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util/dnsname: do not allow labels starting with a digit

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This disallows labels that start with digits (as per RFC 1035 section
2.3.1). The invalid character error text is also improved so that UTF-8
sequences are properly copied to the error rather than an encoding of
the first byte.

Updates #13858

Change-Id: Ib3fea46559918e7bba6b11c1ca33ede61755bd52
Signed-off-by: Adrian Dewhurst <adrian@tailscale.com>
This commit is contained in:
Adrian Dewhurst 2024-10-18 11:48:43 -04:00
parent c0a9895748
commit 9c04e30735
2 changed files with 57 additions and 5 deletions
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8
util/dnsname/dnsname.go
View File

@ -102,8 +102,8 @@ func ValidLabel(label string) error {
if len(label) > maxLabelLength {
return fmt.Errorf("%q is too long, max length is %d bytes", label, maxLabelLength)
}
if !isalphanum(label[0]) {
return fmt.Errorf("%q is not a valid DNS label: must start with a letter or number", label)
if !isalpha(label[0]) {
return fmt.Errorf("%q is not a valid DNS label: must start with a letter", label)
}
if !isalphanum(label[len(label)-1]) {
return fmt.Errorf("%q is not a valid DNS label: must end with a letter or number", label)
@ -111,9 +111,9 @@ func ValidLabel(label string) error {
if len(label) < 2 {
return nil
}
for i := 1; i < len(label)-1; i++ {
for i, c := range label {
if !isdnschar(label[i]) {
return fmt.Errorf("%q is not a valid DNS label: contains invalid character %q", label, label[i])
return fmt.Errorf("%q is not a valid DNS label: contains invalid character %q", label, c)
}
}
return nil

54
util/dnsname/dnsname_test.go
View File

@ -192,8 +192,9 @@ func TestValidHostname(t *testing.T) {
}{
{"example", ""},
{"example.com", ""},
{" example", `must start with a letter or number`},
{" example", `must start with a letter`},
{"example-.com", `must end with a letter or number`},
{"www.2example.com", `must start with a letter`},
{strings.Repeat("a", 63), ""},
{strings.Repeat("a", 64), `is too long, max length is 63 bytes`},
{strings.Repeat(strings.Repeat("a", 63)+".", 4), "is too long to be a DNS name"},
@ -230,3 +231,54 @@ func BenchmarkToFQDN(b *testing.B) {
})
}
}
func TestValidLabel(t *testing.T) {
tests := []struct {
label string
wantErr string
}{
{"", "empty DNS label"},
{strings.Repeat("a", 63), ""},
{strings.Repeat("a", 64), "is too long, max length is 63 bytes"},
{"a", ""},
{"A", ""},
{"1", "must start with a letter"},
{"-", "must start with a letter"},
{"$", "must start with a letter"},
{"$abc", "must start with a letter"},
{"1abc", "must start with a letter"},
{"-abc", "must start with a letter"},
{"az", ""},
{"aZ", ""},
{"Az", ""},
{"A5", ""},
{"A-", "must end with a letter or number"},
{"A$", "must end with a letter or number"},
{"abcd", ""},
{"aBcD", ""},
{"aBc9", ""},
{"aBc$", "must end with a letter or number"},
{"aBc-", "must end with a letter or number"},
{"1Bcd", "must start with a letter"},
{"-Bcd", "must start with a letter"},
{"%Bcd", "must start with a letter"},
{"A--d", ""},
{"A---", "must end with a letter or number"},
{"A234", ""},
{"A^34", "contains invalid character '^'"},
{"a.b", "contains invalid character '.'"},
{"what🤦lol", "contains invalid character '🤦'"},
{"truncated\xf0\x90\x8dz", "contains invalid character '\ufffd'"},
{"invalid\xe2\x28\xa1z", "contains invalid character '\ufffd'"},
{"overlong\xc1\x81z", "contains invalid character '\ufffd'"},
}
for _, tt := range tests {
t.Run(tt.label, func(t *testing.T) {
err := ValidLabel(tt.label)
if (err == nil) != (tt.wantErr == "") || (err != nil && !strings.HasSuffix(err.Error(), tt.wantErr)) {
t.Fatalf("ValidLabel(%s)=%v; expected %v", tt.label, err, tt.wantErr)
}
})
}
}