ima: limit the builtin 'tcb' dont_measure tmpfs policy rule

With a custom policy similar to the builtin IMA 'tcb' policy [1], arch
specific policy, and a kexec boot command line measurement policy rule,
the kexec boot command line is not measured due to the dont_measure
tmpfs rule.

Limit the builtin 'tcb' dont_measure tmpfs policy rule to just the
"func=FILE_CHECK" hook.  Depending on the end users security threat
model, a custom policy might not even include this dont_measure tmpfs
rule.

Note: as a result of this policy rule change, other measurements might
also be included in the IMA-measurement list that previously weren't
included.

[1] https://ima-doc.readthedocs.io/en/latest/ima-policy.html#ima-tcb

Reviewed-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 21a8e54c383f08a9fc9e478f726cb9d1ab7f34a5..23bbe2c405f0188ec84d4d1c3b252dfa2b5530ae 100644 (file)
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -148,7 +148,8 @@ static struct ima_rule_entry dont_measure_rules[] __ro_after_init = {
        {.action = DONT_MEASURE, .fsmagic = PROC_SUPER_MAGIC, .flags = IMA_FSMAGIC},
        {.action = DONT_MEASURE, .fsmagic = SYSFS_MAGIC, .flags = IMA_FSMAGIC},
        {.action = DONT_MEASURE, .fsmagic = DEBUGFS_MAGIC, .flags = IMA_FSMAGIC},
-       {.action = DONT_MEASURE, .fsmagic = TMPFS_MAGIC, .flags = IMA_FSMAGIC},
+       {.action = DONT_MEASURE, .fsmagic = TMPFS_MAGIC, .func = FILE_CHECK,
+        .flags = IMA_FSMAGIC | IMA_FUNC},
        {.action = DONT_MEASURE, .fsmagic = DEVPTS_SUPER_MAGIC, .flags = IMA_FSMAGIC},
        {.action = DONT_MEASURE, .fsmagic = BINFMTFS_MAGIC, .flags = IMA_FSMAGIC},
        {.action = DONT_MEASURE, .fsmagic = SECURITYFS_MAGIC, .flags = IMA_FSMAGIC},