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Subject[PATCH 4.15 072/122] cls_u32: fix use after free in u32_destroy_key()
Date
4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paolo Abeni <pabeni@redhat.com>


[ Upstream commit d7cdee5ea8d28ae1b6922deb0c1badaa3aa0ef8c ]

Li Shuang reported an Oops with cls_u32 due to an use-after-free
in u32_destroy_key(). The use-after-free can be triggered with:

dev=lo
tc qdisc add dev $dev root handle 1: htb default 10
tc filter add dev $dev parent 1: prio 5 handle 1: protocol ip u32 divisor 256
tc filter add dev $dev protocol ip parent 1: prio 5 u32 ht 800:: match ip dst\
10.0.0.0/8 hashkey mask 0x0000ff00 at 16 link 1:
tc qdisc del dev $dev root

Which causes the following kasan splat:

==================================================================
BUG: KASAN: use-after-free in u32_destroy_key.constprop.21+0x117/0x140 [cls_u32]
Read of size 4 at addr ffff881b83dae618 by task kworker/u48:5/571

CPU: 17 PID: 571 Comm: kworker/u48:5 Not tainted 4.15.0+ #87
Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.1.7 06/16/2016
Workqueue: tc_filter_workqueue u32_delete_key_freepf_work [cls_u32]
Call Trace:
dump_stack+0xd6/0x182
? dma_virt_map_sg+0x22e/0x22e
print_address_description+0x73/0x290
kasan_report+0x277/0x360
? u32_destroy_key.constprop.21+0x117/0x140 [cls_u32]
u32_destroy_key.constprop.21+0x117/0x140 [cls_u32]
u32_delete_key_freepf_work+0x1c/0x30 [cls_u32]
process_one_work+0xae0/0x1c80
? sched_clock+0x5/0x10
? pwq_dec_nr_in_flight+0x3c0/0x3c0
? _raw_spin_unlock_irq+0x29/0x40
? trace_hardirqs_on_caller+0x381/0x570
? _raw_spin_unlock_irq+0x29/0x40
? finish_task_switch+0x1e5/0x760
? finish_task_switch+0x208/0x760
? preempt_notifier_dec+0x20/0x20
? __schedule+0x839/0x1ee0
? check_noncircular+0x20/0x20
? firmware_map_remove+0x73/0x73
? find_held_lock+0x39/0x1c0
? worker_thread+0x434/0x1820
? lock_contended+0xee0/0xee0
? lock_release+0x1100/0x1100
? init_rescuer.part.16+0x150/0x150
? retint_kernel+0x10/0x10
worker_thread+0x216/0x1820
? process_one_work+0x1c80/0x1c80
? lock_acquire+0x1a5/0x540
? lock_downgrade+0x6b0/0x6b0
? sched_clock+0x5/0x10
? lock_release+0x1100/0x1100
? compat_start_thread+0x80/0x80
? do_raw_spin_trylock+0x190/0x190
? _raw_spin_unlock_irq+0x29/0x40
? trace_hardirqs_on_caller+0x381/0x570
? _raw_spin_unlock_irq+0x29/0x40
? finish_task_switch+0x1e5/0x760
? finish_task_switch+0x208/0x760
? preempt_notifier_dec+0x20/0x20
? __schedule+0x839/0x1ee0
? kmem_cache_alloc_trace+0x143/0x320
? firmware_map_remove+0x73/0x73
? sched_clock+0x5/0x10
? sched_clock_cpu+0x18/0x170
? find_held_lock+0x39/0x1c0
? schedule+0xf3/0x3b0
? lock_downgrade+0x6b0/0x6b0
? __schedule+0x1ee0/0x1ee0
? do_wait_intr_irq+0x340/0x340
? do_raw_spin_trylock+0x190/0x190
? _raw_spin_unlock_irqrestore+0x32/0x60
? process_one_work+0x1c80/0x1c80
? process_one_work+0x1c80/0x1c80
kthread+0x312/0x3d0
? kthread_create_worker_on_cpu+0xc0/0xc0
ret_from_fork+0x3a/0x50

