From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C3B5C4332F for ; Mon, 14 Nov 2022 12:58:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237609AbiKNM6p (ORCPT ); Mon, 14 Nov 2022 07:58:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52346 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237605AbiKNM6o (ORCPT ); Mon, 14 Nov 2022 07:58:44 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3A06824F11 for ; Mon, 14 Nov 2022 04:58:42 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CE98C6117F for ; Mon, 14 Nov 2022 12:58:41 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BD1D1C433C1; Mon, 14 Nov 2022 12:58:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1668430721; bh=+Tj2vFJtVfp5fkgsnMbug88MZzSZsO3lecwn8EWmk6E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=USm2jygl1Jwu6ymv9E5LizWUcrCmhFD+oizxAQ3kdFXrnuyph2fm/FSYC/wrjEV9q NyV/19wZJ1d5OIVhN7VlAcXLZmbpXtI0tFhMFQ+IT4ysnAi0O0dFrpKPQGvV2Z801l QwVeh7X8osxSHUJRr1T2GdhQebTYhv1ziWXzOEAQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Peter Xu , Matthew Wilcox , Andrea Arcangeli , Hugh Dickins , Axel Rasmussen , Andrew Morton Subject: [PATCH 5.15 111/131] mm/shmem: use page_mapping() to detect page cache for uffd continue Date: Mon, 14 Nov 2022 13:46:20 +0100 Message-Id: <20221114124453.393346098@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221114124448.729235104@linuxfoundation.org> References: <20221114124448.729235104@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Peter Xu commit 93b0d9178743a68723babe8448981f658aebc58e upstream. mfill_atomic_install_pte() checks page->mapping to detect whether one page is used in the page cache. However as pointed out by Matthew, the page can logically be a tail page rather than always the head in the case of uffd minor mode with UFFDIO_CONTINUE. It means we could wrongly install one pte with shmem thp tail page assuming it's an anonymous page. It's not that clear even for anonymous page, since normally anonymous pages also have page->mapping being setup with the anon vma. It's safe here only because the only such caller to mfill_atomic_install_pte() is always passing in a newly allocated page (mcopy_atomic_pte()), whose page->mapping is not yet setup. However that's not extremely obvious either. For either of above, use page_mapping() instead. Link: https://lkml.kernel.org/r/Y2K+y7wnhC4vbnP2@x1n Fixes: 153132571f02 ("userfaultfd/shmem: support UFFDIO_CONTINUE for shmem") Signed-off-by: Peter Xu Reported-by: Matthew Wilcox Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Axel Rasmussen Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/userfaultfd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -63,7 +63,7 @@ int mfill_atomic_install_pte(struct mm_s pte_t _dst_pte, *dst_pte; bool writable = dst_vma->vm_flags & VM_WRITE; bool vm_shared = dst_vma->vm_flags & VM_SHARED; - bool page_in_cache = page->mapping; + bool page_in_cache = page_mapping(page); spinlock_t *ptl; struct inode *inode; pgoff_t offset, max_off;