linux-kernel - Re: d7be102f29 ("cfg80211: initialize regulatory keys/database later"): kernel BUG at crypto/asymmetric_keys/public

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Message-ID: <CAGXu5jJGsqXda7qviDpdMEo1moJDMJ8UMhC8VZh6Mkg6bsW+_A@mail.gmail.com>
Date:   Mon, 27 Nov 2017 15:30:27 -0800
From:   Kees Cook <keescook@...omium.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Josh Boyer <jwboyer@...hat.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Xiaolong Ye <xiaolong.ye@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, LKP <lkp@...org>
Subject: Re: d7be102f29 ("cfg80211: initialize regulatory keys/database
 later"): kernel BUG at crypto/asymmetric_keys/public_key.c:80!

On Mon, Nov 27, 2017 at 3:25 PM, David Howells <dhowells@...hat.com> wrote:
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>> I'm not seeing why it would ever be ok to do BUG_ON() instead of just
>> returning an error, though.
>
> This function has a list of requisite parameters for the caller:
>
>         BUG_ON(!pkey);          <-- You need the public key to use,
>         BUG_ON(!sig);
>         BUG_ON(!sig->digest);   <-- the message digest to check
>         BUG_ON(!sig->s);        <-- and you need the signature.
>
> If you fail to obtain any one of these parameters, you can't use this function
> and you should have errored out before calling this function.  It seems
> reasonable for the function to assume that you've provided them - they're kind
> of essential to the operation.  If you want, I can just remove the checks
> entirely.  Many of the kernel's functions don't perform argument checking, but
> just assume you've done it right and will oops if you haven't.
>
> I could just return -EINVAL, yes, but I'm not sure that's really the right
> thing to do, at least not without printing an error message, since it's a
> kernel programming error not a userspace error or data error.

The preference even in these cases has been to keep things recoverable
unless there is a very good reason to immediately stop the kernel's
thread of execution. If all callers already check for return values,
replacing BUG_ON() with WARN() and returning -EINVAL would be best.

-Kees

-- 
Kees Cook
Pixel Security