[PATCH] net/ipv4: Replace tcp_ca_get_name_by_key()'s strncpy() with strscpy()

[Kees Cook <kees@kernel.org>]

Replace the deprecated[1] use of strncpy() in tcp_ca_get_name_by_key().
The only caller passes the results to nla_put_string(), so trailing
padding is not needed.

Since passing "buffer" decays it to a pointer, the size can't be
trivially determined by the compiler. ca->name is the same length,
so strscpy() won't fail (when ca->name is NUL-terminated). Include the
length explicitly instead of using the 2-argument strscpy().

Link: https://github.com/KSPP/linux/issues/90 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Eric Dumazet <edumazet@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: David Ahern <dsahern@kernel.org>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: netdev@vger.kernel.org
---
 net/ipv4/tcp_cong.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 28ffcfbeef14..2a303a7cba59 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -203,9 +203,10 @@ char *tcp_ca_get_name_by_key(u32 key, char *buffer)
 
 	rcu_read_lock();
 	ca = tcp_ca_find_key(key);
-	if (ca)
-		ret = strncpy(buffer, ca->name,
-			      TCP_CA_NAME_MAX);
+	if (ca) {
+		strscpy(buffer, ca->name, TCP_CA_NAME_MAX);
+		ret = buffer;
+	}
 	rcu_read_unlock();
 
 	return ret;
-- 
2.34.1