On Fri, 2018-02-02 at 15:30 +0100, Paolo Abeni wrote:
> 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
>
> Reported-by: Li Shuang <shu...@redhat.com>
> Fixes: c0d378ef1266 ("net_sched: use tcf_queue_work() in u32 filter")
> Signed-off-by: Paolo Abeni <pab...@redhat.com>
> ---
> net/sched/cls_u32.c | 19 +++++++++++++++----
> 1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> index 60c892c36a60..10440fbf3c68 100644
> --- a/net/sched/cls_u32.c
> +++ b/net/sched/cls_u32.c
> @@ -398,10 +398,12 @@ 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)
oops... this ^^^^^^^^^^^^ should be: '--th->refcnt' ...
>
> + kfree(ht);
#ifdef CONFIG_CLS_U32_PERF
> if (free_pf)
> free_percpu(n->pf);
> @@ -624,7 +626,12 @@ static int u32_destroy_hnode(struct tcf_proto *tp,
> struct tc_u_hnode *ht,
> idr_destroy(&ht->handle_idr);
> idr_remove_ext(&tp_c->handle_idr, ht->handle);
> RCU_INIT_POINTER(*hn, ht->next);
> - kfree_rcu(ht, rcu);
> +
> + /* u32_destroy_key() will will later free ht for us, if
> + * it's still referenced by some knode
> + */
> + if (ht->refcnt == 0)
> + kfree_rcu(ht, rcu);
> return 0;
> }
> }
> @@ -667,7 +674,11 @@ static void u32_destroy(struct tcf_proto *tp, struct
> netlink_ext_ack *extack)
>
> while ((ht = rtnl_dereference(tp_c->hlist)) != NULL) {
> RCU_INIT_POINTER(tp_c->hlist, ht->next);
> - kfree_rcu(ht, rcu);
> + /* u32_destroy_key() will will later free ht for us, if
> + * it's still referenced by some knode
> + */
> + if (ht->refcnt == 0)
> + kfree_rcu(ht, rcu);
And it's probably better merge the previous loop with this one.
I'll include the above changes in v3
Paolo
