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

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Date:	Mon, 31 Aug 2015 21:47:19 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.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

On Mon, Aug 24, 2015 at 5:32 PM, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:

One small comment below.

> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -49,6 +49,79 @@
>
>  #include <asm/irq_regs.h>
>
> +static bool extended_reporting_enabled(struct perf_event_attr *attr)
> +{
> +       if (attr->size >= PERF_ATTR_SIZE_VER6 &&
> +           attr->perf_err_size > 0)
> +               return true;
> +
> +       return false;
> +}
> +
> +/*
> + * Provide a JSON formatted error report to the user if they asked for it.
> + */
> +static void perf_error_report_site(struct perf_event_attr *attr,
> +                                  const struct perf_err_site *site)
> +{
> +       unsigned long len;
> +       char *buffer;
> +
> +       if (!site || !extended_reporting_enabled(attr))
> +               return;
> +
> +       /* in case of nested perf_err()s, which you shouldn't really do */
> +       while (site->code <= -PERF_ERRNO)
> +               site = perf_errno_to_site(site->code);
> +
> +       buffer = kasprintf(GFP_KERNEL,
> +                          "{\n"
> +                          "\t\"code\": %d,\n"
> +                          "\t\"module\": \"%s\",\n"
> +                          "\t\"message\": \"%s\"\n"
> +                          "}\n",
> +                          site->code, site->owner, site->message
> +                          );
> +       if (!buffer)
> +               return;
> +
> +       /* 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?

> +       }
> +
> +       kfree(buffer);
> +}

-- 
With Best Regards,
Andy Shevchenko
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