[PATCH] perf: Fix crash due to null pointer dereference when iterating cpu map

[zhe.he]

From: He Zhe <zhe.he@xxxxxxxxxxxxx>

NULL pointer may be passed to perf_cpu_map__cpu and then cause the
following crash.

perf ftrace -G start_kernel ls
failed to set tracing filters
[  208.710716] perf[341]: segfault at 4 ip 00000000567c7c98
               sp 00000000ff937ae0 error 4 in perf[56630000+1b2000]
[  208.724778] Code: fc ff ff e8 aa 9b 01 00 8d b4 26 00 00 00 00 8d
                     76 00 55 89 e5 83 ec 18 65 8b 0d 14 00 00 00 89
                     4d f4 31 c9 8b 45 08 8b9
Segmentation fault

Program received signal SIGSEGV, Segmentation fault.
0x5677dc98 in perf_cpu_map__cpu (cpus=0x0, idx=0) at cpumap.c:250
250     cpumap.c: No such file or directory.
(gdb) bt
0  0x5677dc98 in perf_cpu_map__cpu (cpus=0x0, idx=0) at cpumap.c:250
1  0x566790bd in evlist__close (evlist=0x56a6f470) at util/evlist.c:1222
2  0x566792aa in evlist__delete (evlist=evlist@entry=0x56a6f470)
   at util/evlist.c:152
3  0x5667936b in evlist__delete (evlist=0x56a6f470) at util/evlist.c:148
4  0x565efd39 in cmd_ftrace (argc=1, argv=0xffffdd18) at builtin-ftrace.c:520
5  0x56660ee7 in run_builtin (p=0x56993004 <commands+324>, argc=4,
   argv=0xffffdd18) at perf.c:312
6  0x565e7fae in handle_internal_command (argv=<optimized out>,
   argc=<optimized out>) at perf.c:364
7  run_argv (argcp=<optimized out>, argv=<optimized out>) at perf.c:408
8  main (argc=<optimized out>, argv=<optimized out>) at perf.c:538

Add null pointer check for iteration and NULL assignment for all_cpus.
And there is no need to iterate if there is no cpus.

Signed-off-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
---
 tools/lib/perf/cpumap.c | 4 ++--
 tools/lib/perf/evlist.c | 1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/lib/perf/cpumap.c b/tools/lib/perf/cpumap.c
index f93f4e703e4c..128386647ac0 100644
--- a/tools/lib/perf/cpumap.c
+++ b/tools/lib/perf/cpumap.c
@@ -247,7 +247,7 @@ struct perf_cpu_map *perf_cpu_map__new(const char *cpu_list)
 
 int perf_cpu_map__cpu(const struct perf_cpu_map *cpus, int idx)
 {
-	if (idx < cpus->nr)
+	if (cpus && idx < cpus->nr)
 		return cpus->map[idx];
 
 	return -1;
@@ -255,7 +255,7 @@ int perf_cpu_map__cpu(const struct perf_cpu_map *cpus, int idx)
 
 int perf_cpu_map__nr(const struct perf_cpu_map *cpus)
 {
-	return cpus ? cpus->nr : 1;
+	return cpus ? cpus->nr : 0;
 }
 
 bool perf_cpu_map__empty(const struct perf_cpu_map *map)
diff --git a/tools/lib/perf/evlist.c b/tools/lib/perf/evlist.c
index ae9e65aa2491..d57adf3020fe 100644
--- a/tools/lib/perf/evlist.c
+++ b/tools/lib/perf/evlist.c
@@ -127,6 +127,7 @@ void perf_evlist__exit(struct perf_evlist *evlist)
 	perf_cpu_map__put(evlist->cpus);
 	perf_thread_map__put(evlist->threads);
 	evlist->cpus = NULL;
+	evlist->all_cpus = NULL;
 	evlist->threads = NULL;
 	fdarray__exit(&evlist->pollfd);
 }
-- 
2.24.1