From a21b71daf57a54a12c2aedff0fba0860fa977590 Mon Sep 17 00:00:00 2001 From: Daniel McCarney Date: Thu, 15 May 2025 13:41:14 -0400 Subject: [PATCH] crypto/tls: have servers prefer TLS 1.3 when supported Previously the common Config.mutualVersion() code prioritized the selected version based on the provided peerVersions being sent in peer preference order. Instead we would prefer to see TLS 1.3 used whenever it is supported, even if the peer would prefer an older protocol version. This commit updates mutualVersions() to implement this policy change. Our new behaviour matches the behaviour of other TLS stacks, notably BoringSSL, and so also allows enabling the IgnoreClientVersionOrder BoGo test that we otherwise must skip. Updates #72006 Change-Id: I27a2cd231e4b8762b0d9e2dbd3d8ddd5b87fd5cb Reviewed-on: https://go-review.googlesource.com/c/go/+/673236 Auto-Submit: Daniel McCarney TryBot-Bypass: Daniel McCarney Reviewed-by: David Chase Reviewed-by: Roland Shoemaker --- doc/next/6-stdlib/99-minor/crypto/tls/version_pref.md | 1 + src/crypto/tls/bogo_config.json | 1 - src/crypto/tls/common.go | 6 +++--- 3 files changed, 4 insertions(+), 4 deletions(-) create mode 100644 doc/next/6-stdlib/99-minor/crypto/tls/version_pref.md diff --git a/doc/next/6-stdlib/99-minor/crypto/tls/version_pref.md b/doc/next/6-stdlib/99-minor/crypto/tls/version_pref.md new file mode 100644 index 0000000000..5686f3ca0a --- /dev/null +++ b/doc/next/6-stdlib/99-minor/crypto/tls/version_pref.md @@ -0,0 +1 @@ +TLS servers now prefer the highest supported protocol version, even if it isn't the client's most preferred protocol version. diff --git a/src/crypto/tls/bogo_config.json b/src/crypto/tls/bogo_config.json index 61585938d7..191f48fc02 100644 --- a/src/crypto/tls/bogo_config.json +++ b/src/crypto/tls/bogo_config.json @@ -66,7 +66,6 @@ "SupportTicketsWithSessionID": "TODO: first pass, this should be fixed", "NoNullCompression-TLS12": "TODO: first pass, this should be fixed", "KeyUpdate-RequestACK": "TODO: first pass, this should be fixed", - "IgnoreClientVersionOrder": "RFC 8446 4.2.1 says supported_versions is in client pref order", "SupportedVersionSelection-TLS12": "TODO: first pass, this should be fixed", "DuplicateExtensionServer-TLS-TLS1": "TODO: first pass, this should be fixed", "DuplicateExtensionClient-TLS-TLS1": "TODO: first pass, this should be fixed", diff --git a/src/crypto/tls/common.go b/src/crypto/tls/common.go index 71b9ddb02c..1aaad7aba1 100644 --- a/src/crypto/tls/common.go +++ b/src/crypto/tls/common.go @@ -1233,11 +1233,11 @@ func (c *Config) supportsCurve(version uint16, curve CurveID) bool { } // mutualVersion returns the protocol version to use given the advertised -// versions of the peer. Priority is given to the peer preference order. +// versions of the peer. The highest supported version is preferred. func (c *Config) mutualVersion(isClient bool, peerVersions []uint16) (uint16, bool) { supportedVersions := c.supportedVersions(isClient) - for _, v := range peerVersions { - if slices.Contains(supportedVersions, v) { + for _, v := range supportedVersions { + if slices.Contains(peerVersions, v) { return v, true } } -- 2.50.0