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 5C96AC001E0 for ; Tue, 1 Aug 2023 09:51:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233715AbjHAJvO (ORCPT ); Tue, 1 Aug 2023 05:51:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50618 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233730AbjHAJvC (ORCPT ); Tue, 1 Aug 2023 05:51:02 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5DA56269D for ; Tue, 1 Aug 2023 02:50:31 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E1E15614DF for ; Tue, 1 Aug 2023 09:50:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDF6FC433C8; Tue, 1 Aug 2023 09:50:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1690883430; bh=P0cv7mtuM/xucLEWDgmSXOUo/dHnKUBWmknw7veC/7c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vcZlREsfgRqm3EcMds8Rgm8DzzHArjFdwXrP4m2AY5Hr8gh5AfdGcKXrtDsC1qcYk bmDRiWyB0xyDjI9z1kT4boTqqZXo4a7Grf1K0cy571CX2APVWRDykIszZVyCHSaLCL WZUITx6Ys3WK2ZfrU7J0sQySBtlX5zltV+CCh2Wk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jann Horn , Suren Baghdasaryan , Andrew Morton Subject: [PATCH 6.4 234/239] mm: lock VMA in dup_anon_vma() before setting ->anon_vma Date: Tue, 1 Aug 2023 11:21:38 +0200 Message-ID: <20230801091934.461315217@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230801091925.659598007@linuxfoundation.org> References: <20230801091925.659598007@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: Jann Horn commit d8ab9f7b644a2c9b64de405c1953c905ff219dc9 upstream. When VMAs are merged, dup_anon_vma() is called with `dst` pointing to the VMA that is being expanded to cover the area previously occupied by another VMA. This currently happens while `dst` is not write-locked. This means that, in the `src->anon_vma && !dst->anon_vma` case, as soon as the assignment `dst->anon_vma = src->anon_vma` has happened, concurrent page faults can happen on `dst` under the per-VMA lock. This is already icky in itself, since such page faults can now install pages into `dst` that are attached to an `anon_vma` that is not yet tied back to the `anon_vma` with an `anon_vma_chain`. But if `anon_vma_clone()` fails due to an out-of-memory error, things get much worse: `anon_vma_clone()` then reverts `dst->anon_vma` back to NULL, and `dst` remains completely unconnected to the `anon_vma`, even though we can have pages in the area covered by `dst` that point to the `anon_vma`. This means the `anon_vma` of such pages can be freed while the pages are still mapped into userspace, which leads to UAF when a helper like folio_lock_anon_vma_read() tries to look up the anon_vma of such a page. This theoretically is a security bug, but I believe it is really hard to actually trigger as an unprivileged user because it requires that you can make an order-0 GFP_KERNEL allocation fail, and the page allocator tries pretty hard to prevent that. I think doing the vma_start_write() call inside dup_anon_vma() is the most straightforward fix for now. For a kernel-assisted reproducer, see the notes section of the patch mail. Link: https://lkml.kernel.org/r/20230721034643.616851-1-jannh@google.com Fixes: 5e31275cc997 ("mm: add per-VMA lock and helper functions to control it") Signed-off-by: Jann Horn Reviewed-by: Suren Baghdasaryan Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/mmap.c | 1 + 1 file changed, 1 insertion(+) --- a/mm/mmap.c +++ b/mm/mmap.c @@ -647,6 +647,7 @@ static inline int dup_anon_vma(struct vm * anon pages imported. */ if (src->anon_vma && !dst->anon_vma) { + vma_start_write(dst); dst->anon_vma = src->anon_vma; return anon_vma_clone(dst, src); }