From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH 9/9] sysfs: disallow world-writable files. Date: Thu, 30 Apr 2015 11:32:05 +0930 Message-ID: <874mnyxtk2.fsf@rustcorp.com.au> References: Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Gobinda Maji Cc: linux-next@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-next.vger.kernel.org Gobinda Maji writes: > Hi Rusty, Hi Gobinda, > I have a small doubt about the permission restriction (User perms >= > group perms >= other perms) in VERIFY_OCTAL_PERMISSIONS(). Please Note > that permission field of User, Group or Other consists of three bits. > LSB is EXECUTE permission, MSB is READ permission and the middle bit > is WRITE permission. Say for example, permission value is "0431". Here > User has only READ permission whereas Group has both WRITE and EXECUTE > permission and Other has EXECUTE permission. I guess, it is not good > to give Group the WRITE permission whereas User itself has no WRITE > permission. You're absolutely right, well spotted! The checks can be tightened. We don't really care about execute, but logically write is "more privileged" than read. Best to separate the tests; OTHER_WRITABLE <= GROUP_WRITABLE <= OWNER_WRITABLE and OTHER_READABLE <= GROUP_READABLE <= OWNER_READABLE. A patch would be welcome! Thanks, Rusty.