From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762288AbXKOGOm (ORCPT ); Thu, 15 Nov 2007 01:14:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758713AbXKOGK7 (ORCPT ); Thu, 15 Nov 2007 01:10:59 -0500 Received: from pentafluge.infradead.org ([213.146.154.40]:36568 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758670AbXKOGK5 (ORCPT ); Thu, 15 Nov 2007 01:10:57 -0500 Date: Wed, 14 Nov 2007 22:09:55 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org, torvalds@linux-foundation.org Cc: Justin Forbes , Zwane Mwaikambo , "Theodore Ts'o" , Randy Dunlap , Dave Jones , Chuck Wolber , Chris Wedgwood , Michael Krufky , Chuck Ebbert , Domenico Andreoli , akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, penberg@cs.helsinki.fi, hugh@veritas.com, ezk@cs.sunysb.edu Subject: [patch 12/13] fix tmpfs BUG and AOP_WRITEPAGE_ACTIVATE Message-ID: <20071115060955.GM7602@kroah.com> References: <20071115042610.731859958@mini.kroah.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline; filename="fix-tmpfs-bug-and-aop_writepage_activate.patch" In-Reply-To: <20071115060544.GA7602@kroah.com> User-Agent: Mutt/1.5.16 (2007-06-09) X-Bad-Reply: References and In-Reply-To but no 'Re:' in Subject. Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org -stable review patch. If anyone has any objections, please let us know. ------------------ From: Hugh Dickins patch 487e9bf25cbae11b131d6a14bdbb3a6a77380837 in mainline. It's possible to provoke unionfs (not yet in mainline, though in mm and some distros) to hit shmem_writepage's BUG_ON(page_mapped(page)). I expect it's possible to provoke the 2.6.23 ecryptfs in the same way (but the 2.6.24 ecryptfs no longer calls lower level's ->writepage). This came to light with the recent find that AOP_WRITEPAGE_ACTIVATE could leak from tmpfs via write_cache_pages and unionfs to userspace. There's already a fix (e423003028183df54f039dfda8b58c49e78c89d7 - writeback: don't propagate AOP_WRITEPAGE_ACTIVATE) in the tree for that, and it's okay so far as it goes; but insufficient because it doesn't address the underlying issue, that shmem_writepage expects to be called only by vmscan (relying on backing_dev_info capabilities to prevent the normal writeback path from ever approaching it). That's an increasingly fragile assumption, and ramdisk_writepage (the other source of AOP_WRITEPAGE_ACTIVATEs) is already careful to check wbc->for_reclaim before returning it. Make the same check in shmem_writepage, thereby sidestepping the page_mapped BUG also. Signed-off-by: Hugh Dickins Cc: Erez Zadok Reviewed-by: Pekka Enberg Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/shmem.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) --- a/mm/shmem.c +++ b/mm/shmem.c @@ -916,6 +916,21 @@ static int shmem_writepage(struct page * struct inode *inode; BUG_ON(!PageLocked(page)); + /* + * shmem_backing_dev_info's capabilities prevent regular writeback or + * sync from ever calling shmem_writepage; but a stacking filesystem + * may use the ->writepage of its underlying filesystem, in which case + * we want to do nothing when that underlying filesystem is tmpfs + * (writing out to swap is useful as a response to memory pressure, but + * of no use to stabilize the data) - just redirty the page, unlock it + * and claim success in this case. AOP_WRITEPAGE_ACTIVATE, and the + * page_mapped check below, must be avoided unless we're in reclaim. + */ + if (!wbc->for_reclaim) { + set_page_dirty(page); + unlock_page(page); + return 0; + } BUG_ON(page_mapped(page)); mapping = page->mapping; --