Subject: CVE-2021-47402: net: sched: flower: protect fl_walk() with rcu

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

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] ==================================================================

The Linux kernel CVE team has assigned CVE-2021-47402 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.3 with commit d39d714969cd and fixed in 5.4.151 with commit 694b0cee7f85
	Issue introduced in 5.3 with commit d39d714969cd and fixed in 5.10.71 with commit d0d520c19e7e
	Issue introduced in 5.3 with commit d39d714969cd and fixed in 5.14.10 with commit dab4677bdbff
	Issue introduced in 5.3 with commit d39d714969cd and fixed in 5.15 with commit d5ef190693a7

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47402
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/sched/cls_flower.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/694b0cee7f8546b69a80996a29cb3cf4149c0453
	https://git.kernel.org/stable/c/d0d520c19e7ea19ed38dc5797b12397b6ccf9f88
	https://git.kernel.org/stable/c/dab4677bdbffa5c8270e79e34e51c89efa0728a0
	https://git.kernel.org/stable/c/d5ef190693a7d76c5c192d108e8dec48307b46ee