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=unavailable 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 460A5C282C8 for ; Mon, 28 Jan 2019 16:47:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 16BC62084C for ; Mon, 28 Jan 2019 16:47:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548694062; bh=qLnbqiT9riauDfqU+6LCamqrNi58n5MPx5SdsEi67lI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=GBxoNHSbj8v2UUuu84behPOmv1lI2rjTcIg3hihe2cH0BHZv/VRUulhfIiO9viKAo 7eGArIdl6c3GPvtj2m+c2/pI5z87GNgmScrJIKFyypMk1h8Ubs7u1IiQT6dc1tlj+g QADDrj6ULhrdem/tvum01pmYU1HniIyi9T58StjU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389136AbfA1QWD (ORCPT ); Mon, 28 Jan 2019 11:22:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:57822 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389073AbfA1QVz (ORCPT ); Mon, 28 Jan 2019 11:21:55 -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 26E912084A; Mon, 28 Jan 2019 16:21:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548692515; bh=qLnbqiT9riauDfqU+6LCamqrNi58n5MPx5SdsEi67lI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UyzOnRhD0k0XNRB5IJ+v93yb5LqZ/u9h6RS+eCZjU9BfR/i3Jal4wNuTIsNlnLwUH hNV2IfTEobxVVBTSBS/fmQf+1Yu/ObBvxqv1cv+FkRftHEx+Fsj3ygHsFlesW6o84G It7JFJzVDRby47678Tcxrz1Tv3D89XlEA/zV1ibI= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Dan Carpenter , Steven Rostedt , Sasha Levin Subject: [PATCH AUTOSEL 4.9 046/107] tracing: Have trace_stack nr_entries compare not be so subtle Date: Mon, 28 Jan 2019 11:18:46 -0500 Message-Id: <20190128161947.57405-46-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190128161947.57405-1-sashal@kernel.org> References: <20190128161947.57405-1-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 2a1abbaca10e..f9255740411e 100644 --- a/kernel/trace/trace_stack.c +++ b/kernel/trace/trace_stack.c @@ -290,7 +290,7 @@ __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