linux-kernel - Re: [PATCH 3/3] uprobes: write_opcode()->__replace_page() can race with try_to

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]

Date:	Fri, 08 Jun 2012 10:47:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] uprobes: write_opcode()->__replace_page() can race
 with try_to_unmap()

On Thu, 2012-06-07 at 19:00 +0200, Oleg Nesterov wrote:
> write_opcode() gets old_page via get_user_pages() and then calls
> __replace_page() which assumes that this old_page is still mapped
> after pte_offset_map_lock().
> 
> This is not true if this old_page was already try_to_unmap()'ed,
> and in this case everything __replace_page() does with old_page
> is wrong. Just for example, put_page() is not balanced.
> 
> I think it is possible to teach __replace_page() to handle this
> unlikely case correctly, but this patch simply changes it to use
> page_check_address() and return -EAGAIN if it fails. The caller
> should notice this error code and retry. 

Note that replace_page() was nicked from ksm, does that suffer a similar
problem?
--
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/