linux-kernel - Re: GPF in keyring

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Date:	Mon, 19 Oct 2015 12:41:53 +0200
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	syzkaller@...glegroups.com
Cc:	David Howells <dhowells@...hat.com>, james.l.morris@...cle.com,
	serge@...lyn.com, keyrings@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Julien Tinnes <jln@...gle.com>, Kees Cook <keescook@...gle.com>
Subject: Re: GPF in keyring_destroy

On Mon, Oct 19, 2015 at 12:33 PM, David Howells <dhowells@...hat.com> wrote:
> Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
>> > Does the attached patch fix it for you?
>>
>> Yes, it fixes the crash for me.
>
> I have an additional patch to prevent keyrings from being constructed by
> request_key() at all (though it can still search for them).  Could you give
> this a spin in addition to the previous one also?

Do you mean in addition or instead of the previous one? From your
description, it sounds like it alone should prevent the crash.


> Thanks,
> David
> ---
> commit 27874345bb8d2c39f3d493607a86ecbfcb100405
> Author: David Howells <dhowells@...hat.com>
> Date:   Mon Oct 19 11:20:28 2015 +0100
>
>     KEYS: Don't permit request_key() to construct a new keyring
>
>     If request_key() is used to find a keyring, only do the search part - don't
>     do the construction part if the keyring was not found by the search.  We
>     don't really want keyrings in the negative instantiated state since the
>     rejected/negative instantiation error value in the payload is unioned with
>     keyring metadata.
>
>     Signed-off-by: David Howells <dhowells@...hat.com>
>
> diff --git a/security/keys/request_key.c b/security/keys/request_key.c
> index 486ef6fa393b..0d6253124278 100644
> --- a/security/keys/request_key.c
> +++ b/security/keys/request_key.c
> @@ -440,6 +440,9 @@ static struct key *construct_key_and_link(struct keyring_search_context *ctx,
>
>         kenter("");
>
> +       if (ctx->index_key.type == &key_type_keyring)
> +               return ERR_PTR(-EPERM);
> +
>         user = key_user_lookup(current_fsuid());
>         if (!user)
>                 return ERR_PTR(-ENOMEM);
>
> --
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