From 3760e016850398b85094c4c99e955b8c3dea5711 Mon Sep 17 00:00:00 2001 From: Peter Moody Date: Wed, 23 Dec 2015 13:51:54 -0800 Subject: [PATCH] x/crypto/ssh: add function to parse known_hosts files. Change-Id: I9258ecf2b38258e31bcb6e73ac042ad8125fd2d1 Reviewed-on: https://go-review.googlesource.com/18106 Reviewed-by: Peter Moody Reviewed-by: Adam Langley --- ssh/keys.go | 74 ++++++++++++++++++++++++++ ssh/keys_test.go | 131 +++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 205 insertions(+) diff --git a/ssh/keys.go b/ssh/keys.go index 8ce4185..cfc970b 100644 --- a/ssh/keys.go +++ b/ssh/keys.go @@ -19,6 +19,7 @@ import ( "fmt" "io" "math/big" + "strings" ) // These constants represent the algorithm names for key types supported by this @@ -77,6 +78,79 @@ func parseAuthorizedKey(in []byte) (out PublicKey, comment string, err error) { return out, comment, nil } +// ParseKnownHosts parses an entry in the format of the known_hosts file. +// +// The known_hosts format is documented in the sshd(8) manual page. This +// function will parse a single entry from in. On successful return, marker +// will contain the optional marker value (i.e. "cert-authority" or "revoked") +// or else be empty, hosts will contain the hosts that this entry matches, +// pubKey will contain the public key and comment will contain any trailing +// comment at the end of the line. See the sshd(8) manual page for the various +// forms that a host string can take. +// +// The unparsed remainder of the input will be returned in rest. This function +// can be called repeatedly to parse multiple entries. +// +// If no entries were found in the input then err will be io.EOF. Otherwise a +// non-nil err value indicates a parse error. +func ParseKnownHosts(in []byte) (marker string, hosts []string, pubKey PublicKey, comment string, rest []byte, err error) { + for len(in) > 0 { + end := bytes.IndexByte(in, '\n') + if end != -1 { + rest = in[end+1:] + in = in[:end] + } else { + rest = nil + } + + end = bytes.IndexByte(in, '\r') + if end != -1 { + in = in[:end] + } + + in = bytes.TrimSpace(in) + if len(in) == 0 || in[0] == '#' { + in = rest + continue + } + + i := bytes.IndexAny(in, " \t") + if i == -1 { + in = rest + continue + } + + // Strip out the begining of the known_host key. + // This is either an optional marker or a (set of) hostname(s). + keyFields := bytes.Fields(in) + if len(keyFields) < 3 || len(keyFields) > 5 { + return "", nil, nil, "", nil, errors.New("ssh: invalid entry in known_hosts data") + } + + // keyFields[0] is either "@cert-authority", "@revoked" or a comma separated + // list of hosts + marker := "" + if keyFields[0][0] == '@' { + marker = string(keyFields[0][1:]) + keyFields = keyFields[1:] + } + + hosts := string(keyFields[0]) + // keyFields[1] contains the key type (e.g. “ssh-rsa”). + // However, that information is duplicated inside the + // base64-encoded key and so is ignored here. + + key := bytes.Join(keyFields[2:], []byte(" ")) + if pubKey, comment, err = parseAuthorizedKey(key); err != nil { + return "", nil, nil, "", nil, err + } + + return marker, strings.Split(hosts, ","), pubKey, comment, rest, nil + } + + return "", nil, nil, "", nil, io.EOF +} + // ParseAuthorizedKeys parses a public key from an authorized_keys // file used in OpenSSH according to the sshd(8) manual page. func ParseAuthorizedKey(in []byte) (out PublicKey, comment string, options []string, rest []byte, err error) { diff --git a/ssh/keys_test.go b/ssh/keys_test.go index b4cceaf..2756947 100644 --- a/ssh/keys_test.go +++ b/ssh/keys_test.go @@ -304,3 +304,134 @@ func TestInvalidEntry(t *testing.T) { t.Errorf("got valid entry for %q", authInvalid) } } + +var knownHostsParseTests = []struct { + input string + err string + + marker string + comment string + hosts []string + rest string +} { + { + "", + "EOF", + + "", "", nil, "", + }, + { + "# Just a comment", + "EOF", + + "", "", nil, "", + }, + { + " \t ", + "EOF", + + "", "", nil, "", + }, + { + "localhost ssh-rsa {RSAPUB}", + "", + + "", "", []string{"localhost"}, "", + }, + { + "localhost\tssh-rsa {RSAPUB}", + "", + + "", "", []string{"localhost"}, "", + }, + { + "localhost\tssh-rsa {RSAPUB}\tcomment comment", + "", + + "", "comment comment", []string{"localhost"}, "", + }, + { + "localhost\tssh-rsa {RSAPUB}\tcomment comment\n", + "", + + "", "comment comment", []string{"localhost"}, "", + }, + { + "localhost\tssh-rsa {RSAPUB}\tcomment comment\r\n", + "", + + "", "comment comment", []string{"localhost"}, "", + }, + { + "localhost\tssh-rsa {RSAPUB}\tcomment comment\r\nnext line", + "", + + "", "comment comment", []string{"localhost"}, "next line", + }, + { + "localhost,[host2:123]\tssh-rsa {RSAPUB}\tcomment comment", + "", + + "", "comment comment", []string{"localhost","[host2:123]"}, "", + }, + { + "@marker \tlocalhost,[host2:123]\tssh-rsa {RSAPUB}", + "", + + "marker", "", []string{"localhost","[host2:123]"}, "", + }, + { + "@marker \tlocalhost,[host2:123]\tssh-rsa aabbccdd", + "short read", + + "", "", nil, "", + }, +} + +func TestKnownHostsParsing(t *testing.T) { + rsaPub, rsaPubSerialized := getTestKey() + + for i, test := range knownHostsParseTests { + var expectedKey PublicKey + const rsaKeyToken = "{RSAPUB}" + + input := test.input + if strings.Contains(input, rsaKeyToken) { + expectedKey = rsaPub + input = strings.Replace(test.input, rsaKeyToken, rsaPubSerialized, -1) + } + + marker, hosts, pubKey, comment, rest, err := ParseKnownHosts([]byte(input)) + if err != nil { + if len(test.err) == 0 { + t.Errorf("#%d: unexpectedly failed with %q", i, err) + } else if !strings.Contains(err.Error(), test.err) { + t.Errorf("#%d: expected error containing %q, but got %q", i, test.err, err) + } + continue + } else if len(test.err) != 0 { + t.Errorf("#%d: succeeded but expected error including %q", i, test.err) + continue + } + + if !reflect.DeepEqual(expectedKey, pubKey) { + t.Errorf("#%d: expected key %#v, but got %#v", i, expectedKey, pubKey) + } + + if marker != test.marker { + t.Errorf("#%d: expected marker %q, but got %q", i, test.marker, marker) + } + + if comment != test.comment { + t.Errorf("#%d: expected comment %q, but got %q", i, test.comment, comment) + } + + if !reflect.DeepEqual(test.hosts, hosts) { + t.Errorf("#%d: expected hosts %#v, but got %#v", i, test.hosts, hosts) + } + + if rest := string(rest); rest != test.rest { + t.Errorf("#%d: expected remaining input to be %q, but got %q", i, test.rest, rest) + } + } +}