Help: World Writable Files under /dev directory

Kanwal Kalra

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Aug 19, 1996, 3:00:00 AM8/19/96

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Hello,

I would appreciate if someone could help me to answer the following
questions related to the file access on the NCR SVR4 platform:

(1) Why should other have access in /dev/fd/ directory. The type of
files in this directory are "c", and are like: /dev/fd/256, /dev/fd/257
.. and so on?

(2) Why is /etc/batch.d/msgfile world-writable and why is it there? I
removed the world writable permissions, but when rebooted the system,
the file got its original permissions.

(3) (same as 1) why are the files under: /dev/dsk, /dev/nty, /dev/pty
world-writable?

Can I remove the world-writable permissions?

I Will appreciate your feedback.

Thanks.

Kanwal.

Chuck Adams

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Aug 20, 1996, 3:00:00 AM8/20/96

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In article <3218B9...@passport.ca>, Kanwal Kalra <kka...@passport.ca> wrote:
>(3) (same as 1) why are the files under: /dev/dsk, /dev/nty, /dev/pty
>world-writable?
>
>Can I remove the world-writable permissions?
>

Not if you want anyone to be able to write to their directories or type on
their terminals :) Relax, they can't delete the files. Actually, I think the
most common boneheaded move some folks make is to remove world-writability
from /dev/null

For some odd reason, I have seen /dev/zero not world-writable. Anyone fancy a
reason why?

Brendan O'Dea

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Aug 21, 1996, 3:00:00 AM8/21/96

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In article <4vcj6u$k...@butch.lmsc.lockheed.com>,
Chuck Adams <cad...@msgate.litc.lockheed.com> wrote:
[snip]

>their terminals :) Relax, they can't delete the files. Actually, I think the
>most common boneheaded move some folks make is to remove world-writability
>from /dev/null
>
>For some odd reason, I have seen /dev/zero not world-writable. Anyone fancy a
>reason why?

Hmmm,

$ apropos zero
zero (7) - source of zeroes
^^^^^^
I think this might be the key <g>. Since /dev/null and /dev/zero are
equivalent for _writes_, some vendors may have decided that /dev/zero
need not be writable.

Regards,
--
Brendan O'Dea b...@tyndall.com.au
Compusol Pty. Limited (NSW, Australia) +61 2 9809 0133

Mark Sitkowski

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Aug 22, 1996, 3:00:00 AM8/22/96

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Brendan O'Dea wrote:
>
> In article <4vcj6u$k...@butch.lmsc.lockheed.com>,
> Chuck Adams <cad...@msgate.litc.lockheed.com> wrote:
> [snip]
> >their terminals :) Relax, they can't delete the files. Actually, I think the
> >most common boneheaded move some folks make is to remove world-writability
> >from /dev/null
> >
> >For some odd reason, I have seen /dev/zero not world-writable. Anyone fancy a
> >reason why?
>
> Hmmm,
>
> $ apropos zero
> zero (7) - source of zeroes
> ^^^^^^
> I think this might be the key <g>. Since /dev/null and /dev/zero are
> equivalent for _writes_, some vendors may have decided that /dev/zero
> need not be writable.
>

It really worries me when someone finds something he doesn't understand
and either deletes it or tweaks it.

I think I'd be very worried if a sys admin asked why there was a 'c'
in the listing of /dev files, and why they were world writeable.
a bit like this, perhaps?
crw-rw-rw- 1 root system 14, 0 Aug 09 12:45 /dev/rfd0

Come on, RTFM, before you break something.

I almost wish he had deleted /dev/zero since it had no apparent
function. The system would have been impossible to boot, without a
lot of hard work, since /dev/zero supplies zeros for memory testing
at boot time.

--
Best regards,
Mark

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