[PATCH V4 06/10] capabilities: move audit log decision to function

[Kees Cook]

On Mon, Sep 4, 2017 at 11:46 PM, Richard Guy Briggs <rgb at redhat.com> wrote:
> Move the audit log decision logic to its own function to isolate the
> complexity in one place.
>
> Suggested-by: Serge Hallyn <serge at hallyn.com>
> Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
> Reviewed-by: Serge Hallyn <serge at hallyn.com>
> Acked-by: James Morris <james.l.morris at oracle.com>

Acked-by: Kees Cook <keescook at chromium.org>

-Kees

> ---
>  security/commoncap.c |   50 ++++++++++++++++++++++++++++++--------------------
>  1 files changed, 30 insertions(+), 20 deletions(-)
>
> diff --git a/security/commoncap.c b/security/commoncap.c
> index d37ebec..eae7431 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -527,6 +527,32 @@ static inline bool __is_setuid(struct cred *new, const struct cred *old)
>  static inline bool __is_setgid(struct cred *new, const struct cred *old)
>  { return !gid_eq(new->egid, old->gid); }
>
> +/*
> + * Audit candidate if current->cap_effective is set
> + *
> + * We do not bother to audit if 3 things are true:
> + *   1) cap_effective has all caps
> + *   2) we are root
> + *   3) root is supposed to have all caps (SECURE_NOROOT)
> + * Since this is just a normal root execing a process.
> + *
> + * Number 1 above might fail if you don't have a full bset, but I think
> + * that is interesting information to audit.
> + */
> +static inline bool nonroot_raised_pE(struct cred *cred, kuid_t root)
> +{
> +       bool ret = false;
> +
> +       if (__cap_grew(effective, ambient, cred)) {
> +               if (!__cap_full(effective, cred) ||
> +                   !__is_eff(root, cred) || !__is_real(root, cred) ||
> +                   !root_privileged()) {
> +                       ret = true;
> +               }
> +       }
> +       return ret;
> +}
> +
>  /**
>   * cap_bprm_set_creds - Set up the proposed credentials for execve().
>   * @bprm: The execution parameters, including the proposed creds
> @@ -604,26 +630,10 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
>         if (WARN_ON(!cap_ambient_invariant_ok(new)))
>                 return -EPERM;
>
> -       /*
> -        * Audit candidate if current->cap_effective is set
> -        *
> -        * We do not bother to audit if 3 things are true:
> -        *   1) cap_effective has all caps
> -        *   2) we are root
> -        *   3) root is supposed to have all caps (SECURE_NOROOT)
> -        * Since this is just a normal root execing a process.
> -        *
> -        * Number 1 above might fail if you don't have a full bset, but I think
> -        * that is interesting information to audit.
> -        */
> -       if (__cap_grew(effective, ambient, new)) {
> -               if (!__cap_full(effective, new) ||
> -                   !__is_eff(root_uid, new) || !__is_real(root_uid, new) ||
> -                   !root_privileged()) {
> -                       ret = audit_log_bprm_fcaps(bprm, new, old);
> -                       if (ret < 0)
> -                               return ret;
> -               }
> +       if (nonroot_raised_pE(new, root_uid)) {
> +               ret = audit_log_bprm_fcaps(bprm, new, old);
> +               if (ret < 0)
> +                       return ret;
>         }
>
>         new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
> --
> 1.7.1
>



-- 
Kees Cook
Pixel Security
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