bug#54624: 29.0.50; textsec and ipv6 addresses

[Robert Pluim]

>>>>> On Mon, 4 Apr 2022 14:48:37 +0200, Mattias Engdegård <mattiase@acm.org> 
>>>>> said:

    Mattias> 4 apr. 2022 kl. 12.42 skrev Lars Ingebrigtsen <larsi@gnus.org>:
    >> Fine by me, but addresses that are too long should be suspicious (to
    >> catch people obfuscating by doing things like 000000000000000127.0.0.1
    >> and similar).  That's what I was intending to catch with the {} things
    >> without having to actually do the hard maths myself.  :-)

    Mattias> I agree that is desirable. If a strict parse is impractical (not 
sure if it is), what about something slightly stricter than what we current 
have? Here is a straw-man proposal:

    Mattias>     (rx-let ((octet (or "0" (: (in "1-9") (? (in "0-9") (? (in 
"0-9"))))))
    Mattias>              (ipv4 (: octet (= 3 "."  octet)))
    Mattias>              (hextet (** 1 4 (in "0-9a-f")))
    Mattias>              (ipv6 (: (? "::") hextet (* ":" (? ":") hextet)
    Mattias>                       (? (or "::" (: ":" ipv4) )))))
    Mattias>       (rx bos (or ipv4 ipv6 (: "[" ipv6 "]")) eos))

    Mattias> and don't forget to bind case-fold-search to nil while calling 
string-match-p since IPv6 specifies lower-case hex digits.

    Mattias> And thanks to Andreas for reminding me about IPv6 allowing dotted 
quads as well.

Or we just arrange it so that thereʼs a primitive that maps to calling
getaddrinfo(3) with AI_NUMERICHOST in the hints.ai_flags (but Lars'
motivation here is 'not suspicious', not 'looks like a numeric IP
address', so maybe not).

Robert
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