linux-kernel - Re: [PATCH] Avoid buffer overflows in get_user

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <200802121045.15095.nickpiggin@yahoo.com.au>
Date:	Tue, 12 Feb 2008 10:45:14 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Jonathan Corbet <corbet@....net>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH] Avoid buffer overflows in get_user_pages()

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@....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()?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/