Re: [PATCH] ima: limit the builtin 'tcb' dont_measure tmpfs policy rule

[Petr Vorel <pvorel@suse.cz>]

Hi Mimi,

> 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.

LGTM.
Reviewed-by: Petr Vorel <pvorel@suse.cz>

Kind regards,
Petr

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

> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
>  security/integrity/ima/ima_policy.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 21a8e54c383f..23bbe2c405f0 100644
> --- 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},