netdev - [iproute2 PATCH 2/2] bpf: Fixes a snprintf truncation warning

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Date:   Tue, 26 May 2020 18:04:11 +0200
From:   Andrea Claudi <aclaudi@...hat.com>
To:     netdev@...r.kernel.org
Cc:     stephen@...workplumber.org, dsahern@...il.com, jhs@...atatu.com
Subject: [iproute2 PATCH 2/2] bpf: Fixes a snprintf truncation warning

gcc v9.3.1 reports:

bpf.c: In function ‘bpf_get_work_dir’:
bpf.c:784:49: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
  784 |  snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
      |                                                 ^
bpf.c:784:2: note: ‘snprintf’ output between 2 and 4097 bytes into a destination of size 4096
  784 |  snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix this simply checking snprintf return code and properly handling the error.

Fixes: e42256699cac ("bpf: make tc's bpf loader generic and move into lib")
Signed-off-by: Andrea Claudi <aclaudi@...hat.com>
---
 lib/bpf.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/bpf.c b/lib/bpf.c
index 23cb0d96a85ba..c7d45077c14e5 100644
--- a/lib/bpf.c
+++ b/lib/bpf.c
@@ -781,7 +781,11 @@ static const char *bpf_get_work_dir(enum bpf_prog_type type)
 		}
 	}
 
-	snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
+	ret = snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
+	if (ret < 0 || ret >= sizeof(bpf_wrk_dir)) {
+		mnt = NULL;
+		goto out;
+	}
 
 	ret = bpf_gen_hierarchy(bpf_wrk_dir);
 	if (ret) {
-- 
2.25.4