From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752586AbbFRF5F (ORCPT ); Thu, 18 Jun 2015 01:57:05 -0400 Received: from e18.ny.us.ibm.com ([129.33.205.208]:52897 "EHLO e18.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752465AbbFRF47 (ORCPT ); Thu, 18 Jun 2015 01:56:59 -0400 X-Helo: d01dlp01.pok.ibm.com X-MailFrom: sukadev@linux.vnet.ibm.com X-RcptTo: linux-kernel@vger.kernel.org Date: Wed, 17 Jun 2015 22:56:08 -0700 From: Sukadev Bhattiprolu To: Li Zhang Cc: acme@kernel.org, mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/1] perf tools: Check access permission when reading /proc/kcore file. Message-ID: <20150618055608.GA2193@us.ibm.com> References: <1434350500-32342-1-git-send-email-zhlcindy@linux.vnet.ibm.com> <20150617060946.GA18162@us.ibm.com> <55823B78.3050403@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55823B78.3050403@linux.vnet.ibm.com> X-Operating-System: Linux 2.0.32 on an i486 User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15061805-0045-0000-0000-0000007B63FE Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Li Zhang [zhlcindy@linux.vnet.ibm.com] wrote: | >For consistency with rest of the file, use pr_warning() or pr_err(). | | ui_warning can report the message to users directly when this | program is running. | But if we considered the consistency, pr_warning or pr_err should be better. | And users can get this message by trying another time. That seems to be the way perf currently operates - silent by default for non-fatal errors. -v or -vvv increases verbosity and reports non-fatal warnings/errors also. | | > | >Also, we could drop the access() call and report the error when open() | >fails below? | | I think we can drop this access. But /proc/kcore also require the | process with CAP_SYS_RAWIO | capability. Even if chown this file, access report right result, but | open still fails. Maybe the error message could hint that CAP_SYS_RAWIO would be needed. | | > | >| fd = open(kcore_filename, O_RDONLY); | >| if (fd < 0) | >| return -EINVAL; | > | >Further, if user specifies the file with --kallsyms and we are not | >able to read it, we should treat it as a fatal error and exit - this | >would be easer when parsing command line args. | I have another patch which checks this files. I will merge it to this patch. | | > | >If user did not specify the option and we are proactively trying to | >use /proc/kcore, we should not treat errors as fatal? i.e report | >a warning message and continue without symbols? | | In the current program, even if open fails, the program still | continue to run. | Is it helpful for users to get the address without symbols? Well, if profiling applications, user may not care about kernel symbols, so being unable to open /proc/kcore would be ok? If OTOH, user specifies --kallsyms, then they care about the kenrel symbols so we should treat the open() error () as fatal.