Allocated by task 1688:
kasan_kmalloc+0xa0/0xd0
__kmalloc+0x162/0x380
u32_change+0x1220/0x3c9e [cls_u32]
tc_ctl_tfilter+0x1ba6/0x2f80
rtnetlink_rcv_msg+0x4f0/0x9d0
netlink_rcv_skb+0x124/0x320
netlink_unicast+0x430/0x600
netlink_sendmsg+0x8fa/0xd60
sock_sendmsg+0xb1/0xe0
___sys_sendmsg+0x678/0x980
__sys_sendmsg+0xc4/0x210
do_syscall_64+0x232/0x7f0
return_from_SYSCALL_64+0x0/0x75

Freed by task 112:
kasan_slab_free+0x71/0xc0
kfree+0x114/0x320
rcu_process_callbacks+0xc3f/0x1600
__do_softirq+0x2bf/0xc06

The buggy address belongs to the object at ffff881b83dae600
which belongs to the cache kmalloc-4096 of size 4096
The buggy address is located 24 bytes inside of
4096-byte region [ffff881b83dae600, ffff881b83daf600)
The buggy address belongs to the page:
page:ffffea006e0f6a00 count:1 mapcount:0 mapping: (null) index:0x0 compound_mapcount: 0
flags: 0x17ffffc0008100(slab|head)
raw: 0017ffffc0008100 0000000000000000 0000000000000000 0000000100070007
raw: dead000000000100 dead000000000200 ffff880187c0e600 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff881b83dae500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff881b83dae580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff881b83dae600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff881b83dae680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff881b83dae700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

The problem is that the htnode is freed before the linked knodes and the
latter will try to access the first at u32_destroy_key() time.
This change addresses the issue using the htnode refcnt to guarantee
the correct free order. While at it also add a RCU annotation,
to keep sparse happy.

v1 -> v2: use rtnl_derefence() instead of RCU read locks
v2 -> v3:
- don't check refcnt in u32_destroy_hnode()
- cleaned-up u32_destroy() implementation
- cleaned-up code comment
v3 -> v4:
- dropped unneeded comment

Reported-by: Li Shuang <shuali@redhat.com>
Fixes: c0d378ef1266 ("net_sched: use tcf_queue_work() in u32 filter")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/cls_u32.c | 21 +++++++++++----------
1 file changed, 11 insertions(+), 10 deletions(-)

--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -397,10 +397,12 @@ static int u32_init(struct tcf_proto *tp
static int u32_destroy_key(struct tcf_proto *tp, struct tc_u_knode *n,
bool free_pf)
{
+ struct tc_u_hnode *ht = rtnl_dereference(n->ht_down);
+
tcf_exts_destroy(&n->exts);
tcf_exts_put_net(&n->exts);
- if (n->ht_down)
- n->ht_down->refcnt--;
+ if (ht && --ht->refcnt == 0)
+ kfree(ht);
#ifdef CONFIG_CLS_U32_PERF
if (free_pf)
free_percpu(n->pf);
@@ -653,16 +655,15 @@ static void u32_destroy(struct tcf_proto

hlist_del(&tp_c->hnode);

- for (ht = rtnl_dereference(tp_c->hlist);
- ht;
- ht = rtnl_dereference(ht->next)) {
- ht->refcnt--;
- u32_clear_hnode(tp, ht);
- }
-
while ((ht = rtnl_dereference(tp_c->hlist)) != NULL) {
+ u32_clear_hnode(tp, ht);
RCU_INIT_POINTER(tp_c->hlist, ht->next);
- kfree_rcu(ht, rcu);
+
+ /* u32_destroy_key() will later free ht for us, if it's
+ * still referenced by some knode
+ */
+ if (--ht->refcnt == 0)
+ kfree_rcu(ht, rcu);
}

idr_destroy(&tp_c->handle_idr);

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