linux-kernel - [PATCH 2/2] perf iostat: Fix Segmentation fault from NULL 'struct perf_counts

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Date:   Mon, 27 Sep 2021 16:11:15 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ian Rogers <irogers@...gle.com>
Cc:     Alexander Antonov <alexander.antonov@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Stephane Eranian <eranian@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] perf iostat: Fix Segmentation fault from NULL 'struct perf_counts_values *'

From: Like Xu <likexu@...cent.com>

If the perf-iostat user specifies two or more iio_root_ports and
also specifies the cpu(s) by -C which is not *connected to all*
the above iio ports, the iostat_print_metric() will run into trouble:

For example:

 $ perf iostat list
 S0-uncore_iio_0<0000:16>
 S1-uncore_iio_0<0000:97> # <--- CPU 1 is located in the socket S0

 $ perf iostat 0000:16,0000:97 -C 1 -- ls
 port 	Inbound Read(MB)	Inbound Write(MB)	Outbound Read(MB)	Outbound
 Write(MB) ../perf-iostat: line 12: 104418 Segmentation fault
 (core dumped) perf stat --iostat$DELIMITER$*

The core-dump stack says, in the above corner case, the returned
(struct perf_counts_values *) count will be NULL, and the caller
iostat_print_metric() apparently doesn't not handle this case.

 433	struct perf_counts_values *count = perf_counts(evsel->counts, die, 0);
 434
 435	if (count->run && count->ena) {
 (gdb) p count
 $1 = (struct perf_counts_values *) 0x0

The deeper reason is that there are actually no statistics from the user
specified pair "iostat 0000:X, -C (disconnected) Y ", but let's fix it with
minimum cost by adding a NULL check in the user space.

Signed-off-by: Like Xu <likexu@...cent.com>
---
 tools/perf/arch/x86/util/iostat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/arch/x86/util/iostat.c b/tools/perf/arch/x86/util/iostat.c
index eeafe97b8105..792cd75ade33 100644
--- a/tools/perf/arch/x86/util/iostat.c
+++ b/tools/perf/arch/x86/util/iostat.c
@@ -432,7 +432,7 @@ void iostat_print_metric(struct perf_stat_config *config, struct evsel *evsel,
 	u8 die = ((struct iio_root_port *)evsel->priv)->die;
 	struct perf_counts_values *count = perf_counts(evsel->counts, die, 0);
 
-	if (count->run && count->ena) {
+	if (count && count->run && count->ena) {
 		if (evsel->prev_raw_counts && !out->force_header) {
 			struct perf_counts_values *prev_count =
 				perf_counts(evsel->prev_raw_counts, die, 0);
-- 
2.32.0