Subject: [PATCH v2 10/10] net: Convert struct sockaddr to fixed-size "sa_data[14]"

From: Kees Cook <[email-masked]>
Date: Tue, 14 Oct 2025 15:43:32 -0700

Revert struct sockaddr from flexible array to fixed 14-byte "sa_data",
solves over 36,000 -Wflex-array-member-not-at-end warnings, since struct
sockaddr is embedded within many network structs.

With socket/proto sockaddr-based internal APIs switched to use struct
sockaddr_unspec, there should be no more uses of struct sockaddr that
depend on reading beyond the end of struct sockaddr::sa_data that might
trigger bounds checking.

Comparing an x86_64 "allyesconfig" vmlinux build before and after this
patch showed no new "ud1" instructions from CONFIG_UBSAN_BOUNDS nor any
explicit "field-spanning" memcpy CONFIG_FORTIFY_SOURCE instrumentations.

Cc: "Gustavo A. R. Silva" <[email-masked]>
Signed-off-by: Kees Cook <[email-masked]>
---
 include/linux/socket.h                         |  6 ++----
 tools/perf/trace/beauty/include/linux/socket.h |  5 +----
 net/core/dev.c                                 |  2 +-
 net/core/dev_ioctl.c                           |  2 +-
 net/ipv4/arp.c                                 |  2 +-
 net/packet/af_packet.c                         | 10 +++++-----
 6 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 27f57c7ee02a..5e9d83cec850 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -32,12 +32,10 @@ typedef __kernel_sa_family_t	sa_family_t;
  *	1003.1g requires sa_family_t and that sa_data is char.
  */
 
+/* Deprecated for in-kernel use. Use struct sockaddr_unspec instead. */
 struct sockaddr {
 	sa_family_t	sa_family;	/* address family, AF_xxx	*/
-	union {
-		char sa_data_min[14];		/* Minimum 14 bytes of protocol address	*/
-		DECLARE_FLEX_ARRAY(char, sa_data);
-	};
+	char		sa_data[14];	/* 14 bytes of protocol address	*/
 };
 
 /**
diff --git a/tools/perf/trace/beauty/include/linux/socket.h b/tools/perf/trace/beauty/include/linux/socket.h
index 3b262487ec06..77d7c59f5d8b 100644
--- a/tools/perf/trace/beauty/include/linux/socket.h
+++ b/tools/perf/trace/beauty/include/linux/socket.h
@@ -34,10 +34,7 @@ typedef __kernel_sa_family_t	sa_family_t;
 
 struct sockaddr {
 	sa_family_t	sa_family;	/* address family, AF_xxx	*/
-	union {
-		char sa_data_min[14];		/* Minimum 14 bytes of protocol address	*/
-		DECLARE_FLEX_ARRAY(char, sa_data);
-	};
+	char		sa_data[14];	/* 14 bytes of protocol address	*/
 };
 
 struct linger {
diff --git a/net/core/dev.c b/net/core/dev.c
index a64cef2c537e..6dc5861f87b0 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9885,7 +9885,7 @@ DECLARE_RWSEM(dev_addr_sem);
 /* "sa" is a true struct sockaddr with limited "sa_data" member. */
 int netif_get_mac_address(struct sockaddr *sa, struct net *net, char *dev_name)
 {
-	size_t size = sizeof(sa->sa_data_min);
+	size_t size = sizeof(sa->sa_data);
 	struct net_device *dev;
 	int ret = 0;
 
diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
index ad54b12d4b4c..b3ce0fb24a69 100644
--- a/net/core/dev_ioctl.c
+++ b/net/core/dev_ioctl.c
@@ -596,7 +596,7 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, void __user *data,
 		if (ifr->ifr_hwaddr.sa_family != dev->type)
 			return -EINVAL;
 		memcpy(dev->broadcast, ifr->ifr_hwaddr.sa_data,
-		       min(sizeof(ifr->ifr_hwaddr.sa_data_min),
+		       min(sizeof(ifr->ifr_hwaddr.sa_data),
 			   (size_t)dev->addr_len));
 		netdev_lock_ops(dev);
 		call_netdevice_notifiers(NETDEV_CHANGEADDR, dev);
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 833f2cf97178..8316ca59088a 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1189,7 +1189,7 @@ static int arp_req_get(struct net *net, struct arpreq *r)
 
 	read_lock_bh(&neigh->lock);
 	memcpy(r->arp_ha.sa_data, neigh->ha,
-	       min(dev->addr_len, sizeof(r->arp_ha.sa_data_min)));
+	       min(dev->addr_len, sizeof(r->arp_ha.sa_data)));
 	r->arp_flags = arp_state_to_flags(neigh);
 	read_unlock_bh(&neigh->lock);
 
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 73bea76ea45d..d21483cae94f 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3284,7 +3284,7 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr_unspec *uaddr,
 {
 	struct sock *sk = sock->sk;
 	struct sockaddr *sa = (struct sockaddr *)uaddr;
-	char name[sizeof(sa->sa_data_min) + 1];
+	char name[sizeof(sa->sa_data) + 1];
 
 	/*
 	 *	Check legality
@@ -3295,8 +3295,8 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr_unspec *uaddr,
 	/* uaddr->sa_data comes from the userspace, it's not guaranteed to be
 	 * zero-terminated.
 	 */
-	memcpy(name, sa->sa_data, sizeof(sa->sa_data_min));
-	name[sizeof(sa->sa_data_min)] = 0;
+	memcpy(name, sa->sa_data, sizeof(sa->sa_data));
+	name[sizeof(sa->sa_data)] = 0;
 
 	return packet_do_bind(sk, name, 0, 0);
 }
@@ -3581,11 +3581,11 @@ static int packet_getname_spkt(struct socket *sock, struct sockaddr *uaddr,
 		return -EOPNOTSUPP;
 
 	uaddr->sa_family = AF_PACKET;
-	memset(uaddr->sa_data, 0, sizeof(uaddr->sa_data_min));
+	memset(uaddr->sa_data, 0, sizeof(uaddr->sa_data));
 	rcu_read_lock();
 	dev = dev_get_by_index_rcu(sock_net(sk), READ_ONCE(pkt_sk(sk)->ifindex));
 	if (dev)
-		strscpy(uaddr->sa_data, dev->name, sizeof(uaddr->sa_data_min));
+		strscpy(uaddr->sa_data, dev->name, sizeof(uaddr->sa_data));
 	rcu_read_unlock();
 
 	return sizeof(*uaddr);
-- 
2.34.1