[PATCH net-next] net: Silence false field-spanning write warning in ip_tunnel_info_opts_set() memcpy

[Gal Pressman <gal@nvidia.com>]

When metadata_dst struct is allocated (using metadata_dst_alloc()), it
reserves room for options at the end of the struct.

Similar to [1], change the memcpy() to unsafe_memcpy() as it is
guaranteed that enough room (md_size bytes) was allocated and the
field-spanning write is intentional.

This resolves the following warning:
  memcpy: detected field-spanning write (size 8) of single field "_Generic(info, const struct ip_tunnel_info * : ((const void *)((info) + 1)), struct ip_tunnel_info * : ((void *)((info) + 1)) )" at include/net/ip_tunnels.h:662 (size 0)
  WARNING: CPU: 0 PID: 19184 at include/net/ip_tunnels.h:662 validate_and_copy_set_tun+0x2f0/0x308 [openvswitch]
  Modules linked in: act_csum act_pedit act_tunnel_key geneve ip6_udp_tunnel udp_tunnel nf_conntrack_netlink act_skbedit act_mirred sbsa_gwdt ipmi_devintf ipmi_msghandler nvme_fabrics nvme_core overlay optee cls_matchall nfnetlink_cttimeout act_gact cls_flower sch_ingress openvswitch nsh nf_conncount nft_chain_nat xt_MASQUERADE nf_nat xt_tcpmss ib_srp scsi_transport_srp xt_NFLOG nfnetlink_log xt_recent xt_hashlimit xt_state xt_conntrack nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 xt_mark xt_comment ipt_REJECT nf_reject_ipv4 rpcrdma nft_compat rdma_ucm ib_umad ib_iser binfmt_misc rdma_cm ib_ipoib iw_cm nf_tables libiscsi scsi_transport_iscsi nfnetlink ib_cm mlx5_ib ib_uverbs ib_core uio_pdrv_genirq uio mlxbf_pmc mlxbf_bootctl bluefield_edac sch_fq_codel dm_multipath fuse efi_pstore ip_tables crct10dif_ce mlx5_core mlxfw psample i2c_mlxbf pwr_mlxbf gpio_mlxbf2 mlxbf_gige mlxbf_tmfifo ipv6 crc_ccitt
  CPU: 0 UID: 0 PID: 19184 Comm: handler2 Not tainted 6.12.0-for-upstream-bluefield-2024-11-29-01-33 #1
  Hardware name: https://www.mellanox.com BlueField SoC/BlueField SoC, BIOS 4.9.0.13378 Oct 30 2024
  pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  pc : validate_and_copy_set_tun+0x2f0/0x308 [openvswitch]
  lr : validate_and_copy_set_tun+0x2f0/0x308 [openvswitch]
  sp : ffffffc0aac6b420
  x29: ffffffc0aac6b420 x28: 0000000000000040 x27: 0000000000000001
  x26: 0000000000000008 x25: 0000000000000001 x24: 0000000000000800
  x23: ffffff8082ab9c00 x22: ffffffc0aac6b480 x21: 0000000000000008
  x20: ffffffc0aac6b830 x19: 0000000000000000 x18: ffffffffffffffff
  x17: 1514131211100000 x16: ffffffea66bab8d8 x15: 2b20296f666e6928
  x14: 28292a2064696f76 x13: 6c636e6920746120 x12: ffffffea68a6e5d0
  x11: 0000000000000001 x10: 0000000000000001 x9 : ffffffea66c399b8
  x8 : c0000000ffffefff x7 : ffffffea68a163e0 x6 : 0000000000000001
  x5 : ffffff83fdeae488 x4 : 0000000000000000 x3 : 0000000000000027
  x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffffff80979f2280
  Call trace:
   validate_and_copy_set_tun+0x2f0/0x308 [openvswitch] (P)
   validate_and_copy_set_tun+0x2f0/0x308 [openvswitch] (L)
   validate_set.constprop.0+0x2dc/0x438 [openvswitch]
   __ovs_nla_copy_actions+0x404/0xd48 [openvswitch]
   ovs_nla_copy_actions+0xb4/0x160 [openvswitch]
   ovs_packet_cmd_execute+0x1bc/0x2f0 [openvswitch]
   genl_family_rcv_msg_doit+0xd0/0x140
   genl_rcv_msg+0x1f0/0x280
   netlink_rcv_skb+0x64/0x138
   genl_rcv+0x40/0x60
   netlink_unicast+0x2e8/0x348
   netlink_sendmsg+0x1ac/0x400
   __sock_sendmsg+0x64/0xc0
   ____sys_sendmsg+0x26c/0x2f0
   ___sys_sendmsg+0x88/0xf0
   __sys_sendmsg+0x88/0x100
   __arm64_sys_sendmsg+0x2c/0x40
   invoke_syscall+0x50/0x120
   el0_svc_common.constprop.0+0x48/0xf0
   do_el0_svc+0x24/0x38
   el0_svc+0x34/0xf0
   el0t_64_sync_handler+0x10c/0x138
   el0t_64_sync+0x1ac/0x1b0

[1] Commit 13cfd6a6d7ac ("net: Silence false field-spanning write warning in metadata_dst memcpy")

Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Signed-off-by: Gal Pressman <gal@nvidia.com>
---
 include/net/ip_tunnels.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
index 1aa31bdb2b31..d5e163eba234 100644
--- a/include/net/ip_tunnels.h
+++ b/include/net/ip_tunnels.h
@@ -659,7 +659,10 @@ static inline void ip_tunnel_info_opts_set(struct ip_tunnel_info *info,
 {
 	info->options_len = len;
 	if (len > 0) {
-		memcpy(ip_tunnel_info_opts(info), from, len);
+		unsafe_memcpy(ip_tunnel_info_opts(info), from, len,
+			      /* metadata_dst_alloc() reserves room (md_size bytes)
+			       * for options right after the ip_tunnel_info struct.
+			       */);
 		ip_tunnel_flags_or(info->key.tun_flags, info->key.tun_flags,
 				   flags);
 	}
-- 
2.40.1