[PATCH v2] perf ordered_events: fix crash in free_dup_event()

[Stephane Eranian]

This patch fixes a bug in ordered_event.c:alloc_event().
An ordered_event struct was not initialized properly potentially
causing crashes later on in free_dup_event() depending on the
content of the memory. If it was NULL, then it would work fine,
otherwise, it could cause crashes such as:

$ perf record -o - -e cycles date |  perf inject -b -i - >/dev/null
Tue Aug  7 12:03:48 PDT 2018
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.000 MB - ]
Segmentation fault (core dumped):

(gdb) r inject -b -i - < tt  >/dev/null
Program received signal SIGSEGV, Segmentation fault.
free_dup_event (oe=0x26a39a0, event=0xffffffff00000000) at util/ordered-events.c:85
(gdb) bt
#0  free_dup_event (oe=0x26a39a0, event=0xffffffff00000000) at util/ordered-events.c:85
#1  ordered_events__free (oe=0x26a39a0) at util/ordered-events.c:310
#2  0x00000000004b5a56 in __perf_session__process_pipe_events (session=<optimized out>) at util/session.c:1753
#3  perf_session__process_events (session=<optimized out>) at util/session.c:1932
#4  0x000000000043a2eb in __cmd_inject (inject=<optimized out>) at builtin-inject.c:750
#5  cmd_inject (argc=<optimized out>, argv=<optimized out>) at builtin-inject.c:924
#6  0x000000000046b175 in run_builtin (p=0xabc640 <commands+576>, argc=4, argv=0x7fffffffe560) at perf.c:297
#7  0x000000000046b062 in handle_internal_command (argc=4, argv=0x7fffffffe560) at perf.c:349
#8  0x000000000046a5e8 in run_argv (argcp=<optimized out>, argv=<optimized out>) at perf.c:393
#9  main (argc=4, argv=0x7fffffffe560) at perf.c:531

Signed-off-by: Stephane Eranian <eranian@xxxxxxxxxx>

---
 tools/perf/util/ordered-events.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/perf/util/ordered-events.c b/tools/perf/util/ordered-events.c
index a90dbe5df019..95c91e5a3754 100644
--- a/tools/perf/util/ordered-events.c
+++ b/tools/perf/util/ordered-events.c
@@ -118,6 +118,12 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
 
 		pr("alloc size %" PRIu64 "B (+%zu), max %" PRIu64 "B\n",
 		   oe->cur_alloc_size, size, oe->max_alloc_size);
+		/*
+		 * must initialize event pointer of commandeered first
+		 * entry to avoid crash in free_dup_event() due to random
+		 * value for this field.
+		 */
+		oe->buffer->event = NULL;
 
 		oe->cur_alloc_size += size;
 		list_add(&oe->buffer->list, &oe->to_free);
-- 
2.18.0.597.ga71716f1ad-goog