linux-kernel - Re: [PATCH] ksys_mount: check for permissions before resource allocation

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Message-ID: <20180605112641.GN30522@ZenIV.linux.org.uk>
Date:   Tue, 5 Jun 2018 12:26:41 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Ilya Matveychikov <matvejchikov@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] ksys_mount: check for permissions before resource
 allocation

On Tue, Jun 05, 2018 at 10:59:51AM +0400, Ilya Matveychikov wrote:
> Just CC’ed to some of maintainers.
> 
> $ perl scripts/get_maintainer.pl fs/0001-ksys_mount-check-for-permissions-before-resource-all.patch
> Alexander Viro <viro@...iv.linux.org.uk> (maintainer:FILESYSTEMS (VFS and infrastructure))
> linux-fsdevel@...r.kernel.org (open list:FILESYSTEMS (VFS and infrastructure))
> linux-kernel@...r.kernel.org (open list)
> 
> > On Jun 5, 2018, at 6:00 AM, Ilya Matveychikov <matvejchikov@...il.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?