linux-kernel - Re: [PATCH v2] crypto: ccp - Fix the INIT

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Message-ID: <fe209f25-6119-cc26-2608-8aaccf11ac36@amd.com>
Date:   Fri, 15 Apr 2022 08:49:43 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Jacky Li <jackyli@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>,
        John Allen <john.allen@....com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Marc Orr <marcorr@...gle.com>, Alper Gun <alpergun@...gle.com>,
        Peter Gonda <pgonda@...gle.com>, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] crypto: ccp - Fix the INIT_EX data file open failure

On 4/14/22 11:23, Jacky Li wrote:
> There are 2 common cases when INIT_EX data file might not be
> opened successfully and fail the sev initialization:
> 
> 1. In user namespaces, normal user tasks (e.g. VMM) can change their
>     current->fs->root to point to arbitrary directories. While
>     init_ex_path is provided as a module param related to root file
>     system. Solution: use the root directory of init_task to avoid
>     accessing the wrong file.
> 
> 2. Normal user tasks (e.g. VMM) don't have the privilege to access
>     the INIT_EX data file. Solution: open the file as root and
>     restore permissions immediately.
> 
> Fixes: 3d725965f836 ("crypto: ccp - Add SEV_INIT_EX support")
> Signed-off-by: Jacky Li <jackyli@...gle.com>
> Reviewed-by: Peter Gonda <pgonda@...gle.com>

Looks good, just a quick question. Should there be any type of access 
checks before switching credentials? Should we check access to /dev/sev or 
such? Or is the capability to load the module enough?

Thanks,
Tom

> ---
> Changelog since v1:
> - Added Fixes tag and Reviewed-By tag.
> 
>   drivers/crypto/ccp/sev-dev.c | 30 ++++++++++++++++++++++++++++--
>   1 file changed, 28 insertions(+), 2 deletions(-)
>