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fix(mapper): prevent index out of bounds in ToEndpointName with multi-dot suffix #6433

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fix(mapper): prevent index out of bounds in ToEndpointName with multi-dot suffix #6433

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30 changes: 17 additions & 13 deletions registry/mapper/mapper.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,8 @@ package mapper
import (
"strings"

log "github.com/sirupsen/logrus"

"sigs.k8s.io/external-dns/endpoint"
)

Expand Down Expand Up @@ -73,40 +75,42 @@ func (a AffixNameMapper) ToEndpointName(dns string) (string, string) {
// drop suffix
if a.isSuffix() {
dc := strings.Count(a.suffix, ".")
DNSName := strings.SplitN(lowerDNSName, ".", 2+dc)
domainWithSuffix := strings.Join(DNSName[:1+dc], ".")

r, rType := a.dropAffixExtractType(domainWithSuffix)
if !strings.Contains(lowerDNSName, ".") {
parts := strings.SplitN(lowerDNSName, ".", 2+dc)
if len(parts) <= dc {
log.Debugf("skipping TXT record %q: too few labels for suffix %q", dns, a.suffix)
return "", ""
}
r, rType := a.dropAffixExtractType(strings.Join(parts[:1+dc], "."))
if len(parts) <= 1+dc {
return r, rType
}
Comment on lines 76 to 86
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@ivankatliarchuk ivankatliarchuk May 19, 2026

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I could be wrong here. The early-exit guard calling dropAffixExtractType(lowerDNSName) when there are too few labels is fine, but it's misleading - the name can't possibly match the suffix at that point, so it always returns ("", ""). Being explicit is cleaner. Also, domainWithSuffix can be inlined:

if a.isSuffix() {
      dc := strings.Count(a.suffix, ".")
      parts := strings.SplitN(lowerDNSName, ".", 2+dc)
      if len(parts) <= dc {
          log.Debugf("skipping TXT record %q: too few labels for suffix %q", dns, a.suffix)
          return "", ""
      }
      r, rType := a.dropAffixExtractType(strings.Join(parts[:1+dc], "."))
      if len(parts) <= 1+dc {
          return r, rType
      }
      return r + "." + parts[1+dc], rType
  }

^ Same algorithm, no slightly misleading fallthrough call, no intermediate variable. The parts name is also more conventional than DNSName in Go.

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@carterpewpew carterpewpew May 19, 2026

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I have addressed this as well in the latest commit

return r + "." + DNSName[1+dc], rType
return r + "." + parts[1+dc], rType
}
return "", ""
}

func (a AffixNameMapper) ToTXTName(dns, recordType string) string {
DNSName := strings.SplitN(dns, ".", 2)
parts := strings.SplitN(dns, ".", 2)
recordType = strings.ToLower(recordType)
recordT := recordType + "-"

prefix := a.normalizeAffixTemplate(a.prefix, recordType)
suffix := a.normalizeAffixTemplate(a.suffix, recordType)

// If specified, replace a leading asterisk in the generated txt record name with some other string
if a.wildcardReplacement != "" && DNSName[0] == "*" {
DNSName[0] = a.wildcardReplacement
if a.wildcardReplacement != "" && parts[0] == "*" {
parts[0] = a.wildcardReplacement
}

if !a.recordTypeInAffix() {
DNSName[0] = recordT + DNSName[0]
parts[0] = recordT + parts[0]
}

if len(DNSName) < 2 {
return prefix + DNSName[0] + suffix
if len(parts) < 2 {
return prefix + parts[0] + suffix
}

return prefix + DNSName[0] + suffix + "." + DNSName[1]
return prefix + parts[0] + suffix + "." + parts[1]
}

func (a AffixNameMapper) recordTypeInAffix() bool {
Expand Down
21 changes: 21 additions & 0 deletions registry/mapper/mapper_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,27 @@ func TestAffixNameMapper_ToEndpointName(t *testing.T) {
wantEndpointName: "foo.example.com",
wantRecordType: endpoint.RecordTypeCNAME,
},
{
name: "suffix with multiple dots and trailing labels",
mapper: NewAffixNameMapper("", ".foo.bar", ""),
input: "a-example.foo.bar.com",
wantEndpointName: "example.com",
wantRecordType: endpoint.RecordTypeA,
},
{
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@ivankatliarchuk ivankatliarchuk May 19, 2026

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There is no direct test case for the full path with trailing labels - e.g., a-example.foo.bar.com with suffix .foo.bar should return ("example.com", "A"). The TestToEndpointNameNewTXT round-trip test for "suffix with multiple dots" covers a 3-dot suffix case indirectly, but adding an explicit assertion for trailing labels with a 2-dot suffix would close the gap and document the expected behavior.

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@carterpewpew carterpewpew May 19, 2026

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You're right, that was an oversight on my part. Added an explicit test for a-example.foo.bar.com with suffix .foo.bar expecting ("example.com", "A").

name: "suffix with multiple dots and no trailing labels",
mapper: NewAffixNameMapper("", ".foo.bar", ""),
input: "a-example.foo.bar",
wantEndpointName: "example",
wantRecordType: endpoint.RecordTypeA,
},
{
name: "suffix with multiple dots and too few labels does not panic",
mapper: NewAffixNameMapper("", ".foo.bar", ""),
input: "a-example.foo",
wantEndpointName: "",
wantRecordType: "",
},
{
name: "no affix with A record",
mapper: NewAffixNameMapper("", "", ""),
Expand Down