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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Michal Hocko <mhocko@suse.com>
Cc: Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Lee Duncan <lduncan@suse.com>, Chris Leech <cleech@redhat.com>,
	Adam Nichols <adam@grimm-co.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-hardening@vger.kernel.org,
	Uladzislau Rezki <urezki@gmail.com>
Subject: Re: [PATCH v2] seq_file: Unconditionally use vmalloc for buffer
Date: Wed, 17 Mar 2021 14:34:27 +0100	[thread overview]
Message-ID: <YFIFY7mj65sStba1@kroah.com> (raw)
In-Reply-To: <YFHxNT1Pwoslmhxq@dhcp22.suse.cz>

On Wed, Mar 17, 2021 at 01:08:21PM +0100, Michal Hocko wrote:
> Btw. I still have problems with the approach. seq_file is intended to
> provide safe way to dump values to the userspace. Sacrificing
> performance just because of some abuser seems like a wrong way to go as
> Al pointed out earlier. Can we simply stop the abuse and disallow to
> manipulate the buffer directly? I do realize this might be more tricky
> for reasons mentioned in other emails but this is definitely worth
> doing.

We have to provide a buffer to "write into" somehow, so what is the best
way to stop "abuse" like this?

Right now, we do have helper functions, sysfs_emit(), that know to stop
the overflow of the buffer size, but porting the whole kernel to them is
going to take a bunch of churn, for almost no real benefit except a
potential random driver that might be doing bad things here that we have
not noticed yet.

Other than that, suggestions are welcome!

thanks,

greg k-h

  reply	other threads:[~2021-03-17 13:35 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-15 17:48 Kees Cook
2021-03-15 18:33 ` Al Viro
2021-03-15 20:43   ` Kees Cook
2021-03-16  7:24     ` Greg Kroah-Hartman
2021-03-16 12:43       ` Al Viro
2021-03-16 12:55         ` Greg Kroah-Hartman
2021-03-16 13:01         ` Michal Hocko
2021-03-16 19:18         ` Kees Cook
2021-03-17 10:44           ` Greg Kroah-Hartman
2021-03-16  8:31 ` Michal Hocko
2021-03-16 19:08   ` Kees Cook
2021-03-17 12:08     ` Michal Hocko
2021-03-17 13:34       ` Greg Kroah-Hartman [this message]
2021-03-17 14:44         ` Michal Hocko
2021-03-17 14:56           ` Greg Kroah-Hartman
2021-03-17 15:20             ` Michal Hocko
2021-03-17 15:38               ` Greg Kroah-Hartman
2021-03-17 15:48                 ` Michal Hocko
2021-03-17 21:30                 ` Kees Cook
2021-03-18  8:07                   ` Greg Kroah-Hartman
2021-03-18 15:51                     ` Kees Cook
2021-03-18 17:56                       ` Greg Kroah-Hartman
2021-03-19 14:07 ` [seq_file] 5fd6060e50: stress-ng.eventfd.ops_per_sec -49.1% regression kernel test robot
2021-03-19 19:31   ` Kees Cook

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