On 09/24/2018 05:18 PM, Kees Cook wrote:
> Before now, all the LSMs that did not specify an "enable" variable in their
> struct lsm_info were considered enabled by default. This prepares to make
> LSM enabling more explicit. For all LSMs without an explicit "enable"
> variable, a hard-coded storage location is chosen, and all LSMs without
> an external "enable" state have their state explicitly set to "enabled".
>
> This code appears more complex than it needs to be (comma-separated
> list parsing and "set" function parameter) because its use will be
> expanded on in the following patches to provide more explicit enabling.
>
> Signed-off-by: Kees Cook <keesc...@chromium.org>
Reviewed-by: John Johansen <john.johan...@canonical.com>
> ---
> security/security.c | 69 ++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 65 insertions(+), 4 deletions(-)
>
> diff --git a/security/security.c b/security/security.c
> index 056b36cf6245..a8107d54b3d3 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -54,17 +54,46 @@ static bool debug __initdata;
>
> static bool __init is_enabled(struct lsm_info *lsm)
> {
> - if (!lsm->enabled || *lsm->enabled)
> - return true;
> + if (WARN_ON(!lsm->enabled))
> + return false;
>
> - return false;
> + return *lsm->enabled;
> }
>
> /* Mark an LSM's enabled flag, if it exists. */
> -static void __init set_enabled(struct lsm_info *lsm, bool enabled)
> +static int lsm_enabled_true __initdata = 1;
> +static int lsm_enabled_false __initdata = 0;
> +
> +static void __init default_enabled(struct lsm_info *lsm, bool enabled)
> {
> + /* If storage location already set, skip this one. */
> if (lsm->enabled)
> + return;
> +
> + /*
> + * When an LSM hasn't configured an enable variable, we can use
> + * a hard-coded location for storing the default enabled state.
> + */
> + if (enabled)
> + lsm->enabled = &lsm_enabled_true;
> + else
> + lsm->enabled = &lsm_enabled_false;
> +}
> +
> +static void __init set_enabled(struct lsm_info *lsm, bool enabled)
> +{
> + if (WARN_ON(!lsm->enabled))
> + return;
> +
> + if (lsm->enabled == &lsm_enabled_true) {
> + if (!enabled)
> + lsm->enabled = &lsm_enabled_false;
> + } else if (lsm->enabled == &lsm_enabled_false) {
> + if (enabled)
> + lsm->enabled = &lsm_enabled_true;
> + } else {
> *lsm->enabled = enabled;
> + }
> }
>
> /* Is an LSM allowed to be initialized? */
> @@ -127,6 +156,35 @@ static void __init major_lsm_init(void)
> }
> }
>
> +static void __init parse_lsm_enable(const char *str,
> + void (*set)(struct lsm_info *, bool),
> + bool enabled)
> +{
> + char *sep, *name, *next;
> +
> + if (!str)
> + return;
> +
> + sep = kstrdup(str, GFP_KERNEL);
> + next = sep;
> + while ((name = strsep(&next, ",")) != NULL) {
> + struct lsm_info *lsm;
> +
> + for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
> + if (strcmp(name, "all") == 0 ||
> + strcmp(name, lsm->name) == 0)
> + set(lsm, enabled);
> + }
> + }
> + kfree(sep);
> +}
> +
> +static void __init prepare_lsm_enable(void)
> +{
> + /* Prepare defaults. */
> + parse_lsm_enable("all", default_enabled, true);
> +}
> +
> /**
> * security_init - initializes the security framework
> *
> @@ -143,6 +201,9 @@ int __init security_init(void)
> i++)
> INIT_HLIST_HEAD(&list[i]);
>
> + /* Figure out which LSMs are enabled and disabled. */
> + prepare_lsm_enable();
> +
> /*
> * Load minor LSMs, with the capability module always first.
> */
>
