linux-kernel - Re: [PATCH 1/1] perf tools: Check access permission when reading /proc/kcore file.

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Date:	Wed, 10 Jun 2015 11:44:52 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Li Zhang <zhlcindy@...ux.vnet.ibm.com>
Cc:	mingo@...hat.com, sukadev@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] perf tools: Check access permission when reading
 /proc/kcore file.

Em Wed, Jun 10, 2015 at 11:01:33AM +0800, Li Zhang escreveu:
> When using command perf report --kallsyms=/proc/kallsyms with a non-root
> user, symbols are resolved. Then select one symbol and annotate it, it
> reports the error as the following:
> Can't annotate __clear_user: No vmlinux file with build id xxx was found.
> 
> The problem is caused by reading /proc/kcore without access permission.
> It needs to change access permission to allow a specific user to read 
> /proc/kcore or use root to execute the perf command.

But then only if the user tries it again, using -v to enable verbose
mode is that the message will be presented, how about instead return
-EPERM, or -errno, so that this error is propagated back and we
eventually emit a more meaningful message to the user, such as:

  "Insufficient permission to access %s.", kcore_filename

Trying to check if that is possible by going to the dso__load_kcore()
callers and on back to the tools.

- Arnaldo

> This patch is to check access permission when reading kcore file.
> 
> Signed-off-by: Li Zhang <zhlcindy@...ux.vnet.ibm.com>
> ---
>  tools/perf/util/symbol.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 201f6c4c..8255556 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -1125,6 +1125,11 @@ static int dso__load_kcore(struct dso *dso, struct map *map,
>  	md.type = map->type;
>  	INIT_LIST_HEAD(&md.maps);
>  
> +	if (access(kcore_filename, R_OK)) {
> +		pr_debug("Can't access file %s.\n", kcore_filename);
> +		return -EINVAL;
> +	}
> +
>  	fd = open(kcore_filename, O_RDONLY);
>  	if (fd < 0)
>  		return -EINVAL;
> -- 
> 2.1.0
--
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