Date: Sun, 15 Feb 2015 00:17:13 +0100 From: Jilles Tjoelker <jilles@stack.nl> To: "Derek (freebsd lists)" <482254ac@razorfever.net> Cc: freebsd-security@FreeBSD.org, John-Mark Gurney <jmg@funkthat.com>, "A.J. Kehoe IV \(Nanoman\)" <nanoman@nanoman.ca>, delphij@FreeBSD.org Subject: Re: [patch] libcrypt & friends - modular crypt format support in /etc/login.conf Message-ID: <20150214231712.GA1360@stack.nl> In-Reply-To: <54D9F8DF.7070904@razorfever.net> References: <54D9F8DF.7070904@razorfever.net>
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On Tue, Feb 10, 2015 at 07:26:07AM -0500, Derek (freebsd lists) wrote:
> I've been working on this for a while, and I've produced a patch
> that does a few things with the base system:
> 1. allows modular crypt to be specified as passwd_format in
> /etc/login.conf
> - this allows setting the algorithm *and rounds*, i.e. $2b$10$
> for users of varying classes.
> - this will allow any future algorithms and parameters
> supported by crypt(3) to be supported by the tools around login.conf
OK.
> 2. introduces a new api, crypt_makesalt which will generate an
> appropriate salt for any algorithm selected
I like the idea.
> 3. updates userland to use this API, and removes totally the
> {crypt_set_format, login_setcryptfmt, login_getcryptfmt} APIs
Removing API functions completely requires a SHLIB_MAJOR bump. I think
this can be avoided by replacing the functions with a stub instead, so
they would behave as if the default always applied and not allow changes
to it.
> 4. switches crypt algorithms to use thread-local storage, so the
> good old global crypt buffer is thread-local
This uses quite a bit of memory for each thread created, even if it does
not call crypt() at all. Fortunately, libcrypt is not commonly used.
Given that crypt() has never been thread-safe, consider implementing
crypt_r() as in glibc and leaving crypt() thread-unsafe.
Thread-local storage via pthread_key_create() (one key for libcrypt) is
still "magic" but reduces the memory waste for threads that do not call
crypt().
> 5. includes a bunch of new test vectors for libcrypt ATF tests
OK.
Some remarks about the code:
lib/libcrypt/crypt.c crypt_makesalt()
> b64_from_24bit((uint8_t) rand_buf[2], (uint8_t) rand_buf[1], (uint8_t)
> rand_buf[0], diff, (int *) &(diff), &out);
All these casts can be avoided by making the affected variables the
proper type in the first place. The cast of &diff causes a
strict-aliasing violation and is definitely wrong on 64-bit big-endian
systems.
rand_buf is a salt, not a secret, so clearing it afterwards is
unnecessary.
Consider memcpy() and adding '\0' afterward instead of strncpy(). It
seems unnecessary to clear the buffer completely.
--
Jilles Tjoelker
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