From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932834AbcBXEYX (ORCPT ); Tue, 23 Feb 2016 23:24:23 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:53940 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755579AbcBXEYT (ORCPT ); Tue, 23 Feb 2016 23:24:19 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andrew Morton , Maxim Patlasov , Konstantin Khlebnikov , Roman Gushchin , Miklos Szeredi Subject: [PATCH 3.10 36/54] fuse: break infinite loop in fuse_fill_write_pages() Date: Tue, 23 Feb 2016 19:33:53 -0800 Message-Id: <20160224033353.865967404@linuxfoundation.org> X-Mailer: git-send-email 2.7.1 In-Reply-To: <20160224033352.613205610@linuxfoundation.org> References: <20160224033352.613205610@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Roman Gushchin commit 3ca8138f014a913f98e6ef40e939868e1e9ea876 upstream. I got a report about unkillable task eating CPU. Further investigation shows, that the problem is in the fuse_fill_write_pages() function. If iov's first segment has zero length, we get an infinite loop, because we never reach iov_iter_advance() call. Fix this by calling iov_iter_advance() before repeating an attempt to copy data from userspace. A similar problem is described in 124d3b7041f ("fix writev regression: pan hanging unkillable and un-straceable"). If zero-length segmend is followed by segment with invalid address, iov_iter_fault_in_readable() checks only first segment (zero-length), iov_iter_copy_from_user_atomic() skips it, fails at second and returns zero -> goto again without skipping zero-length segment. Patch calls iov_iter_advance() before goto again: we'll skip zero-length segment at second iteraction and iov_iter_fault_in_readable() will detect invalid address. Special thanks to Konstantin Khlebnikov, who helped a lot with the commit description. Cc: Andrew Morton Cc: Maxim Patlasov Cc: Konstantin Khlebnikov Signed-off-by: Roman Gushchin Signed-off-by: Miklos Szeredi Fixes: ea9b9907b82a ("fuse: implement perform_write") Signed-off-by: Greg Kroah-Hartman --- fs/fuse/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -993,6 +993,7 @@ static ssize_t fuse_fill_write_pages(str mark_page_accessed(page); + iov_iter_advance(ii, tmp); if (!tmp) { unlock_page(page); page_cache_release(page); @@ -1005,7 +1006,6 @@ static ssize_t fuse_fill_write_pages(str req->page_descs[req->num_pages].length = tmp; req->num_pages++; - iov_iter_advance(ii, tmp); count += tmp; pos += tmp; offset += tmp;