capabilities: factor out cap_bprm_set_creds privileged root

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@hallyn.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Acked-by: James Morris <james.l.morris@oracle.com>
Acked-by: Kees Cook <keescook@chromium.org>
Okay-ished-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

diff --git a/security/commoncap.c b/security/commoncap.c
index c25e0d27537f87ea7d7d216b9448f47b83e26608..be9bca50c3120bad7351bbcd5f056252b2b2a50c 100644 (file)
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -695,6 +695,52 @@ out:
        return rc;
 }
 
+/*
+ * handle_privileged_root - Handle case of privileged root
+ * @bprm: The execution parameters, including the proposed creds
+ * @has_fcap: Are any file capabilities set?
+ * @effective: Do we have effective root privilege?
+ * @root_uid: This namespace' root UID WRT initial USER namespace
+ *
+ * Handle the case where root is privileged and hasn't been neutered by
+ * SECURE_NOROOT.  If file capabilities are set, they won't be combined with
+ * set UID root and nothing is changed.  If we are root, cap_permitted is
+ * updated.  If we have become set UID root, the effective bit is set.
+ */
+static 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 (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 only the real uid is 0, we do not set the effective bit.
+        */
+       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
@@ -707,46 +753,20 @@ 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))