[patch] libcrypt & friends - modular crypt format support in /etc/login.conf

[John-Mark Gurney]

Jilles Tjoelker wrote this message on Sun, Feb 15, 2015 at 00:17 +0100:
> On Tue, Feb 10, 2015 at 07:26:07AM -0500, Derek (freebsd lists) wrote:
> > 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.

It shouldn't be hard to support crypt_{get,set}_format, since default
is supported for find_format...

As for login_getcryptfmt, I can't find it...

and if we keep crypt_{get,set}_format, we can keep login_setcryptfmt,
but just mark them as deprecated...

> > 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.

And not linked against normally, so, I don't see an issue...

> Given that crypt() has never been thread-safe, consider implementing
> crypt_r() as in glibc and leaving crypt() thread-unsafe.

We should go full thread safe, though that requirese some work on most
of the functions, as it appears that only sha256 and sha512 are safe...

> 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().

With the way the crypt is pluggable, sharing storage between 
implementations doesn't seem doable...

Also, I just realized that crypt_sha256 and crypt_sha512 are not safe
in their use of __thread...  As the buffer isn't static, if the same
thread calls again, it could be previously returns memory gets free'd
by the realloc call...  

> 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.

I had thought of both of these before, and agree that the salt is not
a secret (it is kept hidden), but, it leaks information, and _makesalt
is called so rarely, that saving the time doesn't make sense...

So, I'd prefer to keep the code as is WRT these points..

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."