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56 lines
2.2 KiB
Markdown
56 lines
2.2 KiB
Markdown
## IMA
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IMA stands for Integrity Management Architecture. The basic idea is to prevent
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userspace from even *opening* files that have been mutated, by tracking file
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content via a hash in the `security.ima` extended attribute. IMA supports
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keeping track of these hashes and signing the result via the TPM, and a host of
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other features.
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Today, this is not namespace aware, so there is no way to differentiate in
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IMA's appraisal output between files in one mount namespace vs another, which
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makes this not particularly useful for container engines. The goal of this
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patchset is to make IMA namespace aware.
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## IMA namespace patches
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These are draft patches for an implementation of IMA namespacing. They are
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currently a rebased version of the v1 set posted here [1].
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### Usage
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Let's suppose you have some sensitive files owned by a particular user that you
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want to keep secure:
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sensitive=/tmp/foo
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user=71452
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mkdir -p $(dirname $sensitive) && echo "hello" > $sensitive
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chown $user $sensitive
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To use IMA in the per-namespace mode, you need ima\_appraise=enforce\_ns on the
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kernel CLI (this is done in the yaml file). Then, the userspace interface looks
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something like this:
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# create a new mount namespace
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unshare -m
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# enable per-ns policy for this new namespace
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nsid=$(readlink /proc/self/ns/mnt | cut -c '6-15')
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echo ${nsid} > /sys/kernel/security/ima/namespaces
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# set the policy (we use tmpfs magic here since that's all that linuxkit
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# has available to write to for this example)
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TMPFS_MAGIC=0x01021994
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printf "appraise fsmagic=$TMPFS_MAGIC fowner=$user\nappraise func=MODULE_CHECK" > /sys/kernel/security/ima/$nsid/policy
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hash=$(echo -e "\x4$(openssl dgst -sha256 -binary $sensitive)")
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setfattr -n security.ima -v "${hash}" $sensitive
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And now you should be able to see things failing:
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moby:/# echo foo > /tmp/foo
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moby:/# cat /tmp/foo
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[ 3233.681544] audit: type=1800 audit(1495131746.610:29): pid=384 uid=0 auid=4294967295 ses=4294967295 op="appraise_data" cause="invalid-hash" comm="cat" name="/tmp/foo" mnt_ns=4026532208 dev="tmpfs" ino=13105 res=0
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cat: can't open '/tmp/foo': Permission denied
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[1]: https://lkml.org/lkml/2017/5/11/699
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