net: sched: flower: protect fl_walk() with rcu

Patch that refactored fl_walk() to use idr_for_each_entry_continue_ul()
also removed rcu protection of individual filters which causes following
use-after-free when filter is deleted concurrently. Fix fl_walk() to obtain
rcu read lock while iterating and taking the filter reference and temporary
release the lock while calling arg->fn() callback that can sleep.

KASAN trace:

[  352.773640] ==================================================================
[  352.775041] BUG: KASAN: use-after-free in fl_walk+0x159/0x240 [cls_flower]
[  352.776304] Read of size 4 at addr ffff8881c8251480 by task tc/2987

[  352.777862] CPU: 3 PID: 2987 Comm: tc Not tainted 5.15.0-rc2+ #2
[  352.778980] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[  352.781022] Call Trace:
[  352.781573]  dump_stack_lvl+0x46/0x5a
[  352.782332]  print_address_description.constprop.0+0x1f/0x140
[  352.783400]  ? fl_walk+0x159/0x240 [cls_flower]
[  352.784292]  ? fl_walk+0x159/0x240 [cls_flower]
[  352.785138]  kasan_report.cold+0x83/0xdf
[  352.785851]  ? fl_walk+0x159/0x240 [cls_flower]
[  352.786587]  kasan_check_range+0x145/0x1a0
[  352.787337]  fl_walk+0x159/0x240 [cls_flower]
[  352.788163]  ? fl_put+0x10/0x10 [cls_flower]
[  352.789007]  ? __mutex_unlock_slowpath.constprop.0+0x220/0x220
[  352.790102]  tcf_chain_dump+0x231/0x450
[  352.790878]  ? tcf_chain_tp_delete_empty+0x170/0x170
[  352.791833]  ? __might_sleep+0x2e/0xc0
[  352.792594]  ? tfilter_notify+0x170/0x170
[  352.793400]  ? __mutex_unlock_slowpath.constprop.0+0x220/0x220
[  352.794477]  tc_dump_tfilter+0x385/0x4b0
[  352.795262]  ? tc_new_tfilter+0x1180/0x1180
[  352.796103]  ? __mod_node_page_state+0x1f/0xc0
[  352.796974]  ? __build_skb_around+0x10e/0x130
[  352.797826]  netlink_dump+0x2c0/0x560
[  352.798563]  ? netlink_getsockopt+0x430/0x430
[  352.799433]  ? __mutex_unlock_slowpath.constprop.0+0x220/0x220
[  352.800542]  __netlink_dump_start+0x356/0x440
[  352.801397]  rtnetlink_rcv_msg+0x3ff/0x550
[  352.802190]  ? tc_new_tfilter+0x1180/0x1180
[  352.802872]  ? rtnl_calcit.isra.0+0x1f0/0x1f0
[  352.803668]  ? tc_new_tfilter+0x1180/0x1180
[  352.804344]  ? _copy_from_iter_nocache+0x800/0x800
[  352.805202]  ? kasan_set_track+0x1c/0x30
[  352.805900]  netlink_rcv_skb+0xc6/0x1f0
[  352.806587]  ? rht_deferred_worker+0x6b0/0x6b0
[  352.807455]  ? rtnl_calcit.isra.0+0x1f0/0x1f0
[  352.808324]  ? netlink_ack+0x4d0/0x4d0
[  352.809086]  ? netlink_deliver_tap+0x62/0x3d0
[  352.809951]  netlink_unicast+0x353/0x480
[  352.810744]  ? netlink_attachskb+0x430/0x430
[  352.811586]  ? __alloc_skb+0xd7/0x200
[  352.812349]  netlink_sendmsg+0x396/0x680
[  352.813132]  ? netlink_unicast+0x480/0x480
[  352.813952]  ? __import_iovec+0x192/0x210
[  352.814759]  ? netlink_unicast+0x480/0x480
[  352.815580]  sock_sendmsg+0x6c/0x80
[  352.816299]  ____sys_sendmsg+0x3a5/0x3c0
[  352.817096]  ? kernel_sendmsg+0x30/0x30
[  352.817873]  ? __ia32_sys_recvmmsg+0x150/0x150
[  352.818753]  ___sys_sendmsg+0xd8/0x140
[  352.819518]  ? sendmsg_copy_msghdr+0x110/0x110
[  352.820402]  ? ___sys_recvmsg+0xf4/0x1a0
[  352.821110]  ? __copy_msghdr_from_user+0x260/0x260
[  352.821934]  ? _raw_spin_lock+0x81/0xd0
[  352.822680]  ? __handle_mm_fault+0xef3/0x1b20
[  352.823549]  ? rb_insert_color+0x2a/0x270
[  352.824373]  ? copy_page_range+0x16b0/0x16b0
[  352.825209]  ? perf_event_update_userpage+0x2d0/0x2d0
[  352.826190]  ? __fget_light+0xd9/0xf0
[  352.826941]  __sys_sendmsg+0xb3/0x130
[  352.827613]  ? __sys_sendmsg_sock+0x20/0x20
[  352.828377]  ? do_user_addr_fault+0x2c5/0x8a0
[  352.829184]  ? fpregs_assert_state_consistent+0x52/0x60
[  352.830001]  ? exit_to_user_mode_prepare+0x32/0x160
[  352.830845]  do_syscall_64+0x35/0x80
[  352.831445]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[  352.832331] RIP: 0033:0x7f7bee973c17
[  352.833078] Code: 0c 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10
[  352.836202] RSP: 002b:00007ffcbb368e28 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
[  352.837524] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f7bee973c17
[  352.838715] RDX: 0000000000000000 RSI: 00007ffcbb368e50 RDI: 0000000000000003
[  352.839838] RBP: 00007ffcbb36d090 R08: 00000000cea96d79 R09: 00007f7beea34a40
[  352.841021] R10: 00000000004059bb R11: 0000000000000246 R12: 000000000046563f
[  352.842208] R13: 0000000000000000 R14: 0000000000000000 R15: 00007ffcbb36d088

