While doing some work on bug 37060, the refactoring of StrToHostAddr and StrToHostAddr6 in the sockets
unit,(https://bugs.freepascal.org/view.php?id=37060), I found that StrToHostAddr is doing no validation at all on input address characters before calling the function Val, so any Pascal notation that Val accepts, such as 0x and $ for hexadecimal, % for binary, & for octal, and mathematical signs are all accepted in ipv4 octets.

https://bugs.freepascal.org/view.php?id=37080

As a consequence, StrToHostAddr will happily parse addresses like these:

0xa.3.4.5
9.$c.4.5
%1111.%11001110.30.4
&7.&5.30.4
12.+4.1.1

Any number in any notation will be accepted as long as byte overflow isn't triggered. Thus, + in octets is accepted, but - is not, because the function detects that the octet is negative which then triggers overflow.

Fixing this is outside the scope of the patch I'm preparing for 37060, but if no-one else feels inclined to look into this by the time I'm finished with that patch then I'll submit a new patch for it.

Fixed.

Michael.

That must be a new record in bug fix speed. You fixed that within ten minutes of my message to the list!

I forgot to mention in my message, but did mention in the bug report, that leading zeroes are also allowed, so you can parse:

0000000001.1.1.1

Personally I don't think this is a problem (mathematically, you can add as many zeroes as you like), but I can imagine some do, so I fixed it.

Rev. 45368.

Michael.

Well, the same argument could be made for allowing hexadecimal or other notations. But ip address representation formats aren't just numbers, they're textual representations meant for easy transmission between programs and across networks, and the standards documents are quite clear about what's allowed in them and what's not. If StrToHostAddr breaks with those standards and accepts addresses that other implementations won't, or rejects addresses others accept, that makes it unusable for programs that must operate in mixed language environments.

In my own case, I'm writing a program to parse and validate SPF records, as defined in RFC7208. SPF records are read and processed by SMTP servers as they receive mail, so any tools that attempt to validate SPF records must not accept as valid any ipv4 or ipv6 address that the SMTP server won't also accept.

I added a note to https://bugs.freepascal.org/view.php?id=37013 about the fact that this test program fails if range checking is enabled (I don't know if the range error is in StrToHostAddr6 or in the test program itself).

Jonas

I will check.
I never use range checking, so that could have easily escaped me.

Michael.

Fixed 2 occurrences of a range check.

Michael.

D'oh! Normally I'm scrupulous about turning on range checks in my own programs, but I completely forgot to do that here. But I see Michael has already fixed it.

Looking at the code in SVN, I spotted a couple of still extant references to s6_addr16 instead of u6_addr16 in StrToHostAddr6. It's possible to trigger range check errors for them. All s6_addr16s should be u6_addr16s.

If you try parsing an address like '::ffff' it will hit this part of the code.

Sorry for the screw-up. Normally I religiously use range checks in my own code, but it completely went out of my head when working on this.

That's what you get when communication with someone who doesn't use them: It's contagious ;-)

I'll have a look.

Michael.

Op 15-05-2020 om 12:48 schreef Michael Van Canneyt:

Ahh.. why.. 😢

An ip-address of 0xa.&5.%11001110.3 is just funny. 😀

Regards,

Joost.