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

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Date:	Mon, 15 Jun 2015 10:24:31 +0800
From:	Li Zhang <zhlcindy@...ux.vnet.ibm.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
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.

On 2015年06月10日 22:44, Arnaldo Carvalho de Melo wrote:
> 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.

This sounds much better. I will check whether it can deliver this 
message to user.

Thanks Li

>
> - 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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-- 

Li Zhang
IBM China Linux Technology Centre

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