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Date:   Tue, 18 Jul 2023 00:04:19 +0000
Mime-Version: 1.0
Message-ID: <20230718-net-dsa-strncpy-v1-1-e84664747713@google.com>
Subject: [PATCH] net: dsa: remove deprecated strncpy
From:   justinstitt@google.com
To:     Justin Stitt <justinstitt@google.com>,
        Andrew Lunn <andrew@lunn.ch>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Vladimir Oltean <olteanv@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Kees Cook <keescook@chromium.org>,
        Nick Desaulniers <ndesaulniers@google.com>
Content-Type: text/plain; charset="utf-8"
Precedence: bulk

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

Even call sites utilizing length-bounded destination buffers should
switch over to using `strtomem` or `strtomem_pad`. In this case,
however, the compiler is unable to determine the size of the `data`
buffer which renders `strtomem` unusable. Due to this, `strscpy`
should be used.

It should be noted that most call sites already zero-initialize the
destination buffer. However, I've opted to use `strscpy_pad` to maintain
the same exact behavior that `strncpy` produced (zero-padded tail up to
`len`).

Also see [3].

[1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
[2]: elixir.bootlin.com/linux/v6.3/source/net/ethtool/ioctl.c#L1944
[3]: manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html

Link: https://github.com/KSPP/linux/issues/90
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
 net/dsa/slave.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 527b1d576460..c9f77b7e5895 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -1056,10 +1056,10 @@ static void dsa_slave_get_strings(struct net_device *dev,
 	if (stringset == ETH_SS_STATS) {
 		int len = ETH_GSTRING_LEN;
 
-		strncpy(data, "tx_packets", len);
-		strncpy(data + len, "tx_bytes", len);
-		strncpy(data + 2 * len, "rx_packets", len);
-		strncpy(data + 3 * len, "rx_bytes", len);
+		strscpy_pad(data, "tx_packets", len);
+		strscpy_pad(data + len, "tx_bytes", len);
+		strscpy_pad(data + 2 * len, "rx_packets", len);
+		strscpy_pad(data + 3 * len, "rx_bytes", len);
 		if (ds->ops->get_strings)
 			ds->ops->get_strings(ds, dp->index, stringset,
 					     data + 4 * len);

---
base-commit: fdf0eaf11452d72945af31804e2a1048ee1b574c
change-id: 20230717-net-dsa-strncpy-844ca1111eb2

Best regards,
-- 
Justin Stitt <justinstitt@google.com>