[PATCH 2/2] perf iostat: Fix Segmentation fault from NULL 'struct perf_counts_values *'

Like Xu
2021-09-27T08:13:37Z

From: Like Xu <likexu@tencent.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@tencent.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