Re: [PATCH 0/2] support to read and tune appraise mode in runtime

[Tianjia Zhang <tianjia.zhang@linux.alibaba.com>]

On 2020/4/14 5:55, Mimi Zohar wrote:
> On Thu, 2020-04-09 at 11:39 +0800, Tianjia Zhang wrote:
>> Support the read and write operations of ima_appraise by adding a
>> securifyfs file 'appraise_mode'.
>>
>> In order to tune appraise mode in runtime, writing a PKCS#7 signature
>> corresponding the signed content is required. The content should be off,
>> enforce, log or fix. Given a simple way to archive this:
>>
>> $ echo -n off > mode
>> $ openssl smime -sign -nocerts -noattr -binary \
>>      -in mode -inkey <system_trusted_key> \
>>      -signer <cert> -outform der -out mode.p7s
>> $ sudo cat mode.p7s \
>>      > /sys/kernel/security/ima/appraise_mode
>>
>> Note that the signing key must be a trust key located in
>> system trusted keyring. So even the root privilege cannot
>> simply disable the enforcement.
> 
> There are major problems with disabling IMA appraisal.  This patch set
> proposes disabling IMA appraisal without even providing the motivation
> for such support.
> 
> A lot of effort went into preventing custom IMA policies from
> disabling appraising the kexec or kernel module signatures.  In
> addition, the "lockdown" patch set was upstreamed permitting IMA
> signature verification.  This patch set would break both of these
> features.
> 
> IMA relies on its own keyring for verifying file signatures, not the
> builtin or secondary trusted kernel keyrings.
> 
> Two methods already exist - xattr and appended signatures - for
> verifying file signatures.  This patch set assumes creating and
> signing a file, which is then written to a securityfs file.  Like for
> loading a custom IMA policy, instead of cat'ing the file, write the
> pathname to the securityfs file.
> 
> If you must define a new IMA method for verifying file signatures,
> then it needs to be generic and added to ima_appraise_measurement().
>   (Refer to the new IMA appended signature support.)
> 
> Mimi
> 
>>
>> Tianjia Zhang (2):
>>    ima: support to read appraise mode
>>    ima: support to tune appraise mode in runtime
>>
>>   security/integrity/ima/ima_fs.c | 134 +++++++++++++++++++++++++++++++-
>>   1 file changed, 133 insertions(+), 1 deletion(-)
>>

Thanks for your suggestion, the way to close the appraise mode here is 
indeed a bit rude, I will reconsider again according to your suggestions.

In addition, [PATCH 1/2] ima: support to read appraise mode, by the way, 
see if this patch is acceptable.

Thanks and best,
Tianjia