selinux: only invoke capabilities and selinux for CAP_MAC_ADMIN checks

SELinux uses CAP_MAC_ADMIN to control the ability to get or set a raw,
uninterpreted security context unknown to the currently loaded security
policy. When performing these checks, we only want to perform a base
capabilities check and a SELinux permission check.  If any other
modules that implement a capable hook are stacked with SELinux, we do
not want to require them to also have to authorize CAP_MAC_ADMIN,
since it may have different implications for their security model.
Rework the CAP_MAC_ADMIN checks within SELinux to only invoke the
capabilities module and the SELinux permission checking.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 735609b..dddb81e 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3107,6 +3107,18 @@ static int selinux_inode_setotherxattr(struct dentry *dentry, const char *name)
        return dentry_has_perm(cred, dentry, FILE__SETATTR);
 }
 
+static bool has_cap_mac_admin(bool audit)
+{
+       const struct cred *cred = current_cred();
+       int cap_audit = audit ? SECURITY_CAP_AUDIT : SECURITY_CAP_NOAUDIT;
+
+       if (cap_capable(cred, &init_user_ns, CAP_MAC_ADMIN, cap_audit))
+               return false;
+       if (cred_has_capability(cred, CAP_MAC_ADMIN, cap_audit, true))
+               return false;
+       return true;
+}
+
 static int selinux_inode_setxattr(struct dentry *dentry, const char *name,
                                  const void *value, size_t size, int flags)
 {
@@ -3138,7 +3150,7 @@ static int selinux_inode_setxattr(struct dentry *dentry, const char *name,
 
        rc = security_context_to_sid(value, size, &newsid, GFP_KERNEL);
        if (rc == -EINVAL) {
-               if (!capable(CAP_MAC_ADMIN)) {
+               if (!has_cap_mac_admin(true)) {
                        struct audit_buffer *ab;
                        size_t audit_size;
                        const char *str;
@@ -3264,13 +3276,8 @@ static int selinux_inode_getsecurity(struct inode *inode, const char *name, void
         * and lack of permission just means that we fall back to the
         * in-core context value, not a denial.
         */
-       error = cap_capable(current_cred(), &init_user_ns, CAP_MAC_ADMIN,
-                           SECURITY_CAP_NOAUDIT);
-       if (!error)
-               error = cred_has_capability(current_cred(), CAP_MAC_ADMIN,
-                                           SECURITY_CAP_NOAUDIT, true);
        isec = inode_security(inode);
-       if (!error)
+       if (has_cap_mac_admin(false))
                error = security_sid_to_context_force(isec->sid, &context,
                                                      &size);
        else
@@ -5919,7 +5926,7 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
                }
                error = security_context_to_sid(value, size, &sid, GFP_KERNEL);
                if (error == -EINVAL && !strcmp(name, "fscreate")) {
-                       if (!capable(CAP_MAC_ADMIN)) {
+                       if (!has_cap_mac_admin(true)) {
                                struct audit_buffer *ab;
                                size_t audit_size;