linux-kernel - Re: SHMEM question

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Message-ID: <20091027132548.GD5585@boogie.lpds.sztaki.hu>
Date:	Tue, 27 Oct 2009 14:25:49 +0100
From:	Gabor Gombas <gombasg@...aki.hu>
To:	Gene Heskett <gene.heskett@...izon.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: SHMEM question

On Mon, Oct 26, 2009 at 11:59:04AM -0400, Gene Heskett wrote:

> On looking at it:
> [root@...ote Download]# ls -l /dev/shm
> total 28
> -rw-r----- 1 root root     4096 2009-10-25 12:09 mono.10594
> -r-------- 1 root root 67108904 2009-10-24 00:28 pulse-shm-3880918577
> -rw-rw-rw- 1 root root       16 2009-10-24 01:17 sem.ADBE_ReadPrefs_root
> -rw-rw-rw- 1 root root       16 2009-10-24 01:17 sem.ADBE_REL_root
> -rw-rw-rw- 1 root root       16 2009-10-24 01:17 sem.ADBE_WritePrefs_root
> 
> On grepping for SHM in the .config, I find SHMEM set to y, but about an hours 
> worth of wandering around in a 'make xconfig' has failed to actually find it.

No wonder, it has nothing to do with the kernel. glibc uses /dev/shm to
implement POSIX shared memory, see shm_overview(7).

> That pulse-shm-3880918577 file at over 67 megabytes is all $00 till $04000000 
> into it, then there is 6 non-zero bytes and the rest is back to all balls.

If it bothers you then do not use pulseaudio.

> Is this some indicator of a new rootkit or WTF?

Not neccessarily. However since most people never look into /dev/shm,
it's not a bad place to hide data. But it will go away at reboot, so
it's not that useful for a rootkit.

Gabor

-- 
     ---------------------------------------------------------
     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
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