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core: Allow loopback hosts for admin endpoint (fix #5650) (#5664)

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Matt Holt 2023-08-02 11:13:52 -06:00 committed by GitHub
parent 5c51c1db2c
commit f66493efef
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2 changed files with 43 additions and 14 deletions
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25
admin.go
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@ -318,7 +318,32 @@ func (admin AdminConfig) allowedOrigins(addr NetworkAddress) []*url.URL {
// messages. If the requested URI does not include an Internet host
// name for the service being requested, then the Host header field MUST
// be given with an empty value."
//
// UPDATE July 2023: Go broke this by patching a minor security bug in 1.20.6.
// Understandable, but frustrating. See:
// https://github.com/golang/go/issues/60374
// See also the discussion here:
// https://github.com/golang/go/issues/61431
//
// We can no longer conform to RFC 2616 Section 14.26 from either Go or curl
// in purity. (Curl allowed no host between 7.40 and 7.50, but now requires a
// bogus host; see https://superuser.com/a/925610.) If we disable Host/Origin
// security checks, the infosec community assures me that it is secure to do
// so, because:
// 1) Browsers do not allow access to unix sockets
// 2) DNS is irrelevant to unix sockets
//
// I am not quite ready to trust either of those external factors, so instead
// of disabling Host/Origin checks, we now allow specific Host values when
// accessing the admin endpoint over unix sockets. I definitely don't trust
// DNS (e.g. I don't trust 'localhost' to always resolve to the local host),
// and IP shouldn't even be used, but if it is for some reason, I think we can
// at least be reasonably assured that 127.0.0.1 and ::1 route to the local
// machine, meaning that a hypothetical browser origin would have to be on the
// local machine as well.
uniqueOrigins[""] = struct{}{}
uniqueOrigins["127.0.0.1"] = struct{}{}
uniqueOrigins["::1"] = struct{}{}
} else {
uniqueOrigins[net.JoinHostPort("localhost", addr.port())] = struct{}{}
uniqueOrigins[net.JoinHostPort("::1", addr.port())] = struct{}{}

32
cmd/commandfuncs.go
View file

@ -610,7 +610,7 @@ func AdminAPIRequest(adminAddr, method, uri string, headers http.Header, body io
}
origin := "http://" + parsedAddr.JoinHostPort(0)
if parsedAddr.IsUnixNetwork() {
origin = "http://unixsocket" // hack so that http.NewRequest() is happy
origin = "http://127.0.0.1" // bogus host is a hack so that http.NewRequest() is happy
}
// form the request
@ -619,20 +619,24 @@ func AdminAPIRequest(adminAddr, method, uri string, headers http.Header, body io
return nil, fmt.Errorf("making request: %v", err)
}
if parsedAddr.IsUnixNetwork() {
// When listening on a unix socket, the admin endpoint doesn't
// accept any Host header because there is no host:port for
// a unix socket's address. The server's host check is fairly
// strict for security reasons, so we don't allow just any
// Host header. For unix sockets, the Host header must be
// empty. Unfortunately, Go makes it impossible to make HTTP
// requests with an empty Host header... except with this one
// weird trick. (Hopefully they don't fix it. It's already
// hard enough to use HTTP over unix sockets.)
// We used to conform to RFC 2616 Section 14.26 which requires
// an empty host header when there is no host, as is the case
// with unix sockets. However, Go required a Host value so we
// used a hack of a space character as the host (it would see
// the Host was non-empty, then trim the space later). As of
// Go 1.20.6 (July 2023), this hack no longer works. See:
// https://github.com/golang/go/issues/60374
// See also the discussion here:
// https://github.com/golang/go/issues/61431
//
// An equivalent curl command would be something like:
// $ curl --unix-socket caddy.sock http:/:$REQUEST_URI
req.URL.Host = " "
req.Host = ""
// After that, we now require a Host value of either 127.0.0.1
// or ::1 if one is set. Above I choose to use 127.0.0.1. Even
// though the value should be completely irrelevant (it could be
// "srldkjfsd"), if for some reason the Host *is* used, at least
// we can have some reasonable assurance it will stay on the local
// machine and that browsers, if they ever allow access to unix
// sockets, can still enforce CORS, ensuring it is still coming
// from the local machine.
} else {
req.Header.Set("Origin", origin)
}