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in dkim-signature header, allow FWS anywhere in "z=" (copied headers), and prevent panic in cli command "mox dkim verify" when a dkim-signature cannot be parsed

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the BNF for "z=" does not show FWS is allowed (while it does in other places,
eg base64), but the text above the BNF explains it in words.
This commit is contained in:
Mechiel Lukkien 2023-02-03 13:29:47 +01:00
parent 2239f38232
commit ba077dadd0
No known key found for this signature in database
3 changed files with 67 additions and 40 deletions
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81
dkim/parser.go
View file

@ -51,13 +51,21 @@ func (p *parser) xtaken(n int) string {
return r
}
func (p *parser) xtakefn(fn func(c rune, i int) bool) string {
func (p *parser) xtakefn(ignoreFWS bool, fn func(c rune, i int) bool) string {
var r string
for i, c := range p.s[p.o:] {
if !fn(c, i) {
return p.xtaken(i)
switch c {
case ' ', '\t', '\r', '\n':
continue
}
p.xtaken(i)
return r
}
r += string(c)
}
return p.xtaken(len(p.s) - p.o)
p.xtaken(len(p.s) - p.o)
return r
}
func (p *parser) empty() bool {
@ -70,21 +78,28 @@ func (p *parser) xnonempty() {
}
}
func (p *parser) xtakefn1(fn func(c rune, i int) bool) string {
func (p *parser) xtakefn1(ignoreFWS bool, fn func(c rune, i int) bool) string {
var r string
p.xnonempty()
for i, c := range p.s[p.o:] {
if !fn(c, i) {
switch c {
case ' ', '\t', '\r', '\n':
continue
}
if i == 0 {
p.xerrorf("expected at least 1 char")
}
return p.xtaken(i)
p.xtaken(i)
return r
}
r += string(c)
}
return p.xtaken(len(p.s) - p.o)
}
func (p *parser) wsp() {
p.xtakefn(func(c rune, i int) bool {
p.xtakefn(false, func(c rune, i int) bool {
return c == ' ' || c == '\t'
})
}
@ -124,7 +139,7 @@ func (p *parser) take(s string) bool {
// ../rfc/6376:657
func (p *parser) xtagName() string {
return p.xtakefn1(func(c rune, i int) bool {
return p.xtakefn1(false, func(c rune, i int) bool {
return isalpha(c) || i > 0 && (isdigit(c) || c == '_')
})
}
@ -134,9 +149,9 @@ func (p *parser) xalgorithm() (string, string) {
xtagx := func(c rune, i int) bool {
return isalpha(c) || i > 0 && isdigit(c)
}
algk := p.xtakefn1(xtagx)
algk := p.xtakefn1(false, xtagx)
p.xtake("-")
algv := p.xtakefn1(xtagx)
algv := p.xtakefn1(false, xtagx)
return algk, algv
}
@ -145,7 +160,7 @@ func (p *parser) xalgorithm() (string, string) {
// ../rfc/6376:1076
func (p *parser) xbase64() []byte {
s := ""
p.xtakefn(func(c rune, i int) bool {
p.xtakefn(false, func(c rune, i int) bool {
if isalphadigit(c) || c == '+' || c == '/' || c == '=' {
s += string(c)
return true
@ -185,9 +200,9 @@ func (p *parser) xdomain() dns.Domain {
// todo: add a "lax" mode where underscore is allowed if this is a selector? seen in the wild, but invalid: ../rfc/6376:581 ../rfc/5321:2303
return isalphadigit(c) || (i > 0 && c == '-' && p.o+1 < len(p.s))
}
s := p.xtakefn1(subdomain)
s := p.xtakefn1(false, subdomain)
for p.hasPrefix(".") {
s += p.xtake(".") + p.xtakefn1(subdomain)
s += p.xtake(".") + p.xtakefn1(false, subdomain)
}
d, err := dns.ParseDomain(s)
if err != nil {
@ -196,23 +211,24 @@ func (p *parser) xdomain() dns.Domain {
return d
}
func (p *parser) xhdrName() string {
func (p *parser) xhdrName(ignoreFWS bool) string {
// ../rfc/6376:473
// ../rfc/5322:1689
// BNF for hdr-name (field-name) allows ";", but DKIM disallows unencoded semicolons. ../rfc/6376:643
return p.xtakefn1(func(c rune, i int) bool {
// ignoreFWS is needed for "z=", which can have FWS anywhere. ../rfc/6376:1372
return p.xtakefn1(ignoreFWS, func(c rune, i int) bool {
return c > ' ' && c < 0x7f && c != ':' && c != ';'
})
}
func (p *parser) xsignedHeaderFields() []string {
// ../rfc/6376:1157
l := []string{p.xhdrName()}
l := []string{p.xhdrName(false)}
for p.peekfws(":") {
p.fws()
p.xtake(":")
p.fws()
l = append(l, p.xhdrName())
l = append(l, p.xhdrName(false))
}
return l
}
@ -304,7 +320,7 @@ func (p *parser) xchar() rune {
}
func (p *parser) xatom() string {
return p.xtakefn1(func(c rune, i int) bool {
return p.xtakefn1(false, func(c rune, i int) bool {
switch c {
case '!', '#', '$', '%', '&', '\'', '*', '+', '-', '/', '=', '?', '^', '_', '`', '{', '|', '}', '~':
return true
@ -362,7 +378,7 @@ func (p *parser) xqtagmethod() string {
if strings.EqualFold(s, "dns") && len(rem) >= len("/txt") && strings.EqualFold(rem[:len("/txt")], "/txt") {
s += p.xtaken(4)
} else if p.take("/") {
s += "/" + p.xqp(true, true)
s += "/" + p.xqp(true, true, false)
}
return s
}
@ -381,25 +397,27 @@ func isalphadigit(c rune) bool {
// ../rfc/6376:469
func (p *parser) xhyphenatedWord() string {
return p.xtakefn1(func(c rune, i int) bool {
return p.xtakefn1(false, func(c rune, i int) bool {
return isalpha(c) || i > 0 && isdigit(c) || i > 0 && c == '-' && p.o+i+1 < len(p.s) && isalphadigit(rune(p.s[p.o+i+1]))
})
}
// ../rfc/6376:474
func (p *parser) xqphdrvalue() string {
return p.xqp(true, false)
func (p *parser) xqphdrvalue(ignoreFWS bool) string {
return p.xqp(true, false, ignoreFWS)
}
func (p *parser) xqpSection() string {
return p.xqp(false, false)
return p.xqp(false, false, false)
}
// dkim-quoted-printable (pipeEncoded true) or qp-section.
//
// It is described in terms of (lots of) modifications to MIME quoted-printable,
// but it may be simpler to just ignore that reference.
func (p *parser) xqp(pipeEncoded, colonEncoded bool) string {
//
// ignoreFWS is required for "z=", which can have FWS anywhere.
func (p *parser) xqp(pipeEncoded, colonEncoded, ignoreFWS bool) string {
// ../rfc/6376:494 ../rfc/2045:1260
hex := func(c byte) rune {
@ -418,12 +436,8 @@ func (p *parser) xqp(pipeEncoded, colonEncoded bool) string {
if colonEncoded && p.hasPrefix(":") {
break
}
if p.hasPrefix("=") {
p.xtake("=")
// note: \r\n before the full hex-octet has been encountered in the wild. Could be
// a sender just wrapping their headers after escaping, or not escaping an "=". We
// currently don't compensate for it.
h := p.xtakefn(func(c rune, i int) bool {
if p.take("=") {
h := p.xtakefn(ignoreFWS, func(c rune, i int) bool {
return i < 2 && (c >= '0' && c <= '9' || c >= 'A' && c <= 'Z')
})
if len(h) != 2 {
@ -433,7 +447,7 @@ func (p *parser) xqp(pipeEncoded, colonEncoded bool) string {
s += string(c)
continue
}
x := p.xtakefn(func(c rune, i int) bool {
x := p.xtakefn(ignoreFWS, func(c rune, i int) bool {
return c > ' ' && c < 0x7f && c != ';' && c != '=' && !(pipeEncoded && c == '|')
})
if x == "" {
@ -465,10 +479,11 @@ func (p *parser) xcopiedHeaderFields() []string {
}
func (p *parser) xztagcopy() string {
// ../rfc/6376:1386
f := p.xhdrName()
// ABNF does not mention FWS (unlike for other fields), but FWS is allowed everywhere in the value...
// ../rfc/6376:1386 ../rfc/6376:1372
f := p.xhdrName(true)
p.fws()
p.xtake(":")
v := p.xqphdrvalue()
v := p.xqphdrvalue(true)
return f + ":" + v
}

