| 1 | package aviso |
| 2 | |
| 3 | import ( |
| 4 | "errors" |
| 5 | "fmt" |
| 6 | "net" |
| 7 | "net/http" |
| 8 | "net/url" |
| 9 | "syscall" |
| 10 | "time" |
| 11 | ) |
| 12 | |
| 13 | // ErrBadEndpoint means a subscription endpoint was refused before any |
| 14 | // request: wrong scheme, credentials, fragment, too long, or an |
| 15 | // address no push service lives at. |
| 16 | var ErrBadEndpoint = errors.New("aviso: endpoint refused") |
| 17 | |
| 18 | const maxEndpointLen = 2048 |
| 19 | |
| 20 | // validateEndpoint is the request-time half of the SSRF guard: shape |
| 21 | // and literal-IP checks. The dial-time half (guardedIP in the dialer's |
| 22 | // Control) catches what a hostname resolves to, which this cannot. |
| 23 | func validateEndpoint(raw string) error { |
| 24 | if raw == "" || len(raw) > maxEndpointLen { |
| 25 | return fmt.Errorf("%w: empty or over %d bytes", ErrBadEndpoint, maxEndpointLen) |
| 26 | } |
| 27 | u, err := url.Parse(raw) |
| 28 | if err != nil || u.Scheme != "https" || u.Host == "" || u.Hostname() == "" || |
| 29 | u.User != nil || u.Fragment != "" || u.RawFragment != "" { |
| 30 | return fmt.Errorf("%w: must be https, no credentials, no fragment", ErrBadEndpoint) |
| 31 | } |
| 32 | if ip := net.ParseIP(u.Hostname()); ip != nil { |
| 33 | if err := guardedIP(ip); err != nil { |
| 34 | return fmt.Errorf("%w: %v", ErrBadEndpoint, err) |
| 35 | } |
| 36 | } |
| 37 | return nil |
| 38 | } |
| 39 | |
| 40 | // reservedNets are the ranges net.IP's own predicates do not cover, |
| 41 | // from IANA's special-purpose registries: "this network", IETF |
| 42 | // protocol assignments, the documentation and benchmarking nets, |
| 43 | // class E; and for IPv6 the discard prefix, benchmarking, both |
| 44 | // documentation prefixes, and the NAT64 prefixes — the well-known one |
| 45 | // and RFC 8215's local-use one, whose low 32 bits are an IPv4 address |
| 46 | // the IPv4 rules would otherwise never see, and which a local |
| 47 | // translator may point at private space. |
| 48 | var reservedNets = func() []*net.IPNet { |
| 49 | var out []*net.IPNet |
| 50 | for _, c := range []string{ |
| 51 | "0.0.0.0/8", "192.0.0.0/24", "192.0.2.0/24", "198.18.0.0/15", |
| 52 | "198.51.100.0/24", "203.0.113.0/24", "240.0.0.0/4", |
| 53 | "64:ff9b::/96", "64:ff9b:1::/48", "100::/64", "2001:2::/48", |
| 54 | "2001:db8::/32", "3fff::/20", |
| 55 | } { |
| 56 | _, n, err := net.ParseCIDR(c) |
| 57 | if err != nil { |
| 58 | panic(err) |
| 59 | } |
| 60 | out = append(out, n) |
| 61 | } |
| 62 | return out |
| 63 | }() |
| 64 | |
| 65 | // guardedIP refuses every address a push service cannot legitimately |
| 66 | // have: loopback, private, link-local, unspecified, multicast, CGNAT, |
| 67 | // the reserved ranges above, and their IPv4-mapped forms. Applied at |
| 68 | // connect time so DNS rebinding after validation still fails. |
| 69 | func guardedIP(ip net.IP) error { |
| 70 | if ip == nil { |
| 71 | return errors.New("address is not an IP") |
| 72 | } |
| 73 | if ip4 := ip.To4(); ip4 != nil { |
| 74 | ip = ip4 |
| 75 | } |
| 76 | refuse := func() error { return fmt.Errorf("address %s is not routable to a push service", ip) } |
| 77 | switch { |
| 78 | case ip.IsLoopback(), ip.IsPrivate(), ip.IsLinkLocalUnicast(), ip.IsLinkLocalMulticast(), |
| 79 | ip.IsUnspecified(), ip.IsMulticast(), ip.IsInterfaceLocalMulticast(): |
| 80 | return refuse() |
| 81 | } |
| 82 | if len(ip) == net.IPv4len && ip[0] == 100 && ip[1]&0xc0 == 64 { // 100.64.0.0/10, CGNAT |
| 83 | return refuse() |
| 84 | } |
| 85 | for _, n := range reservedNets { |
| 86 | if n.Contains(ip) { |
| 87 | return refuse() |
| 88 | } |
| 89 | } |
| 90 | return nil |
| 91 | } |
| 92 | |
| 93 | // newClient is the only HTTP client that ever talks to a push |
| 94 | // service: no redirects (a push service never redirects, and following |
| 95 | // one is how a validated URL turns into an internal one), no proxy |
| 96 | // from the environment (same reason), and the IP guard inside the |
| 97 | // dialer's Control so it runs on the address actually connected to. |
| 98 | func newClient() *http.Client { |
| 99 | dialer := &net.Dialer{ |
| 100 | Timeout: 10 * time.Second, |
| 101 | Control: func(network, address string, _ syscall.RawConn) error { |
| 102 | host, _, err := net.SplitHostPort(address) |
| 103 | if err != nil { |
| 104 | return fmt.Errorf("aviso: dial: %w", err) |
| 105 | } |
| 106 | ip := net.ParseIP(host) |
| 107 | if ip == nil { |
| 108 | return fmt.Errorf("aviso: dial: %q is not an IP", host) |
| 109 | } |
| 110 | if err := guardedIP(ip); err != nil { |
| 111 | return fmt.Errorf("aviso: dial refused: %w", err) |
| 112 | } |
| 113 | return nil |
| 114 | }, |
| 115 | } |
| 116 | return &http.Client{ |
| 117 | Timeout: 30 * time.Second, |
| 118 | Transport: &http.Transport{ |
| 119 | Proxy: nil, |
| 120 | DialContext: dialer.DialContext, |
| 121 | TLSHandshakeTimeout: 10 * time.Second, |
| 122 | MaxIdleConns: 64, |
| 123 | IdleConnTimeout: 90 * time.Second, |
| 124 | }, |
| 125 | CheckRedirect: func(*http.Request, []*http.Request) error { |
| 126 | return errors.New("aviso: push service redirected; refused") |
| 127 | }, |
| 128 | } |
| 129 | } |
| 130 | |
amadan