-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Address the following warnings by changing the type of the middle struct
members in a couple of composite structs, which are currently causing
trouble, from `struct sockaddr` to `struct __kernel_sockaddr_legacy`.

include/uapi/linux/if_arp.h:118:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
include/uapi/linux/if_arp.h:119:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
include/uapi/linux/if_arp.h:121:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
include/uapi/linux/if_arp.h:126:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
include/uapi/linux/if_arp.h:127:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Also, refactor some related code, accordingly.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 include/uapi/linux/if_arp.h | 18 +++++++++---------
 net/ipv4/arp.c              |  2 +-
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/uapi/linux/if_arp.h b/include/uapi/linux/if_arp.h
index 4783af9fe520..4a25a05125d3 100644
--- a/include/uapi/linux/if_arp.h
+++ b/include/uapi/linux/if_arp.h
@@ -115,18 +115,18 @@
 
 /* ARP ioctl request. */
 struct arpreq {
-	struct sockaddr	arp_pa;		/* protocol address		 */
-	struct sockaddr	arp_ha;		/* hardware address		 */
-	int		arp_flags;	/* flags			 */
-	struct sockaddr arp_netmask;    /* netmask (only for proxy arps) */
-	char		arp_dev[IFNAMSIZ];
+	struct __kernel_sockaddr_legacy	arp_pa;		/* protocol address		 */
+	struct __kernel_sockaddr_legacy	arp_ha;		/* hardware address		 */
+	int				arp_flags;	/* flags			 */
+	struct __kernel_sockaddr_legacy	arp_netmask;    /* netmask (only for proxy arps) */
+	char				arp_dev[IFNAMSIZ];
 };
 
 struct arpreq_old {
-	struct sockaddr	arp_pa;		/* protocol address		 */
-	struct sockaddr	arp_ha;		/* hardware address		 */
-	int		arp_flags;	/* flags			 */
-	struct sockaddr	arp_netmask;    /* netmask (only for proxy arps) */
+	struct __kernel_sockaddr_legacy	arp_pa;		/* protocol address		 */
+	struct __kernel_sockaddr_legacy	arp_ha;		/* hardware address		 */
+	int				arp_flags;	/* flags			 */
+	struct sockaddr			arp_netmask;    /* netmask (only for proxy arps) */
 };
 
 /* ARP Flag values. */
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 11c1519b3699..3a97efe1587b 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1185,7 +1185,7 @@ 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);
 
-- 
2.34.1

On Thu, Oct 24, 2024 at 03:13:45PM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Address the following warnings by changing the type of the middle struct
> members in a couple of composite structs, which are currently causing
> trouble, from `struct sockaddr` to `struct __kernel_sockaddr_legacy`.
> 
> include/uapi/linux/if_arp.h:118:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/if_arp.h:119:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/if_arp.h:121:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/if_arp.h:126:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> include/uapi/linux/if_arp.h:127:25: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Also, refactor some related code, accordingly.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook