LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Jonathan Corbet <corbet@lwn.net>
Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
	torvalds@linux-foundation.org
Subject: Re: [PATCH] Avoid buffer overflows in get_user_pages()
Date: Tue, 12 Feb 2008 10:45:14 +1100	[thread overview]
Message-ID: <200802121045.15095.nickpiggin@yahoo.com.au> (raw)
In-Reply-To: <5758.1202771853@vena.lwn.net>

On Tuesday 12 February 2008 10:17, Jonathan Corbet wrote:
> Avoid buffer overflows in get_user_pages()
>
> So I spent a while pounding my head against my monitor trying to figure
> out the vmsplice() vulnerability - how could a failure to check for
> *read* access turn into a root exploit?  It turns out that it's a buffer
> overflow problem which is made easy by the way get_user_pages() is
> coded.
>
> In particular, "len" is a signed int, and it is only checked at the
> *end* of a do {} while() loop.  So, if it is passed in as zero, the loop
> will execute once and decrement len to -1.  At that point, the loop will
> proceed until the next invalid address is found; in the process, it will
> likely overflow the pages array passed in to get_user_pages().
>
> I think that, if get_user_pages() has been asked to grab zero pages,
> that's what it should do.  Thus this patch; it is, among other things,
> enough to block the (already fixed) root exploit and any others which
> might be lurking in similar code.  I also think that the number of pages
> should be unsigned, but changing the prototype of this function probably
> requires some more careful review.
>
> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
>
> diff --git a/mm/memory.c b/mm/memory.c
> index e5628a5..7f50fd8 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -989,6 +989,8 @@ int get_user_pages(struct task_struct *tsk, struct
> mm_struct *mm, int i;
>  	unsigned int vm_flags;
>
> +	if (len <= 0)
> +		return 0;

BUG_ON()?

  reply	other threads:[~2008-02-12  1:49 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-11 23:17 Jonathan Corbet
2008-02-11 23:45 ` Nick Piggin [this message]
2008-02-12  7:46 ` Andrew Morton
2008-02-12 10:35   ` Jiri Kosina
2008-02-14 16:45 ` Oliver Pinter
2008-02-14 21:09   ` Jonathan Corbet
     [not found] <fa.5jOFf0zR7ZoK3hLDItf3Omow4lE@ifi.uio.no>
     [not found] ` <fa.NNs+hqAlLlf93+yNZ/YJzSyGQbs@ifi.uio.no>
2008-02-12  3:16   ` Robert Hancock
2008-02-12  5:56     ` Nick Piggin
     [not found] <9VQ6w-5Xn-7@gated-at.bofh.it>
     [not found] ` <9VY4a-1tI-21@gated-at.bofh.it>
2008-02-12  8:34   ` Bodo Eggert

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=200802121045.15095.nickpiggin@yahoo.com.au \
    --to=nickpiggin@yahoo.com.au \
    --cc=akpm@linux-foundation.org \
    --cc=corbet@lwn.net \
    --cc=linux-kernel@vger.kernel.org \
    --cc=torvalds@linux-foundation.org \
    --subject='Re: [PATCH] Avoid buffer overflows in get_user_pages()' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).