netdev - [PATCH net] selftests/net: in timestamping, strncpy needs to preserve null byte

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Message-Id: <20200608193715.122785-1-tannerlove.kernel@gmail.com>
Date:   Mon,  8 Jun 2020 15:37:15 -0400
From:   Tanner Love <tannerlove.kernel@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, tannerlove <tannerlove@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net] selftests/net: in timestamping, strncpy needs to preserve null byte

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

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>
---
 tools/testing/selftests/net/timestamping.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/timestamping.c b/tools/testing/selftests/net/timestamping.c
index aca3491174a1..f4bb4fef0f39 100644
--- a/tools/testing/selftests/net/timestamping.c
+++ b/tools/testing/selftests/net/timestamping.c
@@ -313,10 +313,16 @@ 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"))
@@ -350,12 +356,12 @@ 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 =
-- 
2.27.0.278.ge193c7cf3a9-goog