[PATCH V4 10/10] capabilities: audit log other surprising conditions

[Kees Cook]

On Mon, Sep 4, 2017 at 11:46 PM, Richard Guy Briggs <rgb at redhat.com> wrote:
> The existing condition tested for process effective capabilities set by
> file attributes but intended to ignore the change if the result was
> unsurprisingly an effective full set in the case root is special with a
> setuid root executable file and we are root.
>
> Stated again:
> - When you execute a setuid root application, it is no surprise and
>   expected that it got all capabilities, so we do not want capabilities
>   recorded.
>         if (pE_grew && !(pE_fullset && (eff_root || real_root) && root_priveleged) )
>
> Now make sure we cover other cases:
> - If something prevented a setuid root app getting all capabilities and
>   it wound up with one capability only, then it is a surprise and should
>   be logged.  When it is a setuid root file, we only want capabilities
>   when the process does not get full capabilities..
>         root_priveleged && setuid_root && !pE_fullset
>
> - Similarly if a non-setuid program does pick up capabilities due to
>   file system based capabilities, then we want to know what capabilities
>   were picked up.  When it has file system based capabilities we want
>   the capabilities.
>         !is_setuid && (has_fcap && pP_gained)
>
> - If it is a non-setuid file and it gets ambient capabilities, we want
>   the capabilities.
>         !is_setuid && pA_gained
>
> - These last two are combined into one due to the common first parameter.
>
> Related: https://github.com/linux-audit/audit-kernel/issues/16
>
> 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>

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

-Kees

> ---
>  security/commoncap.c |   29 ++++++++++++++++++++++-------
>  1 files changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 759f3fa..afebfd3 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -528,7 +528,7 @@ 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
> + * 1) 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
> @@ -538,16 +538,31 @@ static inline bool __is_setgid(struct cred *new, const struct cred *old)
>   *
>   * Number 1 above might fail if you don't have a full bset, but I think
>   * that is interesting information to audit.
> + *
> + * A number of other conditions require logging:
> + * 2) something prevented setuid root getting all caps
> + * 3) non-setuid root gets fcaps
> + * 4) non-setuid root gets ambient
>   */
> -static inline bool nonroot_raised_pE(struct cred *cred, kuid_t root)
> +static inline bool nonroot_raised_pE(struct cred *new, const struct cred *old,
> +                                    kuid_t root, bool has_fcap)
>  {
>         bool ret = false;
>
> -       if (__cap_grew(effective, ambient, cred) &&
> -           !(__cap_full(effective, cred) &&
> -             (__is_eff(root, cred) || __is_real(root, cred)) &&
> -             root_privileged()))
> +       if ((__cap_grew(effective, ambient, new) &&
> +            !(__cap_full(effective, new) &&
> +              (__is_eff(root, new) || __is_real(root, new)) &&
> +              root_privileged())) ||
> +           (root_privileged() &&
> +            __is_suid(root, new) &&
> +            !__cap_full(effective, new)) ||
> +           (!__is_setuid(new, old) &&
> +            ((has_fcap &&
> +              __cap_gained(permitted, new, old)) ||
> +             __cap_gained(ambient, new, old))))
> +
>                 ret = true;
> +
>         return ret;
>  }
>
> @@ -628,7 +643,7 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
>         if (WARN_ON(!cap_ambient_invariant_ok(new)))
>                 return -EPERM;
>
> -       if (nonroot_raised_pE(new, root_uid)) {
> +       if (nonroot_raised_pE(new, old, root_uid, has_fcap)) {
>                 ret = audit_log_bprm_fcaps(bprm, new, old);
>                 if (ret < 0)
>                         return ret;
> --
> 1.7.1
>



-- 
Kees Cook
Pixel Security
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