linux-kernel - [PATCH 02/14] perf tests: Fix out of bounds access on array fd when cnt is 100

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Date:   Mon, 19 Mar 2018 16:01:24 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Colin Ian King <colin.king@...onical.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        kernel-janitors@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 02/14] perf tests: Fix out of bounds access on array fd when cnt is 100

From: Colin Ian King <colin.king@...onical.com>

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@...onical.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: kernel-janitors@...r.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@...hat.com>
---
 tools/perf/tests/bp_account.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/tools/perf/tests/bp_account.c b/tools/perf/tests/bp_account.c
index 2f75fa0c4fef..9e88d7608951 100644
--- 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++;
 	}
 
-- 
2.14.3