[RFC][PATCH 1/3] evm: Move hooks outside LSM infrastructure
zohar at linux.ibm.com
Fri May 8 17:08:04 UTC 2020
On Fri, 2020-05-08 at 10:20 +0000, Roberto Sassu wrote:
> > From: Mimi Zohar [mailto:zohar at linux.ibm.com]
> > On Thu, 2020-05-07 at 16:47 +0000, Roberto Sassu wrote:
> > > > the file metadata to the file data. The IMA and EVM policies really
> > > > need to be in sync.
> > >
> > > It would be nice, but at the moment EVM considers also files that are
> > > not selected by the IMA policy. An example of why this is a problem is
> > > the audit service that fails to start when it tries to adjust the permissions
> > > of the log files. Those files don't have security.evm because they are
> > > not appraised by IMA, but EVM denies the operation.
> > No, this is a timing issue as to whether or not the builtin policy or
> > a custom policy has been loaded. A custom policy could exclude the
> > log files based on LSM labels, but they are included in the builtin
> > policy.
> Yes, I was referring to a custom policy. In this case, EVM will not adapt
> to the custom policy but still verifies all files. If access control is done
> exclusively by IMA at the time evm_verifyxattr() is called, we wouldn't
> need to add security.evm to all files.
Roberto, EVM is only triggered by IMA, unless you've modified the
kernel to do otherwise.
I'm not interested in a complicated solution, just one that addresses
the new EVM immutable and portable signature. It might require EVM
HMAC, IMA differentiating between a new file and an existing file, or
it might require writing the new EVM signature last, after all the
other xattrs or metadata are updated. Please nothing that changes
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