linux-kernel - Re: [RFC PATCH v4 05/12] fs: add security blob and hooks for block

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Date:   Mon, 20 Jul 2020 09:42:05 -0700
From:   Deven Bowers <deven.desai@...ux.microsoft.com>
To:     Casey Schaufler <casey@...aufler-ca.com>, agk@...hat.com,
        axboe@...nel.dk, snitzer@...hat.com, jmorris@...ei.org,
        serge@...lyn.com, zohar@...ux.ibm.com, viro@...iv.linux.org.uk,
        paul@...l-moore.com, eparis@...hat.com, jannh@...gle.com,
        dm-devel@...hat.com, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-audit@...hat.com
Cc:     tyhicks@...ux.microsoft.com, linux-kernel@...r.kernel.org,
        corbet@....net, sashal@...nel.org,
        jaskarankhurana@...ux.microsoft.com, mdsakib@...rosoft.com,
        nramas@...ux.microsoft.com
Subject: Re: [RFC PATCH v4 05/12] fs: add security blob and hooks for
 block_device



On 7/17/2020 5:14 PM, Casey Schaufler wrote:

[...snip]

>> +EXPORT_SYMBOL(security_bdev_free);
>> +
>> +int security_bdev_setsecurity(struct block_device *bdev,
>> +			      const char *name, const void *value,
>> +			      size_t size)
>> +{
>> +	return call_int_hook(bdev_setsecurity, 0, bdev, name, value, size);
>> +}
> 
> What is your expectation regarding multiple security modules using the
> same @name? What do you expect a security module to do if it does not
> support a particular @name? You may have a case where SELinux supports
> a @name that AppArmor (or KSRI) doesn't. -ENOSYS may be you friend here.
> 

I expect that some security modules may want to use the same @name / use
the data contained with @name. I cannot speak to the future cases of
other LSMs, but I expect if they want the raw @value, they'll copy it
into their security blob, or interpret @value to a field defined by
their security blob.

Originally, I expected a security module that does not implement a
particular @name no-op with return 0, not -ENOSYS, but I recognize that
error codes are valuable, and it's a trivial change - I'll switch the 
security hook to call the hooks while allowing -ENOSYS or 0 in the next 
iteration.

>> +EXPORT_SYMBOL(security_bdev_setsecurity);
>> +
>>   #ifdef CONFIG_PERF_EVENTS
>>   int security_perf_event_open(struct perf_event_attr *attr, int type)
>>   {