linux-kernel - [PATCH 1/3] Fix backward-ring-buffer.c format-truncation error

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Message-Id: <20190724184512.162887-2-nums@google.com>
Date:   Wed, 24 Jul 2019 11:45:10 -0700
From:   Numfor Mbiziwo-Tiapo <nums@...gle.com>
To:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, songliubraving@...com, mbd@...com
Cc:     linux-kernel@...r.kernel.org, irogers@...gle.com,
        eranian@...gle.com, Numfor Mbiziwo-Tiapo <nums@...gle.com>
Subject: [PATCH 1/3] Fix backward-ring-buffer.c format-truncation error

Perf does not build with the ubsan (undefined behavior sanitizer)
and there is an error that says:

tests/backward-ring-buffer.c:23:45: error: ‘%d’ directive output
may be truncated writing between 1 and 10 bytes into a region of
size 8 [-Werror=format-truncation=]
   snprintf(proc_name, sizeof(proc_name), "p:%d\n", i);

This can be reproduced by running (from the tip directory):
make -C tools/perf USE_CLANG=1 EXTRA_CFLAGS="-fsanitize=undefined"

Th error occurs because they are writing to the 10 byte buffer - the
index 'i' of the for loop and the 2 byte hardcoded string. If somehow 'i'
was greater than 8 bytes (10 - 2), then the snprintf function would
truncate the string. Increasing the size of the buffer fixes the error.

Signed-off-by: Numfor Mbiziwo-Tiapo <nums@...gle.com>
---
 tools/perf/tests/backward-ring-buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/tests/backward-ring-buffer.c b/tools/perf/tests/backward-ring-buffer.c
index 6d598cc071ae..1a9c3becf5ff 100644
--- a/tools/perf/tests/backward-ring-buffer.c
+++ b/tools/perf/tests/backward-ring-buffer.c
@@ -18,7 +18,7 @@ static void testcase(void)
 	int i;
 
 	for (i = 0; i < NR_ITERS; i++) {
-		char proc_name[10];
+		char proc_name[15];
 
 		snprintf(proc_name, sizeof(proc_name), "p:%d\n", i);
 		prctl(PR_SET_NAME, proc_name);
-- 
2.22.0.657.g960e92d24f-goog