From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753391AbcFEK3d (ORCPT ); Sun, 5 Jun 2016 06:29:33 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:22111 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753239AbcFEKYf (ORCPT ); Sun, 5 Jun 2016 06:24:35 -0400 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: "Steven Rostedt (Red Hat)" , stable@vger.kernel.org#3.5+, Willy Tarreau Subject: [PATCH 3.10 133/143] ring-buffer: Prevent overflow of size in ring_buffer_resize() Date: Sun, 5 Jun 2016 12:20:36 +0200 Message-Id: <1465122046-9645-134-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1465122046-9645-1-git-send-email-w@1wt.eu> References: <1465122046-9645-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Steven Rostedt (Red Hat)" commit 59643d1535eb220668692a5359de22545af579f6 upstream. If the size passed to ring_buffer_resize() is greater than MAX_LONG - BUF_PAGE_SIZE then the DIV_ROUND_UP() will return zero. Here's the details: # echo 18014398509481980 > /sys/kernel/debug/tracing/buffer_size_kb tracing_entries_write() processes this and converts kb to bytes. 18014398509481980 << 10 = 18446744073709547520 and this is passed to ring_buffer_resize() as unsigned long size. size = DIV_ROUND_UP(size, BUF_PAGE_SIZE); Where DIV_ROUND_UP(a, b) is (a + b - 1)/b BUF_PAGE_SIZE is 4080 and here 18446744073709547520 + 4080 - 1 = 18446744073709551599 where 18446744073709551599 is still smaller than 2^64 2^64 - 18446744073709551599 = 17 But now 18446744073709551599 / 4080 = 4521260802379792 and size = size * 4080 = 18446744073709551360 This is checked to make sure its still greater than 2 * 4080, which it is. Then we convert to the number of buffer pages needed. nr_page = DIV_ROUND_UP(size, BUF_PAGE_SIZE) but this time size is 18446744073709551360 and 2^64 - (18446744073709551360 + 4080 - 1) = -3823 Thus it overflows and the resulting number is less than 4080, which makes 3823 / 4080 = 0 an nr_pages is set to this. As we already checked against the minimum that nr_pages may be, this causes the logic to fail as well, and we crash the kernel. There's no reason to have the two DIV_ROUND_UP() (that's just result of historical code changes), clean up the code and fix this bug. Cc: stable@vger.kernel.org # 3.5+ Fixes: 83f40318dab00 ("ring-buffer: Make removal of ring buffer pages atomic") Signed-off-by: Steven Rostedt Signed-off-by: Willy Tarreau --- kernel/trace/ring_buffer.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 6f70235..c4ce3a9 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1644,14 +1644,13 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size, !cpumask_test_cpu(cpu_id, buffer->cpumask)) return size; - size = DIV_ROUND_UP(size, BUF_PAGE_SIZE); - size *= BUF_PAGE_SIZE; + nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE); /* we need a minimum of two pages */ - if (size < BUF_PAGE_SIZE * 2) - size = BUF_PAGE_SIZE * 2; + if (nr_pages < 2) + nr_pages = 2; - nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE); + size = nr_pages * BUF_PAGE_SIZE; /* * Don't succeed if resizing is disabled, as a reader might be -- 2.8.0.rc2.1.gbe9624a