From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754468AbcAWO4z (ORCPT ); Sat, 23 Jan 2016 09:56:55 -0500 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:27541 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753565AbcAWOq4 (ORCPT ); Sat, 23 Jan 2016 09:46:56 -0500 Message-Id: <20160123141222.586450489@1wt.eu> User-Agent: quilt/0.63-1 Date: Sat, 23 Jan 2016 15:12:35 +0100 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Andrew Morton , Maxim Patlasov , Konstantin Khlebnikov , Roman Gushchin , Miklos Szeredi , Ben Hutchings , Willy Tarreau Subject: [PATCH 2.6.32 14/42] fuse: break infinite loop in fuse_fill_write_pages() MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.32-longterm 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: Ben Hutchings (cherry picked from commit a5b234167a1ff46f311f5835828eec2f971b9bb4) [wt: adjusted context, as commit 478e0841b from 3.1 was never backported to call mark_page_accessed() eventhough it seems it should have been] Signed-off-by: Willy Tarreau --- fs/fuse/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 102d582..c8dc4f3 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -885,6 +885,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req, pagefault_enable(); flush_dcache_page(page); + iov_iter_advance(ii, tmp); if (!tmp) { unlock_page(page); page_cache_release(page); @@ -896,7 +897,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req, req->pages[req->num_pages] = page; req->num_pages++; - iov_iter_advance(ii, tmp); count += tmp; pos += tmp; offset += tmp; -- 1.7.12.2.21.g234cd45.dirty