[PATCH V3 01/10] capabilities: factor out cap_bprm_set_creds privileged root

[Serge E. Hallyn]

Quoting Richard Guy Briggs (rgb at redhat.com):
> Factor out the case of privileged root from the function
> cap_bprm_set_creds() to make the latter easier to read and analyse.
> 
> Suggested-by: Serge Hallyn <serge at hallyn.com>

Reviewed-by: Serge Hallyn <serge at hallyn.com>

> Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
> ---
>  security/commoncap.c |   62 +++++++++++++++++++++++++++----------------------
>  1 files changed, 34 insertions(+), 28 deletions(-)
> 
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 78b3783..b7fbf77 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -481,6 +481,38 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
>  	return rc;
>  }
>  
> +void handle_privileged_root(struct linux_binprm *bprm, bool has_cap, bool *effective, kuid_t root_uid)
> +{
> +	const struct cred *old = current_cred();
> +	struct cred *new = bprm->cred;
> +
> +	if (issecure(SECURE_NOROOT))
> +		return;
> +	/*
> +	 * If the legacy file capability is set, then don't set privs
> +	 * for a setuid root binary run by a non-root user.  Do set it
> +	 * for a root user just to cause least surprise to an admin.
> +	 */
> +	if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
> +		warn_setuid_and_fcaps_mixed(bprm->filename);
> +		return;
> +	}
> +	/*
> +	 * To support inheritance of root-permissions and suid-root
> +	 * executables under compatibility mode, we override the
> +	 * capability sets for the file.
> +	 *
> +	 * If only the real uid is 0, we do not set the effective bit.
> +	 */
> +	if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
> +		/* pP' = (cap_bset & ~0) | (pI & ~0) */
> +		new->cap_permitted = cap_combine(old->cap_bset,
> +						 old->cap_inheritable);
> +	}
> +	if (uid_eq(new->euid, root_uid))
> +		*effective = true;
> +}
> +
>  /**
>   * cap_bprm_set_creds - Set up the proposed credentials for execve().
>   * @bprm: The execution parameters, including the proposed creds
> @@ -493,46 +525,20 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
>  {
>  	const struct cred *old = current_cred();
>  	struct cred *new = bprm->cred;
> -	bool effective, has_cap = false, is_setid;
> +	bool effective = false, has_cap = false, is_setid;
>  	int ret;
>  	kuid_t root_uid;
>  
>  	if (WARN_ON(!cap_ambient_invariant_ok(old)))
>  		return -EPERM;
>  
> -	effective = false;
>  	ret = get_file_caps(bprm, &effective, &has_cap);
>  	if (ret < 0)
>  		return ret;
>  
>  	root_uid = make_kuid(new->user_ns, 0);
>  
> -	if (!issecure(SECURE_NOROOT)) {
> -		/*
> -		 * If the legacy file capability is set, then don't set privs
> -		 * for a setuid root binary run by a non-root user.  Do set it
> -		 * for a root user just to cause least surprise to an admin.
> -		 */
> -		if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
> -			warn_setuid_and_fcaps_mixed(bprm->filename);
> -			goto skip;
> -		}
> -		/*
> -		 * To support inheritance of root-permissions and suid-root
> -		 * executables under compatibility mode, we override the
> -		 * capability sets for the file.
> -		 *
> -		 * If only the real uid is 0, we do not set the effective bit.
> -		 */
> -		if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
> -			/* pP' = (cap_bset & ~0) | (pI & ~0) */
> -			new->cap_permitted = cap_combine(old->cap_bset,
> -							 old->cap_inheritable);
> -		}
> -		if (uid_eq(new->euid, root_uid))
> -			effective = true;
> -	}
> -skip:
> +	handle_privileged_root(bprm, has_cap, &effective, root_uid);
>  
>  	/* if we have fs caps, clear dangerous personality flags */
>  	if (!cap_issubset(new->cap_permitted, old->cap_permitted))
> -- 
> 1.7.1
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