During reload (or module unload), the router block is de-initialized.
Among other things, this results in the removal of a default multicast
route from each active virtual router (VRF). These default routes are
configured during initialization to trap packets to the CPU. In
Spectrum-2, unlike Spectrum-1, multicast routes are implemented using
ACL rules.

Since the router block is de-initialized before the ACL block, it is
possible that the ACL rules corresponding to the default routes are
deleted while being accessed by the ACL delayed work that queries rules'
activity from the device. This can result in a rare use-after-free [1].

Fix this by protecting the rules list accessed by the delayed work with
a lock. We cannot use a spinlock as the activity read operation is
blocking.

[1]
[  123.331662] ==================================================================
[  123.339920] BUG: KASAN: use-after-free in mlxsw_sp_acl_rule_activity_update_work+0x330/0x3b0
[  123.349381] Read of size 8 at addr ffff8881f3bb4520 by task kworker/0:2/78
[  123.357080]
[  123.358773] CPU: 0 PID: 78 Comm: kworker/0:2 Not tainted 5.5.0-rc5-custom-33108-gf5df95d3ef41 #2209
[  123.368898] Hardware name: Mellanox Technologies Ltd. MSN3700C/VMOD0008, BIOS 5.11 10/10/2018
[  123.378456] Workqueue: mlxsw_core mlxsw_sp_acl_rule_activity_update_work
[  123.385970] Call Trace:
[  123.388734]  dump_stack+0xc6/0x11e
[  123.392568]  print_address_description.constprop.4+0x21/0x340
[  123.403236]  __kasan_report.cold.8+0x76/0xb1
[  123.414884]  kasan_report+0xe/0x20
[  123.418716]  mlxsw_sp_acl_rule_activity_update_work+0x330/0x3b0
[  123.444034]  process_one_work+0xb06/0x19a0
[  123.453731]  worker_thread+0x91/0xe90
[  123.467348]  kthread+0x348/0x410
[  123.476847]  ret_from_fork+0x24/0x30
[  123.480863]
[  123.482545] Allocated by task 73:
[  123.486273]  save_stack+0x19/0x80
[  123.490000]  __kasan_kmalloc.constprop.6+0xc1/0xd0
[  123.495379]  mlxsw_sp_acl_rule_create+0xa7/0x230
[  123.500566]  mlxsw_sp2_mr_tcam_route_create+0xf6/0x3e0
[  123.506334]  mlxsw_sp_mr_tcam_route_create+0x5b4/0x820
[  123.512102]  mlxsw_sp_mr_table_create+0x3b5/0x690
[  123.517389]  mlxsw_sp_vr_get+0x289/0x4d0
[  123.521797]  mlxsw_sp_fib_node_get+0xa2/0x990
[  123.526692]  mlxsw_sp_router_fib4_event_work+0x54c/0x2d60
[  123.532752]  process_one_work+0xb06/0x19a0
[  123.537352]  worker_thread+0x91/0xe90
[  123.541471]  kthread+0x348/0x410
[  123.545103]  ret_from_fork+0x24/0x30
[  123.549113]
[  123.550795] Freed by task 518:
[  123.554231]  save_stack+0x19/0x80
[  123.557958]  __kasan_slab_free+0x125/0x170
[  123.562556]  kfree+0xd7/0x3a0
[  123.565895]  mlxsw_sp_acl_rule_destroy+0x63/0xd0
[  123.571081]  mlxsw_sp2_mr_tcam_route_destroy+0xd5/0x130
[  123.576946]  mlxsw_sp_mr_tcam_route_destroy+0xba/0x260
[  123.582714]  mlxsw_sp_mr_table_destroy+0x1ab/0x290
[  123.588091]  mlxsw_sp_vr_put+0x1db/0x350
[  123.592496]  mlxsw_sp_fib_node_put+0x298/0x4c0
[  123.597486]  mlxsw_sp_vr_fib_flush+0x15b/0x360
[  123.602476]  mlxsw_sp_router_fib_flush+0xba/0x470
[  123.607756]  mlxsw_sp_vrs_fini+0xaa/0x120
[  123.612260]  mlxsw_sp_router_fini+0x137/0x384
[  123.617152]  mlxsw_sp_fini+0x30a/0x4a0
[  123.621374]  mlxsw_core_bus_device_unregister+0x159/0x600
[  123.627435]  mlxsw_devlink_core_bus_device_reload_down+0x7e/0xb0
[  123.634176]  devlink_reload+0xb4/0x380
[  123.638391]  devlink_nl_cmd_reload+0x610/0x700
[  123.643382]  genl_rcv_msg+0x6a8/0xdc0
[  123.647497]  netlink_rcv_skb+0x134/0x3a0
[  123.651904]  genl_rcv+0x29/0x40
[  123.655436]  netlink_unicast+0x4d4/0x700
[  123.659843]  netlink_sendmsg+0x7c0/0xc70
[  123.664251]  __sys_sendto+0x265/0x3c0
[  123.668367]  __x64_sys_sendto+0xe2/0x1b0
[  123.672773]  do_syscall_64+0xa0/0x530
[  123.676892]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[  123.682552]
[  123.684238] The buggy address belongs to the object at ffff8881f3bb4500
[  123.684238]  which belongs to the cache kmalloc-128 of size 128
[  123.698261] The buggy address is located 32 bytes inside of
[  123.698261]  128-byte region [ffff8881f3bb4500, ffff8881f3bb4580)
[  123.711303] The buggy address belongs to the page:
[  123.716682] page:ffffea0007ceed00 refcount:1 mapcount:0 mapping:ffff888236403500 index:0x0
[  123.725958] raw: 0200000000000200 dead000000000100 dead000000000122 ffff888236403500
[  123.734646] raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
[  123.743315] page dumped because: kasan: bad access detected
[  123.749562]
[  123.751241] Memory state around the buggy address:
[  123.756620]  ffff8881f3bb4400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[  123.764716]  ffff8881f3bb4480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[  123.772812] >ffff8881f3bb4500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  123.780904]                                ^
[  123.785697]  ffff8881f3bb4580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[  123.793793]  ffff8881f3bb4600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[  123.801883] ==================================================================

Fixes: cf7221a4 ("mlxsw: spectrum_router: Add Multicast routing support for Spectrum-2")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>