Re: [PATCH] perf evsel: fix NULL pointer deference when evsel->counts is NULL

[Namhyung Kim <namhyung@kernel.org>]

Hi Colin,

On Sat, 19 Jan 2013 16:36:54 +0000, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
>
> __perf_evsel__read_on_cpu() only bails out with -ENOMEM if
> evsel->counts is NULL and perf_evsel__alloc_counts() has returned
> an error.  If perf_evsel__alloc_counts() does not return an error
> we get an NULL pointer deference on evsel->counts->cpu[cpu]
> if evsel->counts is NULL.

perf_evsel__alloc_counts() should allocate evsel->counts when it sees
evsel->counts is NULL and return negative error code if the allocation
fails.

So I don't see any problem in current code.  With your code, it won't
try to allocate if ->counts is NULL but overwrite existing ->counts?

Thanks,
Namhyung

>
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  tools/perf/util/evsel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 1b16dd1..93acd06 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -640,7 +640,7 @@ int __perf_evsel__read_on_cpu(struct perf_evsel *evsel,
>  	if (FD(evsel, cpu, thread) < 0)
>  		return -EINVAL;
>  
> -	if (evsel->counts == NULL && perf_evsel__alloc_counts(evsel, cpu + 1) < 0)
> +	if (evsel->counts == NULL || perf_evsel__alloc_counts(evsel, cpu + 1) < 0)
>  		return -ENOMEM;
>  
>  	if (readn(FD(evsel, cpu, thread), &count, nv * sizeof(u64)) < 0)