On Thu, 2024-06-20 at 10:48 -0400, Paul Moore wrote:

On Thu, Jun 20, 2024 at 5:12 AM Roberto Sassu
[off-list ref] wrote:

quoted

On Wed, 2024-06-19 at 14:43 -0400, Paul Moore wrote:

quoted

On Wed, Jun 19, 2024 at 12:38 PM Roberto Sassu
[off-list ref] wrote:

quoted

Making it a kernel subsystem would likely mean replicating what the LSM
infrastructure is doing, inode (security) blob and being notified about
file/directory changes.

Just because the LSM framework can be used for something, perhaps it
even makes the implementation easier, it doesn't mean the framework
should be used for everything.

It is supporting 3 LSMs: IMA, IPE and BPF LSM.

That makes it a clear target for the security subsystem, and as you
suggested to start for IMA, if other kernel subsystems require them, we
can make it as an independent subsystem.

Have you discussed the file digest cache functionality with either the
IPE or BPF LSM maintainers?  While digest_cache may support these

Well, yes. I was in a discussion since long time ago with Deven and
Fan. The digest_cache LSM is listed in the Use Case section of the IPE
cover letter:

https://lore.kernel.org/linux-integrity/1716583609-21790-1-git-send-email-wufan@linux.microsoft.com/ (local)

I also developed an IPE module back in the DIGLIM days:

https://lore.kernel.org/linux-integrity/a16a628b9e21433198c490500a987121@huawei.com/ (local)

As for eBPF, I just need to make the digest_cache LSM API callable by
eBPF programs, very likely not requiring any change on the eBPF
infrastructure itself. As an example of the modification needed, you
could have a look at:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/trace/bpf_trace.c?h=v6.10-rc4#n1381


Once the digest_cache LSM API is exposed in eBPF, you could write a
simple file integrity check (taken from my DIGLIM eBPF), not tested:

SEC("lsm.s/bprm_creds_for_exec")
int BPF_PROG(exec, struct linux_binprm *bprm)
{
	u8 digest[MAX_DIGEST_SIZE] = { 0 };
	digest_cache_found_t found;
	struct digest_cache;
	int algo;

	algo = bpf_ima_file_hash(bprm->file, digest, sizeof(digest));
	if (algo < 0)
		return -EPERM;

	digest_cache = bpf_digest_cache_get(bprm->file->f_path.dentry);
	if (!digest_cache)
		return -EPERM;

	found = bpf_digest_cache_lookup(bprm->file->f_path.dentry,
					digest_cache, digest, algo);

	bpf_digest_cache_put(digest_cache);
	return found ? 0 : -EPERM;
}

Roberto

LSMs, I don't recall seeing any comments from the other LSM
developers; if you are going to advocate for this as something outside
of IMA, it would be good to see a show of support for the other LSMs.