Path: csiph.com!news.mixmin.net!news.unit0.net!news.panservice.it!bofh.it!news.nic.it!robomod From: lizf@kernel.org Newsgroups: linux.kernel Subject: [PATCH 3.4 061/125] fuse: break infinite loop in fuse_fill_write_pages() Date: Wed, 12 Oct 2016 15:00:03 +0200 Message-ID: References: X-Original-To: stable@vger.kernel.org X-Mailer: git-send-email 1.9.1 Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 64 Organization: linux.* mail to news gateway X-Original-Cc: linux-kernel@vger.kernel.org, Roman Gushchin , Andrew Morton , Maxim Patlasov , Konstantin Khlebnikov , Miklos Szeredi , Zefan Li X-Original-Date: Wed, 12 Oct 2016 20:32:57 +0800 X-Original-Message-ID: <1476275641-4697-61-git-send-email-lizf@kernel.org> X-Original-References: <1476275600-4626-1-git-send-email-lizf@kernel.org> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1499604 From: Roman Gushchin 3.4.113-rc1 review patch. If anyone has any objections, please let me know. ------------------ 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: Zefan Li --- 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 e4f1f1a..951457a 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -846,6 +846,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req, mark_page_accessed(page); + iov_iter_advance(ii, tmp); if (!tmp) { unlock_page(page); page_cache_release(page); @@ -857,7 +858,6 @@ 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; -- 1.9.1