2
dkim/sig.go
View file

@ -213,7 +213,7 @@ func parseSignature(buf []byte, smtputf8 bool) (sig *Sig, verifySig []byte, err
ds := newSigWithDefaults()
seen := map[string]struct{}{}
p := parser{s: string(buf), smtputf8: smtputf8}
name := p.xhdrName()
name := p.xhdrName(false)
if !strings.EqualFold(name, "DKIM-Signature") {
xerrorf("%w", errSigHeader)
}

24
main.go
View file

@ -1123,13 +1123,25 @@ that was passed.
xcheckf(err, "dkim verify")
for _, result := range results {
record, err := result.Record.Record()
if err != nil {
log.Printf("warning: record: %s", err)
var sigh string
if result.Sig == nil {
log.Printf("warning: could not parse signature")
} else {
sigh, err = result.Sig.Header()
if err != nil {
log.Printf("warning: packing signature: %s", err)
}
}
sigh, err := result.Sig.Header()
xcheckf(err, "packing dkim-signature header")
fmt.Printf("status %q, err %v\nrecord %s\nheader %s\n", result.Status, result.Err, record, sigh)
var txt string
if result.Record == nil {
log.Printf("warning: missing DNS record")
} else {
txt, err = result.Record.Record()
if err != nil {
log.Printf("warning: packing record: %s", err)
}
}
fmt.Printf("status %q, err %v\nrecord %q\nheader %s\n", result.Status, result.Err, txt, sigh)
}
}