Subject: Re: net: deadlock between ip_expire/sch_direct_xmit

From: Paolo Abeni <[email-masked]>
Date: Tue, 14 Mar 2017 16:03:05 +0100

On Tue, 2017-03-14 at 07:41 -0700, Eric Dumazet wrote:
> On Tue, 2017-03-14 at 14:31 +0100, Dmitry Vyukov wrote:
> > Hello,
> > 
> > I've got the following deadlock report while running syzkaller fuzzer
> > on net-next/92cd12c5ed432c5eebd2462d666772a8d8442c3b:
> > 
> > 
> > [ INFO: possible circular locking dependency detected ]
> > 4.10.0+ #29 Not tainted
> > -------------------------------------------------------
> > modprobe/12392 is trying to acquire lock:
> >  (_xmit_ETHER#2){+.-...}, at: [<ffffffff837a8182>] spin_lock
> > include/linux/spinlock.h:299 [inline]
> >  (_xmit_ETHER#2){+.-...}, at: [<ffffffff837a8182>] __netif_tx_lock
> > include/linux/netdevice.h:3486 [inline]
> >  (_xmit_ETHER#2){+.-...}, at: [<ffffffff837a8182>]
> > sch_direct_xmit+0x282/0x6d0 net/sched/sch_generic.c:180
> > 
> > but task is already holding lock:
> >  (&(&q->lock)->rlock){+.-...}, at: [<ffffffff8389a4d1>] spin_lock
> > include/linux/spinlock.h:299 [inline]
> >  (&(&q->lock)->rlock){+.-...}, at: [<ffffffff8389a4d1>]
> > ip_expire+0x51/0x6c0 net/ipv4/ip_fragment.c:201
> > 
> > which lock already depends on the new lock.
> > 
> > 
> > the existing dependency chain (in reverse order) is:
> > 
> > -> #1 (&(&q->lock)->rlock){+.-...}:
> >        validate_chain kernel/locking/lockdep.c:2267 [inline]
> >        __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> >        lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> >        __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> >        _raw_spin_lock+0x33/0x50 kernel/locking/spinlock.c:151
> >        spin_lock include/linux/spinlock.h:299 [inline]
> >        ip_defrag+0x3a2/0x4130 net/ipv4/ip_fragment.c:669
> >        ip_check_defrag+0x4e3/0x8b0 net/ipv4/ip_fragment.c:713
> >        packet_rcv_fanout+0x282/0x800 net/packet/af_packet.c:1459
> >        deliver_skb net/core/dev.c:1834 [inline]
> >        dev_queue_xmit_nit+0x294/0xa90 net/core/dev.c:1890
> >        xmit_one net/core/dev.c:2903 [inline]
> >        dev_hard_start_xmit+0x16b/0xab0 net/core/dev.c:2923
> >        sch_direct_xmit+0x31f/0x6d0 net/sched/sch_generic.c:182
> >        __dev_xmit_skb net/core/dev.c:3092 [inline]
> >        __dev_queue_xmit+0x13e5/0x1e60 net/core/dev.c:3358
> >        dev_queue_xmit+0x17/0x20 net/core/dev.c:3423
> >        neigh_resolve_output+0x6b9/0xb10 net/core/neighbour.c:1308
> >        neigh_output include/net/neighbour.h:478 [inline]
> >        ip_finish_output2+0x8b8/0x15a0 net/ipv4/ip_output.c:228
> >        ip_do_fragment+0x1d93/0x2720 net/ipv4/ip_output.c:672
> >        ip_fragment.constprop.54+0x145/0x200 net/ipv4/ip_output.c:545
> >        ip_finish_output+0x82d/0xe10 net/ipv4/ip_output.c:314
> >        NF_HOOK_COND include/linux/netfilter.h:246 [inline]
