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

[Li Zhang]

On 2015å06æ10æ 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@xxxxxxxxxxxxxxxxxx>
> > ---
> >   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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