linux-kernel - Re: GPF in keyring

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Message-ID: <17443.1445250818@warthog.procyon.org.uk>
Date:	Mon, 19 Oct 2015 11:33:38 +0100
From:	David Howells <dhowells@...hat.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	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>, syzkaller@...glegroups.com,
	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

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?

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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