Re: [PATCH v4 1/2] security: add fault injection capability

[Alexander Potapenko]

On Wed, Nov 11, 2020 at 11:45 AM Aleksandr Nogikh <a.nogikh@xxxxxxxxx> wrote:
>
> From: Aleksandr Nogikh <nogikh@xxxxxxxxxx>
>
> Add a fault injection capability to call_int_hook macro. This will
> facilitate testing of fault tolerance of the code that invokes
> security hooks as well as the fault tolerance of the LSM
> implementations themselves.
>
> Add a KConfig option (CONFIG_FAIL_LSM_HOOKS) that controls whether the
> capability is enabled. In order to enable configuration from the user
> space, add the standard debugfs entries for fault injection (if
> CONFIG_FAULT_INJECTION_DEBUG_FS is enabled).
>
> Signed-off-by: Aleksandr Nogikh <nogikh@xxxxxxxxxx>
> Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
> Reviewed-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>

> ---
> v4:
> - Changed retval debugfs file type - now it keeps a signed integer.
> - Made CONFIG_FAIL_LSM_HOOKS depend on CONFIG_SECURITY.
> v2:
> - Renamed should_fail_lsm_hook() to lsm_hooks_inject_fail().
> ---
>  lib/Kconfig.debug   |  6 ++++
>  security/security.c | 69 +++++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 72 insertions(+), 3 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 6140413174be..5f4399816019 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1813,6 +1813,12 @@ config FAIL_MAKE_REQUEST
>         help
>           Provide fault-injection capability for disk IO.
>
> +config FAIL_LSM_HOOKS
> +       bool "Fault-injection capability for LSM hooks"
> +       depends on FAULT_INJECTION && SECURITY
> +       help
> +         Provide fault-injection capability for LSM hooks.
> +
>  config FAIL_IO_TIMEOUT
>         bool "Fault-injection capability for faking disk interrupts"
>         depends on FAULT_INJECTION && BLOCK
> diff --git a/security/security.c b/security/security.c
> index 69ff6e2e2cd4..be3a3c7c6d6a 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -28,6 +28,7 @@
>  #include <linux/backing-dev.h>
>  #include <linux/string.h>
>  #include <linux/msg.h>
> +#include <linux/fault-inject.h>
>  #include <net/flow.h>
>
>  #define MAX_LSM_EVM_XATTR      2
> @@ -669,6 +670,67 @@ static void __init lsm_early_task(struct task_struct *task)
>                 panic("%s: Early task alloc failed.\n", __func__);
>  }
>
> +
> +#ifdef CONFIG_FAIL_LSM_HOOKS
> +
> +static struct {
> +       struct fault_attr attr;
> +       int retval;
> +} fail_lsm_hooks = {
> +       .attr = FAULT_ATTR_INITIALIZER,
> +       .retval = -EACCES
> +};
> +
> +static int __init setup_fail_lsm_hooks(char *str)
> +{
> +       return setup_fault_attr(&fail_lsm_hooks.attr, str);
> +}
> +__setup("fail_lsm_hooks=", setup_fail_lsm_hooks);
> +
> +static int lsm_hooks_inject_fail(void)
> +{
> +       return should_fail(&fail_lsm_hooks.attr, 1) ? fail_lsm_hooks.retval : 0;
> +}
> +
> +#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
> +
> +static int fail_lsm_retval_set(void *data, u64 val)
> +{
> +       fail_lsm_hooks.retval = (int)val;
> +       return 0;
> +}
> +
> +static int fail_lsm_retval_get(void *data, u64 *val)
> +{
> +       *val = (u64)fail_lsm_hooks.retval;
> +       return 0;
> +}
> +
> +DEFINE_DEBUGFS_ATTRIBUTE(fail_lsm_retval_ops, fail_lsm_retval_get,
> +                                                fail_lsm_retval_set, "%lld\n");
> +
> +static int __init fail_lsm_hooks_debugfs(void)
> +{
> +       umode_t mode = S_IFREG | 0600;
> +       struct dentry *dir;
> +
> +       dir = fault_create_debugfs_attr("fail_lsm_hooks", NULL,
> +                                       &fail_lsm_hooks.attr);
> +       debugfs_create_file("retval", mode, dir, NULL,
> +                                               &fail_lsm_retval_ops);
> +       return 0;
> +}
> +
> +late_initcall(fail_lsm_hooks_debugfs);
> +
> +#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
> +
> +#else
> +
> +static inline int lsm_hooks_inject_fail(void) { return 0; }
> +
> +#endif /* CONFIG_FAIL_LSM_HOOKS */
> +
>  /*
>   * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
>   * can be accessed with:
> @@ -707,16 +769,17 @@ static void __init lsm_early_task(struct task_struct *task)
>         } while (0)
>
>  #define call_int_hook(FUNC, IRC, ...) ({                       \
> -       int RC = IRC;                                           \
> -       do {                                                    \
> +       int RC = lsm_hooks_inject_fail();                       \
> +       if (RC == 0) {                                                          \
>                 struct security_hook_list *P;                   \
> +               RC = IRC;                                                               \
>                                                                 \
>                 hlist_for_each_entry(P, &security_hook_heads.FUNC, list) { \
>                         RC = P->hook.FUNC(__VA_ARGS__);         \
>                         if (RC != 0)                            \
>                                 break;                          \
>                 }                                               \
> -       } while (0);                                            \
> +       }                                                       \
>         RC;                                                     \
>  })
>
> --
> 2.29.2.222.g5d2a92d10f8-goog
>


-- 
Alexander Potapenko
Software Engineer

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