From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2167DC282C8 for ; Mon, 28 Jan 2019 15:50:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E4CBB2177E for ; Mon, 28 Jan 2019 15:50:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548690639; bh=9nWC3JFowFGkWzB9I/xs15Rrn20kXuOYgolTY3jvVyI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=qX+m58NacNqAbtRlG5uYaFUG3HOKBCsU/aEDk6xTzQinK0Cvezmq9raMLYAolbYAc 58hmMFuqy41uz/tEzzP83n+EL6hqiVD89tRY1VMb/3p5h1NhazZwMm5kJGPWbAVNKF dCyCYwnThLbRDaSaJrXB50UkxCrHCiX+ZIvOYZIE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728962AbfA1Pug (ORCPT ); Mon, 28 Jan 2019 10:50:36 -0500 Received: from mail.kernel.org ([198.145.29.99]:36900 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728953AbfA1Pud (ORCPT ); Mon, 28 Jan 2019 10:50:33 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EC8732175B; Mon, 28 Jan 2019 15:50:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548690633; bh=9nWC3JFowFGkWzB9I/xs15Rrn20kXuOYgolTY3jvVyI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=sucQC0YaNbANg8dfhPJkWRM0uUfA2Uebc6GMDS3j5pMxQa069P4HIOZeXvjZFrPtK X0hJ1XEB97s5qrwVZm4whyh63Tye668RX9oVOAUBN7V8twb3H01+/jDIsNU7rLCs2E cjQexmiB5uY2EQTOvasnjAvZ7Kca7p+2BeOXwNu0= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Dan Carpenter , Steven Rostedt , Sasha Levin Subject: [PATCH AUTOSEL 4.20 147/304] tracing: Have trace_stack nr_entries compare not be so subtle Date: Mon, 28 Jan 2019 10:41:04 -0500 Message-Id: <20190128154341.47195-147-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190128154341.47195-1-sashal@kernel.org> References: <20190128154341.47195-1-sashal@kernel.org> MIME-Version: 1.0 X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dan Carpenter [ Upstream commit ca16b0fbb05242f18da9d810c07d3882ffed831c ] Dan Carpenter reviewed the trace_stack.c code and figured he found an off by one bug. "From reviewing the code, it seems possible for stack_trace_max.nr_entries to be set to .max_entries and in that case we would be reading one element beyond the end of the stack_dump_trace[] array. If it's not set to .max_entries then the bug doesn't affect runtime." Although it looks to be the case, it is not. Because we have: static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] = { [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX }; struct stack_trace stack_trace_max = { .max_entries = STACK_TRACE_ENTRIES - 1, .entries = &stack_dump_trace[0], }; And: stack_trace_max.nr_entries = x; for (; x < i; x++) stack_dump_trace[x] = ULONG_MAX; Even if nr_entries equals max_entries, indexing with it into the stack_dump_trace[] array will not overflow the array. But if it is the case, the second part of the conditional that tests stack_dump_trace[nr_entries] to ULONG_MAX will always be true. By applying Dan's patch, it removes the subtle aspect of it and makes the if conditional slightly more efficient. Link: http://lkml.kernel.org/r/20180620110758.crunhd5bfep7zuiz@kili.mountain Signed-off-by: Dan Carpenter Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Sasha Levin --- kernel/trace/trace_stack.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c index 2b0d1ee3241c..e2a153fc1afc 100644 --- a/kernel/trace/trace_stack.c +++ b/kernel/trace/trace_stack.c @@ -286,7 +286,7 @@ __next(struct seq_file *m, loff_t *pos) { long n = *pos - 1; - if (n > stack_trace_max.nr_entries || stack_dump_trace[n] == ULONG_MAX) + if (n >= stack_trace_max.nr_entries || stack_dump_trace[n] == ULONG_MAX) return NULL; m->private = (void *)n; -- 2.19.1