linux-kernel - Writing CD/DVD on devices opened for read-only. Is it bad?

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Message-ID: <CAEUiM9MB5VRwoG5-Ay6m0Z5RhtfhbO6w4zteaUj5KpautY5HiQ@mail.gmail.com>
Date:	Wed, 19 Oct 2011 14:20:44 +0400
From:	Igor Zhbanov <izh1979@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Writing CD/DVD on devices opened for read-only. Is it bad?

Hello!

I have a question about permissions needed for CD/DVD writing.
As I see in source code user must have capability CAP_SYS_RAWIO for
CD/DVD writing
in 2.6 kernels (I'm not sure that it is needed for all types of disk writing),
but (it seems that) kernel ignores device file permissions. So you can
open /dev/cdrom
for read-only and use IOCTLs for blanking disks and CD/DVD writing.

I think that f_mode for device file should be checked. Isn't it bad to
permit "writable" IOCTLs
for devices opened read-only?

Thanks.
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