> >        ip_output+0x1f0/0x7a0 net/ipv4/ip_output.c:404
> >        dst_output include/net/dst.h:486 [inline]
> >        ip_local_out+0x95/0x170 net/ipv4/ip_output.c:124
> >        ip_send_skb+0x3c/0xc0 net/ipv4/ip_output.c:1492
> >        ip_push_pending_frames+0x64/0x80 net/ipv4/ip_output.c:1512
> >        raw_sendmsg+0x26de/0x3a00 net/ipv4/raw.c:655
> >        inet_sendmsg+0x164/0x5b0 net/ipv4/af_inet.c:761
> >        sock_sendmsg_nosec net/socket.c:633 [inline]
> >        sock_sendmsg+0xca/0x110 net/socket.c:643
> >        ___sys_sendmsg+0x4a3/0x9f0 net/socket.c:1985
> >        __sys_sendmmsg+0x25c/0x750 net/socket.c:2075
> >        SYSC_sendmmsg net/socket.c:2106 [inline]
> >        SyS_sendmmsg+0x35/0x60 net/socket.c:2101
> >        do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:281
> >        return_from_SYSCALL_64+0x0/0x7a
> > 
> > -> #0 (_xmit_ETHER#2){+.-...}:
> >        check_prev_add kernel/locking/lockdep.c:1830 [inline]
> >        check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1940
> >        validate_chain kernel/locking/lockdep.c:2267 [inline]
> >        __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> >        lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> >        __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> >        _raw_spin_lock+0x33/0x50 kernel/locking/spinlock.c:151
> >        spin_lock include/linux/spinlock.h:299 [inline]
> >        __netif_tx_lock include/linux/netdevice.h:3486 [inline]
> >        sch_direct_xmit+0x282/0x6d0 net/sched/sch_generic.c:180
> >        __dev_xmit_skb net/core/dev.c:3092 [inline]
> >        __dev_queue_xmit+0x13e5/0x1e60 net/core/dev.c:3358
> >        dev_queue_xmit+0x17/0x20 net/core/dev.c:3423
> >        neigh_hh_output include/net/neighbour.h:468 [inline]
> >        neigh_output include/net/neighbour.h:476 [inline]
> >        ip_finish_output2+0xf6c/0x15a0 net/ipv4/ip_output.c:228
> >        ip_finish_output+0xa29/0xe10 net/ipv4/ip_output.c:316
> >        NF_HOOK_COND include/linux/netfilter.h:246 [inline]
> >        ip_output+0x1f0/0x7a0 net/ipv4/ip_output.c:404
> >        dst_output include/net/dst.h:486 [inline]
> >        ip_local_out+0x95/0x170 net/ipv4/ip_output.c:124
> >        ip_send_skb+0x3c/0xc0 net/ipv4/ip_output.c:1492
> >        ip_push_pending_frames+0x64/0x80 net/ipv4/ip_output.c:1512
> >        icmp_push_reply+0x372/0x4d0 net/ipv4/icmp.c:394
> >        icmp_send+0x156c/0x1c80 net/ipv4/icmp.c:754
> >        ip_expire+0x40e/0x6c0 net/ipv4/ip_fragment.c:239
> >        call_timer_fn+0x241/0x820 kernel/time/timer.c:1268
> >        expire_timers kernel/time/timer.c:1307 [inline]
> >        __run_timers+0x960/0xcf0 kernel/time/timer.c:1601
> >        run_timer_softirq+0x21/0x80 kernel/time/timer.c:1614
> >        __do_softirq+0x31f/0xbe7 kernel/softirq.c:284
> >        invoke_softirq kernel/softirq.c:364 [inline]
> >        irq_exit+0x1cc/0x200 kernel/softirq.c:405
