From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, hujianyang , Laurence Withers , Artem Bityutskiy Subject: [PATCH 3.15 17/66] UBIFS: fix an mmap and fsync race condition Date: Fri, 4 Jul 2014 15:14:16 -0700 Message-Id: <20140704221423.615890751@linuxfoundation.org> In-Reply-To: <20140704221422.813435485@linuxfoundation.org> References: <20140704221422.813435485@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: hujianyang commit 691a7c6f28ac90cccd0dbcf81348ea90b211bdd0 upstream. There is a race condition in UBIFS: Thread A (mmap) Thread B (fsync) ->__do_fault ->write_cache_pages -> ubifs_vm_page_mkwrite -> budget_space -> lock_page -> release/convert_page_budget -> SetPagePrivate -> TestSetPageDirty -> unlock_page -> lock_page -> TestClearPageDirty -> ubifs_writepage -> do_writepage -> release_budget -> ClearPagePrivate -> unlock_page -> !(ret & VM_FAULT_LOCKED) -> lock_page -> set_page_dirty -> ubifs_set_page_dirty -> TestSetPageDirty (set page dirty without budgeting) -> unlock_page This leads to situation where we have a diry page but no budget allocated for this page, so further write-back may fail with -ENOSPC. In this fix we return from page_mkwrite without performing unlock_page. We return VM_FAULT_LOCKED instead. After doing this, the race above will not happen. Signed-off-by: hujianyang Tested-by: Laurence Withers Signed-off-by: Artem Bityutskiy Signed-off-by: Greg Kroah-Hartman --- fs/ubifs/file.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/fs/ubifs/file.c +++ b/fs/ubifs/file.c @@ -1525,8 +1525,7 @@ static int ubifs_vm_page_mkwrite(struct } wait_for_stable_page(page); - unlock_page(page); - return 0; + return VM_FAULT_LOCKED; out_unlock: unlock_page(page);