Re: [PATCH v4 8/8] module: replace the existing LSM hook in init_module

[Paul Moore]

On Tue, May 29, 2018 at 2:02 PM, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> Both the init_module and finit_module syscalls call either directly
> or indirectly the security_kernel_read_file LSM hook.  This patch
> replaces the direct call in init_module with a call to the new
> security_kernel_load_data hook and makes the corresponding changes in
> SELinux and IMA.
>
> Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> Cc: Jeff Vander Stoep <jeffv@xxxxxxxxxx>
> Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
> Cc: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> ---
>  kernel/module.c                   |  2 +-
>  security/integrity/ima/ima_main.c | 24 ++++++++++--------------
>  security/selinux/hooks.c          | 26 ++++++++++++++++++++------
>  3 files changed, 31 insertions(+), 21 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index ce8066b88178..b97c642b5b4d 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2879,7 +2879,7 @@ static int copy_module_from_user(const void __user *umod, unsigned long len,
>         if (info->len < sizeof(*(info->hdr)))
>                 return -ENOEXEC;
>
> -       err = security_kernel_read_file(NULL, READING_MODULE);
> +       err = security_kernel_load_data(LOADING_MODULE);
>         if (err)
>                 return err;
>
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 3dae605a1604..0ff1d8152f6e 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -441,17 +441,6 @@ static int read_idmap[READING_MAX_ID] = {
>   */
>  int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
>  {
> -       bool sig_enforce = is_module_sig_enforced();
> -
> -       if (!file && read_id == READING_MODULE) {
> -               if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES) &&
> -                   (ima_appraise & IMA_APPRAISE_ENFORCE)) {
> -                       pr_err("impossible to appraise a module without a file descriptor. sig_enforce kernel parameter might help\n");
> -                       return -EACCES; /* INTEGRITY_UNKNOWN */
> -               }
> -               return 0;       /* We rely on module signature checking */
> -       }
> -
>         if (read_id == READING_FIRMWARE_PREALLOC_BUFFER) {
>                 if ((ima_appraise & IMA_APPRAISE_FIRMWARE) &&
>                     (ima_appraise & IMA_APPRAISE_ENFORCE)) {
> @@ -490,9 +479,6 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
>                 return 0;
>         }
>
> -       if (!file && read_id == READING_MODULE) /* MODULE_SIG_FORCE enabled */
> -               return 0;
> -
>         /* permit signed certs */
>         if (!file && read_id == READING_X509_CERTIFICATE)
>                 return 0;
> @@ -521,6 +507,8 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
>   */
>  int ima_load_data(enum kernel_load_data_id id)
>  {
> +       bool sig_enforce;
> +
>         if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
>                 return 0;
>
> @@ -536,6 +524,14 @@ int ima_load_data(enum kernel_load_data_id id)
>                         pr_err("Prevent firmware sysfs fallback loading.\n");
>                         return -EACCES; /* INTEGRITY_UNKNOWN */
>                 }
> +               break;
> +       case LOADING_MODULE:
> +               sig_enforce = is_module_sig_enforced();
> +
> +               if (!sig_enforce && (ima_appraise & IMA_APPRAISE_MODULES)) {
> +                       pr_err("impossible to appraise a module without a file descriptor. sig_enforce kernel parameter might help\n");
> +                       return -EACCES; /* INTEGRITY_UNKNOWN */
> +               }
>         default:
>                 break;
>         }
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 02ebd1585eaf..e02186470fc5 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -4018,12 +4018,6 @@ static int selinux_kernel_module_from_file(struct file *file)
>         u32 sid = current_sid();
>         int rc;
>
> -       /* init_module */
> -       if (file == NULL)
> -               return avc_has_perm(&selinux_state,
> -                                   sid, sid, SECCLASS_SYSTEM,
> -                                       SYSTEM__MODULE_LOAD, NULL);
> -
>         /* finit_module */
>
>         ad.type = LSM_AUDIT_DATA_FILE;
> @@ -4043,6 +4037,25 @@ static int selinux_kernel_module_from_file(struct file *file)
>                                 SYSTEM__MODULE_LOAD, &ad);
>  }
>
> +static int selinux_kernel_load_data(enum kernel_load_data_id id)
> +{
> +       u32 sid;
> +       int rc = 0;
> +
> +       switch (id) {
> +       case LOADING_MODULE:
> +               sid = current_sid();
> +
> +               /* init_module */
> +               return avc_has_perm(&selinux_state, sid, sid, SECCLASS_SYSTEM,
> +                                   SYSTEM__MODULE_LOAD, NULL);
> +       default:
> +               break;
> +       }
> +
> +       return rc;
> +}

I'm not a fan of the duplication here.  If we must have a new LSM hook
for this, can we at least have it call
selinux_kernel_module_from_file() so we have all the kernel module
loading logic/controls in one function?  Yes, I understand there are
differences between init_module() and finit_module() but I like
handling them both in one function as we do today.

>  static int selinux_kernel_read_file(struct file *file,
>                                     enum kernel_read_file_id id)
>  {
> @@ -6950,6 +6963,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
>         LSM_HOOK_INIT(kernel_act_as, selinux_kernel_act_as),
>         LSM_HOOK_INIT(kernel_create_files_as, selinux_kernel_create_files_as),
>         LSM_HOOK_INIT(kernel_module_request, selinux_kernel_module_request),
> +       LSM_HOOK_INIT(kernel_load_data, selinux_kernel_load_data),
>         LSM_HOOK_INIT(kernel_read_file, selinux_kernel_read_file),
>         LSM_HOOK_INIT(task_setpgid, selinux_task_setpgid),
>         LSM_HOOK_INIT(task_getpgid, selinux_task_getpgid),
> --
> 2.7.5
>

-- 
paul moore
www.paul-moore.com