Re: [PATCH] crypt_blowfish: allow short salt strings

[Solar Designer <solar@openwall.com>]

On Sun, Mar 27, 2016 at 05:11:21AM +0300, Solar Designer wrote:
> There is one maybe-bug seen in your test results: the "*" return on
> error.  Normally, it would be "*0" or "*1" for crypt_blowfish, and it
> would never match the salt input.  Rich, did musl retain this behavior?
> Where does the bare "*" come from?  The concern here is that a "*" might
> also be returned when crypt() is called with "*" for the salt input.
> Then its output would match what may be a stored hash placeholder, where
> "*" means locked account or an error having occurred when the password
> was set.  We must deny access in such cases, but returning "*" on all
> errors would grant access.  This could be a musl or PHP security bug, if
> it's indeed as bad as it appears from that test.

I just discussed this with Rich.

Yes, musl's modified crypt_blowfish returns "*" on error.  No, this
isn't a security bug in musl as a whole, because that code path is not
reached when the setting argument is "*" as well.  So no match.

However, there's risk for code reuse from musl by other projects, and
for potential cut-down revisions of musl (with only bcrypt left, invoked
unconditionally).  So I think a change is needed, either reintroducing
the "*0" / "*1" behavior (my preference) or returning NULL (Rich's
preference) on error like glibc does (and unfortunately crashing older
programs that don't expect this).

Alexander