perf tools kvm: Fix the potential out of range memory access issue

kvm_add_default_arch_event() helper may add 2 extra options but it
directly modifies the original argv[] array. This may cause out of range
memory access. Fix this issue.

Signed-off-by: Dapeng Mi <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-kvm.c

···
 	int rec_argc, i = 0, j, ret;
 	const char **rec_argv;
 
-	ret = kvm_add_default_arch_event(&argc, argv);
-	if (ret)
-		return -EINVAL;
-
-	rec_argc = argc + 2;
+	/*
+	 * Besides the 2 more options "-o" and "filename",
+	 * kvm_add_default_arch_event() may add 2 extra options,
+	 * so allocate 4 more items.
+	 */
+	rec_argc = argc + 2 + 2;
 	rec_argv = calloc(rec_argc + 1, sizeof(char *));
 	if (!rec_argv)
 		return -ENOMEM;
···
 		rec_argv[i] = STRDUP_FAIL_EXIT(argv[j]);
 
 	BUG_ON(i != rec_argc);
+
+	ret = kvm_add_default_arch_event(&i, rec_argv);
+	if (ret)
+		goto EXIT;
 
 	ret = cmd_record(i, rec_argv);