On Fri, Jul 24, 2015 at 02:45:56PM +0300, Alexander Shishkin wrote:
> +static void perf_error_report_site(struct perf_event_attr *attr,
> +                                const struct perf_err_site *site)
> +{
> +     void *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;
> +
> +     if (copy_to_user((void __user *)attr->perf_err, buffer,
> +                      attr->perf_err_size)) {

Should that not be min(attr->perf_err_size, strlen(buffer)) ?

Also, should we not '\0' the last char in attr->perf_err in case buffer
is longer.

> +             /* if we failed to copy once, don't bother later */
> +             attr->perf_err_size = 0;
> +     }

So we want update the user's perf_err_size with the actual size we
copied in?

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