Re: [PATCH net-next] net: Silence false field-spanning write warning in metadata_dst memcpy

[Stephen Hemminger <stephen@networkplumber.org>]

On Sun, 18 Aug 2024 14:43:51 +0300
Gal Pressman <gal@nvidia.com> wrote:

> When metadata_dst struct is allocated (using metadata_dst_alloc()), it
> reserves room for options at the end of the struct.
> 
> 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:
> 	------------[ cut here ]------------
> 	memcpy: detected field-spanning write (size 104) of single field "&new_md->u.tun_info" at include/net/dst_metadata.h:166 (size 96)
> 	WARNING: CPU: 2 PID: 391470 at include/net/dst_metadata.h:166 tun_dst_unclone+0x114/0x138 [geneve]
> 	Modules linked in: act_tunnel_key geneve ip6_udp_tunnel udp_tunnel act_vlan act_mirred act_skbedit cls_matchall nfnetlink_cttimeout act_gact cls_flower sch_ingress sbsa_gwdt ipmi_devintf ipmi_msghandler xfrm_interface xfrm6_tunnel tunnel6 tunnel4 xfrm_user xfrm_algo nvme_fabrics overlay optee openvswitch nsh nf_conncount ib_srp scsi_transport_srp rpcrdma rdma_ucm ib_iser rdma_cm ib_umad iw_cm libiscsi ib_ipoib scsi_transport_iscsi ib_cm uio_pdrv_genirq uio mlxbf_pmc pwr_mlxbf mlxbf_bootctl bluefield_edac nft_chain_nat binfmt_misc xt_MASQUERADE nf_nat xt_tcpmss 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 nft_compat nf_tables nfnetlink sch_fq_codel dm_multipath fuse efi_pstore ip_tables btrfs blake2b_generic raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor xor_neon raid6_pq raid1 raid0 nvme nvme_core mlx5_ib ib_uverbs ib_core ipv6 crc_ccitt mlx5_core crct10dif_ce mlxfw
> 	 psample i2c_mlxbf gpio_mlxbf2 mlxbf_gige mlxbf_tmfifo
> 	CPU: 2 PID: 391470 Comm: handler6 Not tainted 6.10.0-rc1 #1
> 	Hardware name: https://www.mellanox.com BlueField SoC/BlueField SoC, BIOS 4.5.0.12993 Dec  6 2023
> 	pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> 	pc : tun_dst_unclone+0x114/0x138 [geneve]
> 	lr : tun_dst_unclone+0x114/0x138 [geneve]
> 	sp : ffffffc0804533f0
> 	x29: ffffffc0804533f0 x28: 000000000000024e x27: 0000000000000000
> 	x26: ffffffdcfc0e8e40 x25: ffffff8086fa6600 x24: ffffff8096a0c000
> 	x23: 0000000000000068 x22: 0000000000000008 x21: ffffff8092ad7000
> 	x20: ffffff8081e17900 x19: ffffff8092ad7900 x18: 00000000fffffffd
> 	x17: 0000000000000000 x16: ffffffdcfa018488 x15: 695f6e75742e753e
> 	x14: 2d646d5f77656e26 x13: 6d5f77656e262220 x12: 646c65696620656c
> 	x11: ffffffdcfbe33ae8 x10: ffffffdcfbe1baa8 x9 : ffffffdcfa0a4c10
> 	x8 : 0000000000017fe8 x7 : c0000000ffffefff x6 : 0000000000000001
> 	x5 : ffffff83fdeeb010 x4 : 0000000000000000 x3 : 0000000000000027
> 	x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffffff80913f6780
> 	Call trace:
> 	 tun_dst_unclone+0x114/0x138 [geneve]
> 	 geneve_xmit+0x214/0x10e0 [geneve]
> 	 dev_hard_start_xmit+0xc0/0x220
> 	 __dev_queue_xmit+0xa14/0xd38
> 	 dev_queue_xmit+0x14/0x28 [openvswitch]
> 	 ovs_vport_send+0x98/0x1c8 [openvswitch]
> 	 do_output+0x80/0x1a0 [openvswitch]
> 	 do_execute_actions+0x172c/0x1958 [openvswitch]
> 	 ovs_execute_actions+0x64/0x1a8 [openvswitch]
> 	 ovs_packet_cmd_execute+0x258/0x2d8 [openvswitch]
> 	 genl_family_rcv_msg_doit+0xc8/0x138
> 	 genl_rcv_msg+0x1ec/0x280
> 	 netlink_rcv_skb+0x64/0x150
> 	 genl_rcv+0x40/0x60
> 	 netlink_unicast+0x2e4/0x348
> 	 netlink_sendmsg+0x1b0/0x400
> 	 __sock_sendmsg+0x64/0xc0
> 	 ____sys_sendmsg+0x284/0x308
> 	 ___sys_sendmsg+0x88/0xf0
> 	 __sys_sendmsg+0x70/0xd8
> 	 __arm64_sys_sendmsg+0x2c/0x40
> 	 invoke_syscall+0x50/0x128
> 	 el0_svc_common.constprop.0+0x48/0xf0
> 	 do_el0_svc+0x24/0x38
> 	 el0_svc+0x38/0x100
> 	 el0t_64_sync_handler+0xc0/0xc8
> 	 el0t_64_sync+0x1a4/0x1a8
> 	---[ end trace 0000000000000000 ]---
> 
> Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
> Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
> Signed-off-by: Gal Pressman <gal@nvidia.com>
> ---
>  include/net/dst_metadata.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/dst_metadata.h b/include/net/dst_metadata.h
> index 4160731dcb6e..84c15402931c 100644
> --- a/include/net/dst_metadata.h
> +++ b/include/net/dst_metadata.h
> @@ -163,8 +163,11 @@ static inline struct metadata_dst *tun_dst_unclone(struct sk_buff *skb)
>  	if (!new_md)
>  		return ERR_PTR(-ENOMEM);
>  
> -	memcpy(&new_md->u.tun_info, &md_dst->u.tun_info,
> -	       sizeof(struct ip_tunnel_info) + md_size);
> +	unsafe_memcpy(&new_md->u.tun_info, &md_dst->u.tun_info,
> +		      sizeof(struct ip_tunnel_info) + md_size,
> +		      /* metadata_dst_alloc() reserves room (md_size bytes) for
> +		       * options right after the ip_tunnel_info struct.
> +		       */);

This is an awkward /* midsentence */ place to put a comment.