> >        exiting_irq arch/x86/include/asm/apic.h:657 [inline]
> >        smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:962
> >        apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:707
> >        __read_once_size include/linux/compiler.h:254 [inline]
> >        atomic_read arch/x86/include/asm/atomic.h:26 [inline]
> >        rcu_dynticks_curr_cpu_in_eqs kernel/rcu/tree.c:350 [inline]
> >        __rcu_is_watching kernel/rcu/tree.c:1133 [inline]
> >        rcu_is_watching+0x83/0x110 kernel/rcu/tree.c:1147
> >        rcu_read_lock_held+0x87/0xc0 kernel/rcu/update.c:293
> >        radix_tree_deref_slot include/linux/radix-tree.h:238 [inline]
> >        filemap_map_pages+0x6d4/0x1570 mm/filemap.c:2335
> >        do_fault_around mm/memory.c:3231 [inline]
> >        do_read_fault mm/memory.c:3265 [inline]
> >        do_fault+0xbd5/0x2080 mm/memory.c:3370
> >        handle_pte_fault mm/memory.c:3600 [inline]
> >        __handle_mm_fault+0x1062/0x2cb0 mm/memory.c:3714
> >        handle_mm_fault+0x1e2/0x480 mm/memory.c:3751
> >        __do_page_fault+0x4f6/0xb60 arch/x86/mm/fault.c:1397
> >        do_page_fault+0x54/0x70 arch/x86/mm/fault.c:1460
> >        page_fault+0x28/0x30 arch/x86/entry/entry_64.S:1011
> > 
> > other info that might help us debug this:
> > 
> >  Possible unsafe locking scenario:
> > 
> >        CPU0                    CPU1
> >        ----                    ----
> >   lock(&(&q->lock)->rlock);
> >                                lock(_xmit_ETHER#2);
> >                                lock(&(&q->lock)->rlock);
> >   lock(_xmit_ETHER#2);
> > 
> >  *** DEADLOCK ***
> > 
> > 10 locks held by modprobe/12392:
> >  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff81329758>]
> > __do_page_fault+0x2b8/0xb60 arch/x86/mm/fault.c:1336
> >  #1:  (rcu_read_lock){......}, at: [<ffffffff8188cab6>]
> > filemap_map_pages+0x1e6/0x1570 mm/filemap.c:2324
> >  #2:  (&(ptlock_ptr(page))->rlock#2){+.+...}, at: [<ffffffff81984a78>]
> > spin_lock include/linux/spinlock.h:299 [inline]
> >  #2:  (&(ptlock_ptr(page))->rlock#2){+.+...}, at: [<ffffffff81984a78>]
> > pte_alloc_one_map mm/memory.c:2944 [inline]
> >  #2:  (&(ptlock_ptr(page))->rlock#2){+.+...}, at: [<ffffffff81984a78>]
> > alloc_set_pte+0x13b8/0x1b90 mm/memory.c:3072
> >  #3:  (((&q->timer))){+.-...}, at: [<ffffffff81627e72>]
> > lockdep_copy_map include/linux/lockdep.h:175 [inline]
> >  #3:  (((&q->timer))){+.-...}, at: [<ffffffff81627e72>]
> > call_timer_fn+0x1c2/0x820 kernel/time/timer.c:1258
> >  #4:  (&(&q->lock)->rlock){+.-...}, at: [<ffffffff8389a4d1>] spin_lock
> > include/linux/spinlock.h:299 [inline]
> >  #4:  (&(&q->lock)->rlock){+.-...}, at: [<ffffffff8389a4d1>]
> > ip_expire+0x51/0x6c0 net/ipv4/ip_fragment.c:201
> >  #5:  (rcu_read_lock){......}, at: [<ffffffff8389a633>]
> > ip_expire+0x1b3/0x6c0 net/ipv4/ip_fragment.c:216
