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crypto/tls: ensure the server picked an advertised ALPN protocol

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This is a SHALL in RFC 7301, Section 3.2.

Also some more cleanup after NPN, which worked the other way around
(with the possibility that the client could pick a protocol the server
did not suggest).

Change-Id: I83cc43ca1b3c686dfece8315436441c077065d82
Reviewed-on: https://go-review.googlesource.com/c/go/+/239748
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Filippo Valsorda <filippo@golang.org>
Trust: Roland Shoemaker <roland@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
This commit is contained in:
Filippo Valsorda 2020-06-24 17:01:00 -04:00
parent 74ff83e750
commit 3e0f07eb2d
6 changed files with 30 additions and 30 deletions
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33
handshake_client.go
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@ -705,18 +705,18 @@ func (hs *clientHandshakeState) processServerHello() (bool, error) {
}
}
clientDidALPN := len(hs.hello.alpnProtocols) > 0
serverHasALPN := len(hs.serverHello.alpnProtocol) > 0
if !clientDidALPN && serverHasALPN {
c.sendAlert(alertHandshakeFailure)
return false, errors.New("tls: server advertised unrequested ALPN extension")
}
if serverHasALPN {
if hs.serverHello.alpnProtocol != "" {
if len(hs.hello.alpnProtocols) == 0 {
c.sendAlert(alertUnsupportedExtension)
return false, errors.New("tls: server advertised unrequested ALPN extension")
}
if mutualProtocol([]string{hs.serverHello.alpnProtocol}, hs.hello.alpnProtocols) == "" {
c.sendAlert(alertUnsupportedExtension)
return false, errors.New("tls: server selected unadvertised ALPN protocol")
}
c.clientProtocol = hs.serverHello.alpnProtocol
c.clientProtocolFallback = false
}
c.scts = hs.serverHello.scts
if !hs.serverResumedSession() {
@ -973,20 +973,17 @@ func clientSessionCacheKey(serverAddr net.Addr, config *Config) string {
return serverAddr.String()
}
// mutualProtocol finds the mutual Next Protocol Negotiation or ALPN protocol
// given list of possible protocols and a list of the preference order. The
// first list must not be empty. It returns the resulting protocol and flag
// indicating if the fallback case was reached.
func mutualProtocol(protos, preferenceProtos []string) (string, bool) {
// mutualProtocol finds the mutual ALPN protocol given list of possible
// protocols and a list of the preference order.
func mutualProtocol(protos, preferenceProtos []string) string {
for _, s := range preferenceProtos {
for _, c := range protos {
if s == c {
return s, false
return s
}
}
}
return protos[0], true
return ""
}
// hostnameInSNI converts name into an appropriate hostname for SNI.