Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754977Ab3IIQC5 (ORCPT ); Mon, 9 Sep 2013 12:02:57 -0400 Received: from kanga.kvack.org ([205.233.56.17]:46144 "EHLO kanga.kvack.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753814Ab3IIQCz (ORCPT ); Mon, 9 Sep 2013 12:02:55 -0400 Date: Mon, 9 Sep 2013 12:02:53 -0400 From: Benjamin LaHaise To: Alexander Viro , Gu Zheng Cc: linux-aio@kvack.org, linux-fsdevel@kvack.org, Linux Kernel Subject: [PATCH aio-next] aio: fix race in ring buffer page lookup introduced by page migration support Message-ID: <20130909160253.GA11250@kvack.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.2.2i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2545 Lines: 68 Hi Al, Gu, I've added this patch to my tree at git://git.kvack.org/~bcrl/aio-next.git to fix the get_user_pages() issue introduced by Gu's changes in the page migration patch. Thanks Al for spotting this. -ben commit d6c355c7dabcd753a75bc77d150d36328a355267 Author: Benjamin LaHaise Date: Mon Sep 9 11:57:59 2013 -0400 aio: fix race in ring buffer page lookup introduced by page migration support Prior to the introduction of page migration support in "fs/aio: Add support to aio ring pages migration" / 36bc08cc01709b4a9bb563b35aa530241ddc63e3, mapping of the ring buffer pages was done via get_user_pages() while retaining mmap_sem held for write. This avoided possible races with userland racing an munmap() or mremap(). The page migration patch, however, switched to using mm_populate() to prime the page mapping. mm_populate() cannot be called with mmap_sem held. Instead of dropping the mmap_sem, revert to the old behaviour and simply drop the use of mm_populate() since get_user_pages() will cause the pages to get mapped anyways. Thanks to Al Viro for spotting this issue. Signed-off-by: Benjamin LaHaise diff --git a/fs/aio.c b/fs/aio.c index 6e26755..f4a27af 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -307,16 +307,25 @@ static int aio_setup_ring(struct kioctx *ctx) aio_free_ring(ctx); return -EAGAIN; } - up_write(&mm->mmap_sem); - - mm_populate(ctx->mmap_base, populate); pr_debug("mmap address: 0x%08lx\n", ctx->mmap_base); + + /* We must do this while still holding mmap_sem for write, as we + * need to be protected against userspace attempting to mremap() + * or munmap() the ring buffer. + */ ctx->nr_pages = get_user_pages(current, mm, ctx->mmap_base, nr_pages, 1, 0, ctx->ring_pages, NULL); + + /* Dropping the reference here is safe as the page cache will hold + * onto the pages for us. It is also required so that page migration + * can unmap the pages and get the right reference count. + */ for (i = 0; i < ctx->nr_pages; i++) put_page(ctx->ring_pages[i]); + up_write(&mm->mmap_sem); + if (unlikely(ctx->nr_pages != nr_pages)) { aio_free_ring(ctx); return -EAGAIN; -- "Thought is the essence of where you are now." -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/