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Subject: Re: [PATCH] ksys_mount: check for permissions before resource
 allocation
From: Ilya Matveychikov <matvejchikov@gmail.com>
In-Reply-To: <20180605112641.GN30522@ZenIV.linux.org.uk>
Date: Tue, 5 Jun 2018 15:35:55 +0400
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Message-Id: <1E519BA2-4198-4255-BAE4-3125C59741A3@gmail.com>
References: <D2317950-0DB0-4311-ADB1-FF677B676E04@gmail.com>
 <BD48252B-65D7-4238-BDA2-71BAC1CEA855@gmail.com>
 <20180605112641.GN30522@ZenIV.linux.org.uk>
To: Al Viro <viro@ZenIV.linux.org.uk>
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> On Jun 5, 2018, at 3:26 PM, Al Viro <viro@ZenIV.linux.org.uk> wrote:
>> 
>>> On Jun 5, 2018, at 6:00 AM, Ilya Matveychikov <matvejchikov@gmail.com> wrote:
>>> 
>>> Early check for mount permissions prevents possible allocation of 3
>>> pages from kmalloc() pool by unpriveledged user which can be used for
>>> spraying the kernel heap.
> 
> I'm sorry, but there are arseloads of unpriveleged syscalls that do the same,
> starting with read() from procfs files.  So what the hell does it buy?

Means that if all do the same shit no reason to fix it? Sounds weird...