerprint Safari because they broke ECDHE-ECDSA support in 10.8,
+ * but they advertise support. So enabling ECDHE-ECDSA ciphers breaks them.
+ * Sadly we cannot differentiate 10.6, 10.7 and 10.8.4 (which work), from
+ * 10.8..10.8.3 (which don't work).
+ */
+static void ssl_check_for_safari(SSL *s, const unsigned char *data, const unsigned char *d, int n) {
+	unsigned short type, size;
+	static const unsigned char kSafariExtensionsBlock[] = {
+		0x00, 0x0a,  /* elliptic_curves extension */
+		0x00, 0x08,  /* 8 bytes */
+		0x00, 0x06,  /* 6 bytes of curve ids */
+		0x00, 0x17,  /* P-256 */
+		0x00, 0x18,  /* P-384 */
+		0x00, 0x19,  /* P-521 */
+
+		0x00, 0x0b,  /* ec_point_formats */
+		0x00, 0x02,  /* 2 bytes */
+		0x01,        /* 1 point format */
+		0x00,        /* uncompressed */
+	};
+
+	/* The following is only present in TLS 1.2 */
+	static const unsigned char kSafariTLS12ExtensionsBlock[] = {
+		0x00, 0x0d,  /* signature_algorithms */
+		0x00, 0x0c,  /* 12 bytes */
+		0x00, 0x0a,  /* 10 bytes */
+		0x05, 0x01,  /* SHA-384/RSA */
+		0x04, 0x01,  /* SHA-256/RSA */
+		0x02, 0x01,  /* SHA-1/RSA */
+		0x04, 0x03,  /* SHA-256/ECDSA */
+		0x02, 0x03,  /* SHA-1/ECDSA */
+	};
+
+	if (data >= (d+n-2))
+		return;
+	data += 2;
+
+	if (data > (d+n-4))
+		return;
+	n2s(data,type);
+	n2s(data,size);
+
+	if (type != TLSEXT_TYPE_server_name)
+		return;
+
+	if (data+size > d+n)
+		return;
+	data += size;
+
+	if (TLS1_get_version(s) >= TLS1_2_VERSION)
+		{
+		const size_t len1 = sizeof(kSafariExtensionsBlock);
+		const size_t len2 = sizeof(kSafariTLS12ExtensionsBlock);
+
+		if (data + len1 + len2 != d+n)
+			return;
+		if (memcmp(data, kSafariExtensionsBlock, len1) != 0)
+			return;
+		if (memcmp(data + len1, kSafariTLS12ExtensionsBlock, len2) != 0)
+			return;
+		}
+	else
+		{
+		const size_t len = sizeof(kSafariExtensionsBlock);
+
+		if (data + len != d+n)
+			return;
+		if (memcmp(data, kSafariExtensionsBlock, len) != 0)
+			return;
+		}
+
+	s->s3->is_probably_safari = 1;
+}
+#endif	/* OPENSSL_NO_EC */
+
 int ssl_parse_clienthello_tlsext(SSL *s, unsigned char **p, unsigned char *d, int n, int *al)
 	{
 	unsigned short type;
@@ -355,6 +438,11 @@ int ssl_parse_clienthello_tlsext(SSL *s, unsigned char **p, unsigned char *d, in
 	s->servername_done = 0;
 	s->tlsext_status_type = -1;
 
+#ifndef OPENSSL_NO_EC
+	if (s->options & SSL_OP_SAFARI_ECDHE_ECDSA_BUG)
+		ssl_check_for_safari(s, data, d, n);
+#endif	/* OPENSSL_NO_EC */
+
 	if (data >= (d+n-2))
 		goto ri_check;
 
-- 
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