Re: [PATCH v15 04/23] LSM: Use lsmblob in security_kernel_act_as

[Paul Moore <paul@paul-moore.com>]

On Fri, Feb 14, 2020 at 6:42 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>
> Change the security_kernel_act_as interface to use a lsmblob
> structure in place of the single u32 secid in support of
> module stacking. Change its only caller, set_security_override,
> to do the same. Change that one's only caller,
> set_security_override_from_ctx, to call it with the new
> parameter type.
>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: John Johansen <john.johansen@canonical.com>
> Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> ---
>  include/linux/cred.h     |  3 ++-
>  include/linux/security.h |  5 +++--
>  kernel/cred.c            | 10 ++++++----
>  security/security.c      | 14 ++++++++++++--
>  4 files changed, 23 insertions(+), 9 deletions(-)

...

> diff --git a/include/linux/security.h b/include/linux/security.h
> index 9d83c6832bae..1bfaf9ece13e 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -439,7 +439,7 @@ void security_cred_free(struct cred *cred);
>  int security_prepare_creds(struct cred *new, const struct cred *old, gfp_t gfp);
>  void security_transfer_creds(struct cred *new, const struct cred *old);
>  void security_cred_getsecid(const struct cred *c, u32 *secid);
> -int security_kernel_act_as(struct cred *new, u32 secid);
> +int security_kernel_act_as(struct cred *new, struct lsmblob *blob);
>  int security_kernel_create_files_as(struct cred *new, struct inode *inode);
>  int security_kernel_module_request(char *kmod_name);
>  int security_kernel_load_data(enum kernel_load_data_id id);
> @@ -1045,7 +1045,8 @@ static inline void security_transfer_creds(struct cred *new,
>  {
>  }
>
> -static inline int security_kernel_act_as(struct cred *cred, u32 secid)
> +static inline int security_kernel_act_as(struct cred *cred,
> +                                        struct lsmblob *blob)
>  {
>         return 0;
>  }
> diff --git a/kernel/cred.c b/kernel/cred.c
> index 809a985b1793..fae63c0a1b36 100644
> --- a/kernel/cred.c
> +++ b/kernel/cred.c
> @@ -732,14 +732,14 @@ EXPORT_SYMBOL(prepare_kernel_cred);
>  /**
>   * set_security_override - Set the security ID in a set of credentials
>   * @new: The credentials to alter
> - * @secid: The LSM security ID to set
> + * @blob: The LSM security information to set
>   *
>   * Set the LSM security ID in a set of credentials so that the subjective
>   * security is overridden when an alternative set of credentials is used.
>   */
> -int set_security_override(struct cred *new, u32 secid)
> +int set_security_override(struct cred *new, struct lsmblob *blob)
>  {
> -       return security_kernel_act_as(new, secid);
> +       return security_kernel_act_as(new, blob);
>  }
>  EXPORT_SYMBOL(set_security_override);
>
> @@ -755,6 +755,7 @@ EXPORT_SYMBOL(set_security_override);
>   */
>  int set_security_override_from_ctx(struct cred *new, const char *secctx)
>  {
> +       struct lsmblob blob;
>         u32 secid;
>         int ret;
>
> @@ -762,7 +763,8 @@ int set_security_override_from_ctx(struct cred *new, const char *secctx)
>         if (ret < 0)
>                 return ret;
>
> -       return set_security_override(new, secid);
> +       lsmblob_init(&blob, secid);
> +       return set_security_override(new, &blob);

See my comments in 03/23, this is another case where the value of
lsmblob is not yet clear to me, but perhaps it will make sense later
in the patchset.

>  }
>  EXPORT_SYMBOL(set_security_override_from_ctx);

-- 
paul moore
www.paul-moore.com