CVE-2023-52487: net/mlx5e: Fix peer flow lists handling
In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: Fix peer flow lists handling

The cited change refactored mlx5e_tc_del_fdb_peer_flow() to only clear DUP
flag when list of peer flows has become empty. However, if any concurrent
user holds a reference to a peer flow (for example, the neighbor update
workqueue task is updating peer flow's parent encap entry concurrently),
then the flow will not be removed from the peer list and, consecutively,
DUP flag will remain set. Since mlx5e_tc_del_fdb_peers_flow() calls
mlx5e_tc_del_fdb_peer_flow() for every possible peer index the algorithm
will try to remove the flow from eswitch instances that it has never peered
with causing either NULL pointer dereference when trying to remove the flow
peer list head of peer_index that was never initialized or a warning if the
list debug config is enabled[0].

Fix the issue by always removing the peer flow from the list even when not
releasing the last reference to it.

[0]:

[ 3102.985806] ------------[ cut here ]------------
[ 3102.986223] list_del corruption, ffff888139110698->next is NULL
[ 3102.986757] WARNING: CPU: 2 PID: 22109 at lib/list_debug.c:53 __list_del_entry_valid_or_report+0x4f/0xc0
[ 3102.987561] Modules linked in: act_ct nf_flow_table bonding act_tunnel_key act_mirred act_skbedit vxlan cls_matchall nfnetlink_cttimeout act_gact cls_flower sch_ingress mlx5_vdpa vringh vhost_iotlb vdpa openvswitch nsh xt_MASQUERADE nf_conntrack_netlink nfnetlink iptable_nat xt_addrtype xt_conntrack nf_nat br_netfilter rpcsec_gss_krb5 auth_rpcg
ss oid_registry overlay rpcrdma rdma_ucm ib_iser libiscsi scsi_transport_iscsi ib_umad rdma_cm ib_ipoib iw_cm ib_cm mlx5_ib ib_uverbs ib_core mlx5_core [last unloaded: bonding]
[ 3102.991113] CPU: 2 PID: 22109 Comm: revalidator28 Not tainted 6.6.0-rc6+ #3
[ 3102.991695] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[ 3102.992605] RIP: 0010:__list_del_entry_valid_or_report+0x4f/0xc0
[ 3102.993122] Code: 39 c2 74 56 48 8b 32 48 39 fe 75 62 48 8b 51 08 48 39 f2 75 73 b8 01 00 00 00 c3 48 89 fe 48 c7 c7 48 fd 0a 82 e8 41 0b ad ff <0f> 0b 31 c0 c3 48 89 fe 48 c7 c7 70 fd 0a 82 e8 2d 0b ad ff 0f 0b
[ 3102.994615] RSP: 0018:ffff8881383e7710 EFLAGS: 00010286
[ 3102.995078] RAX: 0000000000000000 RBX: 0000000000000002 RCX: 0000000000000000
[ 3102.995670] RDX: 0000000000000001 RSI: ffff88885f89b640 RDI: ffff88885f89b640
[ 3102.997188] DEL flow 00000000be367878 on port 0
[ 3102.998594] RBP: dead000000000122 R08: 0000000000000000 R09: c0000000ffffdfff
[ 3102.999604] R10: 0000000000000008 R11: ffff8881383e7598 R12: dead000000000100
[ 3103.000198] R13: 0000000000000002 R14: ffff888139110000 R15: ffff888101901240
[ 3103.000790] FS:  00007f424cde4700(0000) GS:ffff88885f880000(0000) knlGS:0000000000000000
[ 3103.001486] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3103.001986] CR2: 00007fd42e8dcb70 CR3: 000000011e68a003 CR4: 0000000000370ea0
[ 3103.002596] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 3103.003190] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 3103.003787] Call Trace:
[ 3103.004055]  <TASK>
[ 3103.004297]  ? __warn+0x7d/0x130
[ 3103.004623]  ? __list_del_entry_valid_or_report+0x4f/0xc0
[ 3103.005094]  ? report_bug+0xf1/0x1c0
[ 3103.005439]  ? console_unlock+0x4a/0xd0
[ 3103.005806]  ? handle_bug+0x3f/0x70
[ 3103.006149]  ? exc_invalid_op+0x13/0x60
[ 3103.006531]  ? asm_exc_invalid_op+0x16/0x20
[ 3103.007430]  ? __list_del_entry_valid_or_report+0x4f/0xc0
[ 3103.007910]  mlx5e_tc_del_fdb_peers_flow+0xcf/0x240 [mlx5_core]
[ 3103.008463]  mlx5e_tc_del_flow+0x46/0x270 [mlx5_core]
[ 3103.008944]  mlx5e_flow_put+0x26/0x50 [mlx5_core]
[ 3103.009401]  mlx5e_delete_flower+0x25f/0x380 [mlx5_core]
[ 3103.009901]  tc_setup_cb_destroy+0xab/0x180
[ 3103.010292]  fl_hw_destroy_filter+0x99/0xc0 [cls_flower]
[ 3103.010779]  __fl_delete+0x2d4/0x2f0 [cls_flower]
[ 3103.0
---truncated---
CVSS v3.1: 5.5