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f1e10b1087
When a signed policy is not mandatory, userspace can write IMA policy rules
directly to the securityfs policy file:
echo -e "measure func=BPRM_CHECK mask=MAY_EXEC\n" \
"audit func=BPRM_CHECK mask=MAY_EXEC\n" \
> /sys/kernel/security/ima/policy
or by cat'ing the entire IMA custom policy file:
cat ima-policy-file > /sys/kernel/security/ima/policy
Because these rules originate from userspace and cross the userspace/kernel
trust boundary, measure the raw write buffer before parsing, regardless of
whether the new policy will be accepted or not. This can be caught when
'measure func=POLICY_CHECK' is enabled (e.g., ima_policy=tcb). The
measurement template is forced to ima-buf.
This follows the "measure & load" paradigm, exposing potential bugs in
the policy code and detecting attempts to corrupt IMA. It also completes
the POLICY_CHECK hook, which already measures partial policy load by file.
To verify the template data hash value, convert the buffer policy data
to binary:
grep "ima_policy_written" \
/sys/kernel/security/integrity/ima/ascii_runtime_measurements | \
tail -1 | cut -d' ' -f 6 | xxd -r -p | sha256sum
Suggested-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Enrico Bravi <enrico.bravi@polito.it>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
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|---|---|---|
| .. | ||
| ima_api.c | ||
| ima_appraise.c | ||
| ima_asymmetric_keys.c | ||
| ima_crypto.c | ||
| ima_efi.c | ||
| ima_fs.c | ||
| ima_iint.c | ||
| ima_init.c | ||
| ima_kexec.c | ||
| ima_main.c | ||
| ima_modsig.c | ||
| ima_mok.c | ||
| ima_policy.c | ||
| ima_queue_keys.c | ||
| ima_queue.c | ||
| ima_template_lib.c | ||
| ima_template_lib.h | ||
| ima_template.c | ||
| ima.h | ||
| Kconfig | ||
| Makefile | ||