From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Jonathan S. Katz" <jkatz@postgresql.org>
cc: Michael Paquier <michael@paquier.xyz>, pgsql-bugs@lists.postgresql.org,
        Stephen Frost <sfrost@snowman.net>
Subject: Re: Possible to store invalid SCRAM-SHA-256 Passwords
In-reply-to: <5a93333c-dde6-ee52-f870-4dccfc50eb6f@postgresql.org>
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 <5a93333c-dde6-ee52-f870-4dccfc50eb6f@postgresql.org>
Comments: In-reply-to "Jonathan S. Katz" <jkatz@postgresql.org>
	message dated "Mon, 22 Apr 2019 18:32:45 -0400"
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Date: Mon, 22 Apr 2019 18:42:01 -0400
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"Jonathan S. Katz" <jkatz@postgresql.org> writes:
> OK, so I have something that sort of works, i.e:

> if (strncmp(shadow_pass, "md5", 3) == 0 &&
>     strlen(shadow_pass) == MD5_PASSWD_LEN &&
>     strspn(shadow_pass, MD5_PASSWD_CHARSET) == MD5_PASSWD_LEN
> )

> where MD5_PASSWD_CHARSET = "mabcdef0123456789"

> ...but you may notice something: the CHARSET contains an "m" as we store
> that "md5" prefix on the md5 hashed passwords.

Yeah, that's silly; why not

     strspn(shadow_pass + 3, MD5_PASSWD_CHARSET) == MD5_PASSWD_LEN - 3

It's not like this code isn't very well aware of the first 3 characters
being not like the others.

			regards, tom lane