linux-kernel - Re: [PATCH v2 1/6] perf: Introduce extended syscall error reporting

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Message-ID: <87vbbu63vu.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Tue, 01 Sep 2015 09:38:13 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Vince Weaver <vince@...ter.net>,
	Stephane Eranian <eranian@...gle.com>,
	Johannes Berg <johannes@...solutions.net>
Subject: Re: [PATCH v2 1/6] perf: Introduce extended syscall error reporting

Andy Shevchenko <andy.shevchenko@...il.com> writes:

> On Mon, Aug 24, 2015 at 5:32 PM, Alexander Shishkin
> <alexander.shishkin@...ux.intel.com> wrote:
>> +       /* trim the buffer to the supplied boundary */
>> +       len = strlen(buffer);
>> +       if (len >= attr->perf_err_size) {
>> +               len = attr->perf_err_size - 1;
>> +               buffer[len] = 0;
>> +       }
>
> len = strnlen(buffer, attr->perf_err_size);
> buffer[len] = 0;
>
> And perhaps perf_err_size has to be length (perf_err_len) ?
>
>> +
>> +       if (copy_to_user((void __user *)attr->perf_err, buffer, len + 1)) {
>> +               /* if we failed to copy once, don't bother later */
>> +               attr->perf_err_size = 0;
>
> Kaboom next time on buffer[-1] = 0; since len >= 0?

Of course, we never get here if attr::perf_err_size is 0, there's an
explicit check for that, but nice try.

Regards,
--
Alex
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