Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932940AbcDBA5P (ORCPT ); Fri, 1 Apr 2016 20:57:15 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:54496 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932916AbcDBA46 (ORCPT ); Fri, 1 Apr 2016 20:56:58 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Rabin Vincent , Al Viro , Kamal Mostafa Subject: [PATCH 3.19.y-ckt 108/170] splice: handle zero nr_pages in splice_to_pipe() Date: Fri, 1 Apr 2016 17:53:14 -0700 Message-Id: <1459558456-24452-109-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1459558456-24452-1-git-send-email-kamal@canonical.com> References: <1459558456-24452-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.19 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2578 Lines: 73 3.19.8-ckt18 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Rabin Vincent commit d6785d9152147596f60234157da2b02540c3e60f upstream. Running the following command: busybox cat /sys/kernel/debug/tracing/trace_pipe > /dev/null with any tracing enabled pretty very quickly leads to various NULL pointer dereferences and VM BUG_ON()s, such as these: BUG: unable to handle kernel NULL pointer dereference at 0000000000000020 IP: [] generic_pipe_buf_release+0xc/0x40 Call Trace: [] splice_direct_to_actor+0x143/0x1e0 [] ? generic_pipe_buf_nosteal+0x10/0x10 [] do_splice_direct+0x8f/0xb0 [] do_sendfile+0x199/0x380 [] SyS_sendfile64+0x90/0xa0 [] entry_SYSCALL_64_fastpath+0x12/0x6d page dumped because: VM_BUG_ON_PAGE(atomic_read(&page->_count) == 0) kernel BUG at include/linux/mm.h:367! invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC RIP: [] generic_pipe_buf_release+0x3c/0x40 Call Trace: [] splice_direct_to_actor+0x143/0x1e0 [] ? generic_pipe_buf_nosteal+0x10/0x10 [] do_splice_direct+0x8f/0xb0 [] do_sendfile+0x199/0x380 [] SyS_sendfile64+0x90/0xa0 [] tracesys_phase2+0x84/0x89 (busybox's cat uses sendfile(2), unlike the coreutils version) This is because tracing_splice_read_pipe() can call splice_to_pipe() with spd->nr_pages == 0. spd_pages underflows in splice_to_pipe() and we fill the page pointers and the other fields of the pipe_buffers with garbage. All other callers of splice_to_pipe() avoid calling it when nr_pages == 0, and we could make tracing_splice_read_pipe() do that too, but it seems reasonable to have splice_to_page() handle this condition gracefully. Signed-off-by: Rabin Vincent Reviewed-by: Christoph Hellwig Signed-off-by: Al Viro Signed-off-by: Kamal Mostafa --- fs/splice.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/splice.c b/fs/splice.c index c4b93e4..f28c53b 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -186,6 +186,9 @@ ssize_t splice_to_pipe(struct pipe_inode_info *pipe, unsigned int spd_pages = spd->nr_pages; int ret, do_wakeup, page_nr; + if (!spd_pages) + return 0; + ret = 0; do_wakeup = 0; page_nr = 0; -- 2.7.4