From: Pekka Enberg <penberg@kernel.org>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
lizf@cn.fujitsu.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, Tyler Hicks <tyhicks@canonical.com>,
Dustin Kirkland <kirkland@canonical.com>,
ecryptfs@vger.kernel.org
Subject: Re: [PATCH] mm: Don't warn if memdup_user fails
Date: Thu, 12 Jan 2012 10:15:50 +0200 [thread overview]
Message-ID: <CAOJsxLEYY=ZO8QrxiWL6qAxPzsPpZj3RsF9cXY0Q2L44+sn7JQ@mail.gmail.com> (raw)
In-Reply-To: <1326355594.1999.7.camel@lappy>
On Thu, Jan 12, 2012 at 10:06 AM, Sasha Levin <levinsasha928@gmail.com> wrote:
> Let's split it to two parts: the specific ecryptfs issue I've given as
> an example here, and a general view about memdup_user().
>
> I fully agree that in the case of ecryptfs there's a missing validity
> check, and just calling memdup_user() with whatever the user has passed
> to it is wrong and dangerous. This should be fixed in the ecryptfs code
> and I'll send a patch to do that.
>
> The other part, is memdup_user() itself. Kernel warnings are usually
> reserved (AFAIK) to cases where it would be difficult to notify the user
> since it happens in a flow which the user isn't directly responsible
> for.
>
> memdup_user() is always located in path which the user has triggered,
> and is usually almost the first thing we try doing in response to the
> trigger. In those code flows it doesn't make sense to print a kernel
> warnings and taint the kernel, instead we can simply notify the user
> about that error and let him deal with it any way he wants.
>
> There are more reasons kalloc() can show warnings besides just trying to
> allocate too much, and theres no reason to dump kernel warnings when
> it's easier to notify the user.
I think you missed Andrew's point. We absolutely want to issue a
kernel warning here because ecryptfs is misusing the memdup_user()
API. We must not let userspace processes allocate large amounts of
memory arbitrarily.
Pekka
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2012-01-12 8:15 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-11 16:50 Sasha Levin
2012-01-11 21:46 ` David Rientjes
2012-01-12 6:43 ` Pekka Enberg
2012-01-12 6:44 ` Pekka Enberg
2012-01-12 9:09 ` Li Zefan
2012-01-11 22:12 ` Andrew Morton
2012-01-12 7:12 ` Pekka Enberg
2012-01-12 8:06 ` Sasha Levin
2012-01-12 8:15 ` Pekka Enberg [this message]
2012-01-12 21:19 ` David Rientjes
2012-01-12 21:58 ` Andrew Morton
2012-01-12 22:29 ` David Rientjes
2012-01-13 7:17 ` Dan Carpenter
2012-01-13 7:36 ` Andrew Morton
2012-01-12 11:16 ` Tyler Hicks
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAOJsxLEYY=ZO8QrxiWL6qAxPzsPpZj3RsF9cXY0Q2L44+sn7JQ@mail.gmail.com' \
--to=penberg@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=ecryptfs@vger.kernel.org \
--cc=kirkland@canonical.com \
--cc=levinsasha928@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=lizf@cn.fujitsu.com \
--cc=tyhicks@canonical.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox