Re: [PATCH v8 7/8] ima: check against blacklisted hashes for files with modsig

On Sun, 2019-10-20 at 12:06 -0400, Mimi Zohar wrote:

On Sat, 2019-10-19 at 14:06 -0400, Nayna Jain wrote:

quoted

Asymmetric private keys are used to sign multiple files. The kernel
currently support checking against blacklisted keys. However, if the
public key is blacklisted, any file signed by the blacklisted key will
automatically fail signature verification. We might not want to blacklist
all the files signed by a particular key, but just a single file.
Blacklisting the public key is not fine enough granularity.

This patch adds support for checking against the blacklisted hash of the
file based on the IMA policy. The blacklisted hash is the file hash
without the appended signature. Defined is a new policy option
"appraise_flag=check_blacklist".

Please add an example of how to blacklist a file with an appended
signature.  The simplest example that works on x86 as well as Power
would be blacklisting a kernel module.  The example should include
calculating the kernel module hash without the appended signature,
enabling the Kconfig option (CONFIG_SYSTEM_BLACKLIST_HASH_LIST), and
the blacklist hash format (eg. "bin:<file hash>").

And of course, the IMA appraise kernel module policy rule containing
"appraise_flag=check_blacklist".

thanks,

Mimi