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

[Arnaldo Carvalho de Melo]

Em Thu, Mar 05, 2020 at 06:47:19PM +0800, zhe.he@xxxxxxxxxxxxx escreveu:
> 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

I'm not being able to repro this here, what is the tree you are using?

- Arnaldo
 
> 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