linux-kernel - Re: [PATCH v2 2/2] KEYS: Avoid false positive ENOMEM error on key read

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Message-ID: <7d0b0c5f-98e7-0fb6-69cd-76a31a010bcb@redhat.com>
Date:   Wed, 11 Mar 2020 11:33:54 -0400
From:   Waiman Long <longman@...hat.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Mimi Zohar <zohar@...ux.ibm.com>, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Chris von Recklinghausen <crecklin@...hat.com>
Subject: Re: [PATCH v2 2/2] KEYS: Avoid false positive ENOMEM error on key
 read

On 3/10/20 1:12 PM, David Howells wrote:
> Waiman Long <longman@...hat.com> wrote:
>
>> That is not as simple as I thought. First of that, there is not an
>> equivalent kzvfree() helper to clear the buffer first before clearing.
>> Of course, I can do that manually.
> Yeah, the actual substance of vfree() may get deferred.  It may be worth
> adding a kvzfree() that switches between kzfree() and memset(),vfree().
>
>> With patch 2, the allocated buffer length will be max(1024, keylen). The
>> security code uses kmalloc() for allocation. If we use kvalloc() here,
>> perhaps we should also use that for allocation that can be potentially
>> large like that in big_key. What do you think?
> Not for big_key: if it's larger than BIG_KEY_FILE_THRESHOLD (~1KiB) it gets
> written encrypted into shmem so that it can be swapped out to disk when not in
> use.
>
> However, other cases, sure - just be aware that on a 32-bit system,
> vmalloc/vmap space is a strictly limited resource.

Attached is an additional patch to make the transition from kmalloc() to
kvmalloc(). I put the __kvzfree() helper in internal.h for now. I plan
to send a patch later to add a kvzfree() API once there is a use case in
the kernel.

I am not going to touch other places for now to make thing simpler.

Cheers,
Longman


View attachment "v2-0003-KEYS-Use-kvmalloc-to-better-handle-large-buffer-a.patch" of type "text/x-patch" (2956 bytes)