[tip:perf/core] perf tests: Fix out of bounds access on array fd when cnt is 100

[tip-bot for Colin Ian King]

Commit-ID:  66790bc8e1f51831d73691954ae0b430bde614ad
Gitweb:     https://git.kernel.org/tip/66790bc8e1f51831d73691954ae0b430bde614ad
Author:     Colin Ian King <colin.king@xxxxxxxxxxxxx>
AuthorDate: Wed, 14 Mar 2018 17:33:54 +0000
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Fri, 16 Mar 2018 13:56:44 -0300

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@xxxxxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: kernel-janitors@xxxxxxxxxxxxxxx
Fixes: 032db28e5fa3 ("perf tests: Add breakpoint accounting/modify test")
Link: http://lkml.kernel.org/r/20180314173354.11250-1-colin.king@xxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 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++;
 	}