linux-kernel - [PATCH AUTOSEL 4.19 162/172] selftests/net: in timestamping, strncpy needs to preserve null byte

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Date:   Wed, 17 Jun 2020 21:22:08 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     tannerlove <tannerlove@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>,
        linux-kselftest@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 162/172] selftests/net: in timestamping, strncpy needs to preserve null byte

From: tannerlove <tannerlove@...gle.com>

[ Upstream commit 8027bc0307ce59759b90679fa5d8b22949586d20 ]

If user passed an interface option longer than 15 characters, then
device.ifr_name and hwtstamp.ifr_name became non-null-terminated
strings. The compiler warned about this:

timestamping.c:353:2: warning: ‘strncpy’ specified bound 16 equals \
destination size [-Wstringop-truncation]
  353 |  strncpy(device.ifr_name, interface, sizeof(device.ifr_name));

Fixes: cb9eff097831 ("net: new user space API for time stamping of incoming and outgoing packets")
Signed-off-by: Tanner Love <tannerlove@...gle.com>
Acked-by: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 .../selftests/networking/timestamping/timestamping.c   | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/networking/timestamping/timestamping.c b/tools/testing/selftests/networking/timestamping/timestamping.c
index 5cdfd743447b..900ed4b47899 100644
--- a/tools/testing/selftests/networking/timestamping/timestamping.c
+++ b/tools/testing/selftests/networking/timestamping/timestamping.c
@@ -332,10 +332,16 @@ int main(int argc, char **argv)
 	int val;
 	socklen_t len;
 	struct timeval next;
+	size_t if_len;
 
 	if (argc < 2)
 		usage(0);
 	interface = argv[1];
+	if_len = strlen(interface);
+	if (if_len >= IFNAMSIZ) {
+		printf("interface name exceeds IFNAMSIZ\n");
+		exit(1);
+	}
 
 	for (i = 2; i < argc; i++) {
 		if (!strcasecmp(argv[i], "SO_TIMESTAMP"))
@@ -369,12 +375,12 @@ int main(int argc, char **argv)
 		bail("socket");
 
 	memset(&device, 0, sizeof(device));
-	strncpy(device.ifr_name, interface, sizeof(device.ifr_name));
+	memcpy(device.ifr_name, interface, if_len + 1);
 	if (ioctl(sock, SIOCGIFADDR, &device) < 0)
 		bail("getting interface IP address");
 
 	memset(&hwtstamp, 0, sizeof(hwtstamp));
-	strncpy(hwtstamp.ifr_name, interface, sizeof(hwtstamp.ifr_name));
+	memcpy(hwtstamp.ifr_name, interface, if_len + 1);
 	hwtstamp.ifr_data = (void *)&hwconfig;
 	memset(&hwconfig, 0, sizeof(hwconfig));
 	hwconfig.tx_type =
-- 
2.25.1