perf tests: Fix out of bounds access on array fd when cnt is 100

Currently when cnt is 100 an array bounds overflow occurs on the
assignment of fd[cnt]. Fix this by performing the bounds check on cnt
before writing to fd.

Detected by cppcheck:

tools/perf/tests/bp_account.c:115: (warning) Either the condition
'cnt==100' is redundant or the array 'fd[100]' is accessed at index 100,
which is out of bounds.

Signed-off-by: Colin King <colin.king@canonical.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: kernel-janitors@vger.kernel.org
Fixes: 032db28e5fa3 ("perf tests: Add breakpoint accounting/modify test")
Link: http://lkml.kernel.org/r/20180314173354.11250-1-colin.king@canonical.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/tests/bp_account.c b/tools/perf/tests/bp_account.c
index 2f75fa0..9e88d76 100644 (file)
--- a/tools/perf/tests/bp_account.c
+++ b/tools/perf/tests/bp_account.c
@@ -107,16 +107,14 @@ static int detect_cnt(bool is_x)
        int fd[100], cnt = 0, i;
 
        while (1) {
-               fd[cnt] = __event(is_x, addr, &attr);
-
-               if (fd[cnt] < 0)
-                       break;
-
                if (cnt == 100) {
                        pr_debug("way too many debug registers, fix the test\n");
                        return 0;
                }
+               fd[cnt] = __event(is_x, addr, &attr);
 
+               if (fd[cnt] < 0)
+                       break;
                cnt++;
        }