[  352.843784] Allocated by task 2960:
[  352.844451]  kasan_save_stack+0x1b/0x40
[  352.845173]  __kasan_kmalloc+0x7c/0x90
[  352.845873]  fl_change+0x282/0x22db [cls_flower]
[  352.846696]  tc_new_tfilter+0x6cf/0x1180
[  352.847493]  rtnetlink_rcv_msg+0x471/0x550
[  352.848323]  netlink_rcv_skb+0xc6/0x1f0
[  352.849097]  netlink_unicast+0x353/0x480
[  352.849886]  netlink_sendmsg+0x396/0x680
[  352.850678]  sock_sendmsg+0x6c/0x80
[  352.851398]  ____sys_sendmsg+0x3a5/0x3c0
[  352.852202]  ___sys_sendmsg+0xd8/0x140
[  352.852967]  __sys_sendmsg+0xb3/0x130
[  352.853718]  do_syscall_64+0x35/0x80
[  352.854457]  entry_SYSCALL_64_after_hwframe+0x44/0xae

[  352.855830] Freed by task 7:
[  352.856421]  kasan_save_stack+0x1b/0x40
[  352.857139]  kasan_set_track+0x1c/0x30
[  352.857854]  kasan_set_free_info+0x20/0x30
[  352.858609]  __kasan_slab_free+0xed/0x130
[  352.859348]  kfree+0xa7/0x3c0
[  352.859951]  process_one_work+0x44d/0x780
[  352.860685]  worker_thread+0x2e2/0x7e0
[  352.861390]  kthread+0x1f4/0x220
[  352.862022]  ret_from_fork+0x1f/0x30

[  352.862955] Last potentially related work creation:
[  352.863758]  kasan_save_stack+0x1b/0x40
[  352.864378]  kasan_record_aux_stack+0xab/0xc0
[  352.865028]  insert_work+0x30/0x160
[  352.865617]  __queue_work+0x351/0x670
[  352.866261]  rcu_work_rcufn+0x30/0x40
[  352.866917]  rcu_core+0x3b2/0xdb0
[  352.867561]  __do_softirq+0xf6/0x386

[  352.868708] Second to last potentially related work creation:
[  352.869779]  kasan_save_stack+0x1b/0x40
[  352.870560]  kasan_record_aux_stack+0xab/0xc0
[  352.871426]  call_rcu+0x5f/0x5c0
[  352.872108]  queue_rcu_work+0x44/0x50
[  352.872855]  __fl_put+0x17c/0x240 [cls_flower]
[  352.873733]  fl_delete+0xc7/0x100 [cls_flower]
[  352.874607]  tc_del_tfilter+0x510/0xb30
[  352.886085]  rtnetlink_rcv_msg+0x471/0x550
[  352.886875]  netlink_rcv_skb+0xc6/0x1f0
[  352.887636]  netlink_unicast+0x353/0x480
[  352.888285]  netlink_sendmsg+0x396/0x680
[  352.888942]  sock_sendmsg+0x6c/0x80
[  352.889583]  ____sys_sendmsg+0x3a5/0x3c0
[  352.890311]  ___sys_sendmsg+0xd8/0x140
[  352.891019]  __sys_sendmsg+0xb3/0x130
[  352.891716]  do_syscall_64+0x35/0x80
[  352.892395]  entry_SYSCALL_64_after_hwframe+0x44/0xae

[  352.893666] The buggy address belongs to the object at ffff8881c8251000
                which belongs to the cache kmalloc-2k of size 2048
[  352.895696] The buggy address is located 1152 bytes inside of
                2048-byte region [ffff8881c8251000, ffff8881c8251800)
[  352.897640] The buggy address belongs to the page:
[  352.898492] page:00000000213bac35 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1c8250
[  352.900110] head:00000000213bac35 order:3 compound_mapcount:0 compound_pincount:0
[  352.901541] flags: 0x2ffff800010200(slab|head|node=0|zone=2|lastcpupid=0x1ffff)
[  352.902908] raw: 002ffff800010200 0000000000000000 dead000000000122 ffff888100042f00
[  352.904391] raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
[  352.905861] page dumped because: kasan: bad access detected

[  352.907323] Memory state around the buggy address:
[  352.908218]  ffff8881c8251380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  352.909471]  ffff8881c8251400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  352.910735] >ffff8881c8251480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  352.912012]                    ^
[  352.912642]  ffff8881c8251500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  352.913919]  ffff8881c8251580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[  352.915185] ==================================================================

Fixes: d39d7149 ("idr: introduce idr_for_each_entry_continue_ul()")
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Acked-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: David S. Miller <davem@davemloft.net>