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Message-ID: <874mnyxtk2.fsf@rustcorp.com.au>
Date: Thu, 30 Apr 2015 11:32:05 +0930
From: Rusty Russell <rusty@...tcorp.com.au>
To: Gobinda Maji <gobinda.cemk07@...il.com>
Cc: linux-next@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] sysfs: disallow world-writable files.
Gobinda Maji <gobinda.cemk07@...il.com> 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.
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