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

[Al Viro]

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