linux-kernel - adjust /proc/PID/oom_score_adj with CAP_SYS

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Message-ID: <CAG5DWojOsLa_SXaLR8_z4FVchqzwQM4vCNC_MUg27Z918ExPzw@mail.gmail.com>
Date:	Sun, 20 Oct 2013 00:33:07 +0400
From:	Azat Khuzhin <a.khuzhin@...rush.com>
To:	open list <linux-kernel@...r.kernel.org>
Subject: adjust /proc/PID/oom_score_adj with CAP_SYS_RESOURCE

Recently I needed in adjusting /proc/PID/oom_score_adj to disable oom killer,
but I didn't want to add suid/or run from root that binary.

I decided to use CAP_SYS_RESOURCE. However it didn't work.

I gdb/strace/printk a lot, and finally found the reason,
the process can't open this file for writing because pid_revalidate()
change i_uid/i_gid for it to GLOBAL_ROOT_UID/GID.
And to bypass this check I must to use CAP_DAC_OVERRIDE, which is not so good,
because this will allow more capabilities than I need for that binary.

Is this works by design,
and/or is there another way to do this without suid/root?

Thanks!

-- 
Respectfully
Azat Khuzhin
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