Re: [PATCH v12 04/26] ima: Move arch_policy_entry into ima_namespace

Serge E. Hallyn
2022-05-21T02:46:35Z

On Wed, Apr 20, 2022 at 10:06:11AM -0400, Stefan Berger wrote:
> The architecture-specific policy rules, currently defined for EFI and
> powerpc, require the kexec kernel image and kernel modules to be
> validly signed and measured, based on the system's secure boot and/or
> trusted boot mode and the IMA_ARCH_POLICY Kconfig option being enabled.
>
> To avoid special-casing init_ima_ns as much as possible, move the
> arch_policy_entry into the ima_namespace.
>
> When freeing the arch_policy_entry set the pointer to NULL.
>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> Acked-by: Christian Brauner <brauner@kernel.org>
> Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
> ---
> security/integrity/ima/ima.h | 3 +++
> security/integrity/ima/ima_init_ima_ns.c | 1 +
> security/integrity/ima/ima_policy.c | 23 +++++++++++------------
> 3 files changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 9bcde1a24e74..2305bf223a98 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -125,6 +125,9 @@ struct ima_namespace {
>
> struct list_head __rcu *ima_rules; /* Pointer to the current policy */
> int ima_policy_flag;
> +
> + /* An array of architecture specific rules */
> + struct ima_rule_entry *arch_policy_entry;
> } __randomize_layout;
> extern struct ima_namespace init_ima_ns;
>
> diff --git a/security/integrity/ima/ima_init_ima_ns.c b/security/integrity/ima/ima_init_ima_ns.c
> index c919a456b525..ae33621c3955 100644
> --- a/security/integrity/ima/ima_init_ima_ns.c
> +++ b/security/integrity/ima/ima_init_ima_ns.c
> @@ -15,6 +15,7 @@ static int ima_init_namespace(struct ima_namespace *ns)
> INIT_LIST_HEAD(&ns->ima_temp_rules);
> ns->ima_rules = (struct list_head __rcu *)(&ns->ima_default_rules);
> ns->ima_policy_flag = 0;
> + ns->arch_policy_entry = NULL;
>
> return 0;
> }
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 69b19f4d5fee..0a7c61ca3265 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -228,9 +228,6 @@ static struct ima_rule_entry critical_data_rules[] __ro_after_init = {
> {.action = MEASURE, .func = CRITICAL_DATA, .flags = IMA_FUNC},
> };
>
> -/* An array of architecture specific rules */
> -static struct ima_rule_entry *arch_policy_entry __ro_after_init;
> -
> static int ima_policy __initdata;
>
> static int __init default_measure_policy_setup(char *str)
> @@ -859,9 +856,10 @@ static int __init ima_init_arch_policy(struct ima_namespace *ns)
> for (rules = arch_rules; *rules != NULL; rules++)
> arch_entries++;
>
> - arch_policy_entry = kcalloc(arch_entries + 1,
> - sizeof(*arch_policy_entry), GFP_KERNEL);
> - if (!arch_policy_entry)
> + ns->arch_policy_entry = kcalloc(arch_entries + 1,
> + sizeof(*ns->arch_policy_entry),
> + GFP_KERNEL);
> + if (!ns->arch_policy_entry)
> return 0;
>
> /* Convert each policy string rules to struct ima_rule_entry format */
> @@ -871,13 +869,13 @@ static int __init ima_init_arch_policy(struct ima_namespace *ns)
>
> result = strscpy(rule, *rules, sizeof(rule));
>
> - INIT_LIST_HEAD(&arch_policy_entry[i].list);
> - result = ima_parse_rule(ns, rule, &arch_policy_entry[i]);
> + INIT_LIST_HEAD(&ns->arch_policy_entry[i].list);
> + result = ima_parse_rule(ns, rule, &ns->arch_policy_entry[i]);
> if (result) {
> pr_warn("Skipping unknown architecture policy rule: %s\n",
> rule);
> - memset(&arch_policy_entry[i], 0,
> - sizeof(*arch_policy_entry));
> + memset(&ns->arch_policy_entry[i], 0,
> + sizeof(ns->arch_policy_entry[i]));
> continue;
> }
> i++;
> @@ -925,7 +923,7 @@ void __init ima_init_policy(struct ima_namespace *ns)
> if (!arch_entries)
> pr_info("No architecture policies found\n");
> else
> - add_rules(ns, arch_policy_entry, arch_entries,
> + add_rules(ns, ns->arch_policy_entry, arch_entries,
> IMA_DEFAULT_POLICY | IMA_CUSTOM_POLICY);
>
> /*
> @@ -1005,7 +1003,8 @@ void ima_update_policy(struct ima_namespace *ns)
> * on boot. After loading a custom policy, free the
> * architecture specific rules stored as an array.
> */
> - kfree(arch_policy_entry);
> + kfree(ns->arch_policy_entry);
> + ns->arch_policy_entry = NULL;

So the thing that prevents multiple racing occurances of the above two lines is
that ima_open_policy() sets IMA_FS_BUSY (or returns EBUSY) and then removes
this file before clearing the flag, right?

Seems good.

Reviewed-by: Serge Hallyn <serge@hallyn.com>

> }
> ima_update_policy_flags(ns);
>
> --
> 2.34.1