linux-kernel - Re: [PATCH] kmsg: Use vmalloc instead of kmalloc when writing

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Message-ID: <CA+1xoqdZnxcWNpL-03xsR+RDcz3=aRbx2LbR6mTJ_gCmwp-0Rw@mail.gmail.com>
Date:	Fri, 30 Mar 2012 19:37:37 +0300
From:	Sasha Levin <levinsasha928@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	arnd@...db.de, viro@...iv.linux.org.uk, davej@...hat.com,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kmsg: Use vmalloc instead of kmalloc when writing

On Fri, Mar 30, 2012 at 6:30 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Fri, Mar 30, 2012 at 01:04:27PM -0400, Sasha Levin wrote:
>> There are no size checks in kmsg_write(), and we try allocating enough
>> memory to store everything userspace gave us, which may be too much for
>> kmalloc to allocate.
>
> Really?  Have you seen this fail?  As only root can do this, is this
> really a problem?

Only root, and a whole bunch of management software that dumps data
into /dev/kmsg (systemd and friends).

>> One option would be to limit it to something, but we can't come up with
>> a number that would make sense.
>>
>> Instead, just use vmalloc so that nothing would break with large amounts
>> of data.
>
> Are you sure this will work properly?  Have you tested it with large
> amounts of data?

My test was dumping 800mb of data into it, if there's anything else I
should try please let me know.

Thanks.
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