Re: [PATCH v2] perf tests: Fix out of bounds memory access

[Jiri Olsa <jolsa@redhat.com>]

On Thu, Nov 07, 2019 at 10:02:44AM +0800, Leo Yan wrote:
> The test case 'Read backward ring buffer' failed on 32-bit architectures
> which were found by LKFT perf testing.  The test failed on arm32 x15
> device, qemu_arm32, qemu_i386, and found intermittent failure on i386;
> the failure log is as below:
> 
>   50: Read backward ring buffer                  :
>   --- start ---
>   test child forked, pid 510
>   Using CPUID GenuineIntel-6-9E-9
>   mmap size 1052672B
>   mmap size 8192B
>   Finished reading overwrite ring buffer: rewind
>   free(): invalid next size (fast)
>   test child interrupted
>   ---- end ----
>   Read backward ring buffer: FAILED!
> 
> The log hints there have issue for memory usage, thus free() reports
> error 'invalid next size' and directly exit for the case.  Finally, this
> issue is root caused as out of bounds memory access for the data array
> 'evsel->id'.
> 
> The backward ring buffer test invokes do_test() twice.  'evsel->id' is
> allocated at the first call with the flow:
> 
>   test__backward_ring_buffer()
>     `-> do_test()
> 	  `-> evlist__mmap()
> 	        `-> evlist__mmap_ex()
> 	              `-> perf_evsel__alloc_id()
> 
> So 'evsel->id' is allocated with one item, and it will be used in
> function perf_evlist__id_add():
> 
>    evsel->id[0] = id
>    evsel->ids   = 1
> 
> At the second call for do_test(), it skips to initialize 'evsel->id'
> and reuses the array which is allocated in the first call.  But
> 'evsel->ids' contains the stale value.  Thus:
> 
>    evsel->id[1] = id    -> out of bound access
>    evsel->ids   = 2
> 
> To fix this issue, we will use evlist__open() and evlist__close() pair
> functions to prepare and cleanup context for evlist; so 'evsel->id' and
> 'evsel->ids' can be initialized properly when invoke do_test() and avoid
> the out of bounds memory access.

right, we need to solve this on libperf level, so it's possible
to call mmap/munmap multiple time without close/open.. I'll try
to send something, but meanwhile this is good workaround

Reviewed-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka

> 
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
>  tools/perf/tests/backward-ring-buffer.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/tools/perf/tests/backward-ring-buffer.c b/tools/perf/tests/backward-ring-buffer.c
> index 338cd9faa835..5128f727c0ef 100644
> --- a/tools/perf/tests/backward-ring-buffer.c
> +++ b/tools/perf/tests/backward-ring-buffer.c
> @@ -147,6 +147,15 @@ int test__backward_ring_buffer(struct test *test __maybe_unused, int subtest __m
>  		goto out_delete_evlist;
>  	}
>  
> +	evlist__close(evlist);
> +
> +	err = evlist__open(evlist);
> +	if (err < 0) {
> +		pr_debug("perf_evlist__open: %s\n",
> +			 str_error_r(errno, sbuf, sizeof(sbuf)));
> +		goto out_delete_evlist;
> +	}
> +
>  	err = do_test(evlist, 1, &sample_count, &comm_count);
>  	if (err != TEST_OK)
>  		goto out_delete_evlist;
> -- 
> 2.17.1
>