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Re: [PATCH] perf report: Fix a memory corrupton issue when enabling --branch-history






On 2/13/2018 5:45 PM, Jiri Olsa wrote:
On Tue, Feb 13, 2018 at 04:44:28PM +0800, Jin Yao wrote:
Following command lines will cause perf crash.

perf record -j call -g -a <application>
perf report --branch-history

*** Error in `perf': double free or corruption (!prev): 0x00000000104aa040 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x77725)[0x7f6b37254725]
/lib/x86_64-linux-gnu/libc.so.6(+0x7ff4a)[0x7f6b3725cf4a]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7f6b37260abc]
perf[0x51b914]
perf(hist_entry_iter__add+0x1e5)[0x51f305]
perf[0x43cf01]
perf[0x4fa3bf]
perf[0x4fa923]
perf[0x4fd396]
perf[0x4f9614]
perf(perf_session__process_events+0x89e)[0x4fc38e]
perf(cmd_report+0x15d2)[0x43f202]
perf[0x4a059f]
perf(main+0x631)[0x427b71]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7f6b371fd830]
perf(_start+0x29)[0x427d89]

The memory corruption happens at:

iter_add_next_cumulative_entry()
{
         ...
         for (i = 0; i < iter->curr; i++) {
         ...
}

Whatever in iter_next_cumulative_entry() or in iter_add_next_cumulative_entry(),
they all don't check if iter->curr exceeds the array 'he_cache[]'.

If there are too many nodes in callchain, it's possible that iter->curr >
iter->max_stack, then memory corruption occurs.

This patch will reallocate array 'he_cache[]' in iter_next_cumulative_entry()
if necessary (the case of too many nodes in callchain).

right, the max_stack does not say how many nodes end up in
callchain_cursor at the end.. good catch, please mention
that also in the changelog


max_stack looks only to limit the number of calls but not for other branches.

however we know the final count from callchain_cursor itself,
the attached patch might do the same job, right?


I think the attached patch is ok.

also could we now get rid of iter->max_stack?


From my opinion, the option '--max-stack' in perf report looks not very necessary. While it's just my personal opinion, need to hear from more people. :)

Thanks
Jin Yao

thanks,
jirka


---
diff --git a/tools/perf/util/hist.c b/tools/perf/util/hist.c
index b6140950301e..b50b7b70dcca 100644
--- a/tools/perf/util/hist.c
+++ b/tools/perf/util/hist.c
@@ -879,7 +879,7 @@ iter_prepare_cumulative_entry(struct hist_entry_iter *iter,
  	 * cumulated only one time to prevent entries more than 100%
  	 * overhead.
  	 */
-	he_cache = malloc(sizeof(*he_cache) * (iter->max_stack + 1));
+	he_cache = malloc(sizeof(*he_cache) * (callchain_cursor.nr + 1));
  	if (he_cache == NULL)
  		return -ENOMEM;