Re: [PATCH v7 0/5] IMA: restrict the accepted digest algorithms for the security.ima xattr
Hello,
On Wednesday, August 11, 2021 3:40:51 PM EDT Mimi Zohar wrote:
On Wed, 2021-08-11 at 11:40 +0000, THOBY Simon wrote:
Other than the two questions on " IMA: add a policy option to restrict
xattr hash algorithms on appraisal" patch, the patch set is looking
good.
thanks,
Mimi
> Here is also a short description of the new audit messages, but I can
> send it in a followup mail if that is not the proper place:
>
> When writing the xattr with an algorithm not built in the kernel (here
> the
> kernel was built with CONFIG_CRYPTO_MD5 unset), e.g. with
>
> "evmctl ima_hash -a md5 /usr/bin/strace":
> audit(1628066120.418:121): pid=1344 uid=0 auid=0 ses=1
> subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 op=set_data
> cause=unavailable-hash-algorithm comm="evmctl"
name="/usr/bin/strace"
> dev="dm-0" ino=2632657 res=0 errno=0>
Is this audit event accurate? I seem to be seeing name=value=value. I'm
hoping this is a copy/paste/mail client issue.
-Steve
> With the same command and the policy rule
>
> "appraise func=SETXATTR_CHECK appraise_algos=sha256,sha384,sha512", we
get:
> audit(1628066210.141:127): pid=1362 uid=0 auid=0 ses=1
> subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 op=set_data
> cause=denied-hash-algorithm comm="evmctl"
name="/usr/bin/strace"
> dev="dm-0" ino=2632657 res=0 errno=0>
> Note that the cause is now 'denied-hash-algorithm' instead of
> 'unavailable-hash-algorithm'. We get that audit message for any algorithm
> outside of sha256/384/512 (including algorithms not compiled in the
> kernel
> like MD5). In a sense, 'denied-hash-algorithm' takes predecence over
> 'unavailable-hash-algorithm'.
>
> When appraising files, e.g. trying to execute a file whose xattr was
> hashed with sha1 while the policy rule
>
> "appraise func=BPRM_CHECK fowner=0 appraise_algos=sha256" is enabled:
> audit(1628066349.230:130): pid=1369 uid=0 auid=0 ses=1
> subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
> op=collect_data cause=denied-hash-algorithm comm="bash"
> name="/usr/bin/strace" dev="dm-0" ino=2632657 res=0 errno=0>
> This series is based on the following repo/branch:
> repo:
> https://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.g
> it branch: next-integrity-testing
> commit e37be5343ae2b9419aea1442b07e5d2428b437b4 ("Merge branch
> 'ima-buffer-measurement-changes-v4' into next-integrity")
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