> >  #6:  (slock-AF_INET){+.-...}, at: [<ffffffff839b3313>] spin_trylock
> > include/linux/spinlock.h:309 [inline]
> >  #6:  (slock-AF_INET){+.-...}, at: [<ffffffff839b3313>] icmp_xmit_lock
> > net/ipv4/icmp.c:219 [inline]
> >  #6:  (slock-AF_INET){+.-...}, at: [<ffffffff839b3313>]
> > icmp_send+0x803/0x1c80 net/ipv4/icmp.c:681
> >  #7:  (rcu_read_lock_bh){......}, at: [<ffffffff838ab9a1>]
> > ip_finish_output2+0x2c1/0x15a0 net/ipv4/ip_output.c:198
> >  #8:  (rcu_read_lock_bh){......}, at: [<ffffffff836d1dee>]
> > __dev_queue_xmit+0x23e/0x1e60 net/core/dev.c:3324
> >  #9:  (dev->qdisc_running_key ?: &qdisc_running_key){+.....}, at:
> > [<ffffffff836d3a27>] dev_queue_xmit+0x17/0x20 net/core/dev.c:3423
> > 
> > stack backtrace:
> > CPU: 0 PID: 12392 Comm: modprobe Not tainted 4.10.0+ #29
> > Hardware name: Google Google Compute Engine/Google Compute Engine,
> > BIOS Google 01/01/2011
> > Call Trace:
> >  <IRQ>
> >  __dump_stack lib/dump_stack.c:16 [inline]
> >  dump_stack+0x2ee/0x3ef lib/dump_stack.c:52
> >  print_circular_bug+0x307/0x3b0 kernel/locking/lockdep.c:1204
> >  check_prev_add kernel/locking/lockdep.c:1830 [inline]
> >  check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1940
> >  validate_chain kernel/locking/lockdep.c:2267 [inline]
> >  __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> >  lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> >  __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> >  _raw_spin_lock+0x33/0x50 kernel/locking/spinlock.c:151
> >  spin_lock include/linux/spinlock.h:299 [inline]
> >  __netif_tx_lock include/linux/netdevice.h:3486 [inline]
> >  sch_direct_xmit+0x282/0x6d0 net/sched/sch_generic.c:180
> >  __dev_xmit_skb net/core/dev.c:3092 [inline]
> >  __dev_queue_xmit+0x13e5/0x1e60 net/core/dev.c:3358
> >  dev_queue_xmit+0x17/0x20 net/core/dev.c:3423
> >  neigh_hh_output include/net/neighbour.h:468 [inline]
> >  neigh_output include/net/neighbour.h:476 [inline]
> >  ip_finish_output2+0xf6c/0x15a0 net/ipv4/ip_output.c:228
> >  ip_finish_output+0xa29/0xe10 net/ipv4/ip_output.c:316
> >  NF_HOOK_COND include/linux/netfilter.h:246 [inline]
> >  ip_output+0x1f0/0x7a0 net/ipv4/ip_output.c:404
> >  dst_output include/net/dst.h:486 [inline]
> >  ip_local_out+0x95/0x170 net/ipv4/ip_output.c:124
> >  ip_send_skb+0x3c/0xc0 net/ipv4/ip_output.c:1492
> >  ip_push_pending_frames+0x64/0x80 net/ipv4/ip_output.c:1512
> >  icmp_push_reply+0x372/0x4d0 net/ipv4/icmp.c:394
> >  icmp_send+0x156c/0x1c80 net/ipv4/icmp.c:754
> >  ip_expire+0x40e/0x6c0 net/ipv4/ip_fragment.c:239
> >  call_timer_fn+0x241/0x820 kernel/time/timer.c:1268
> >  expire_timers kernel/time/timer.c:1307 [inline]
> >  __run_timers+0x960/0xcf0 kernel/time/timer.c:1601
> >  run_timer_softirq+0x21/0x80 kernel/time/timer.c:1614
> >  __do_softirq+0x31f/0xbe7 kernel/softirq.c:284
> >  invoke_softirq kernel/softirq.c:364 [inline]
> >  irq_exit+0x1cc/0x200 kernel/softirq.c:405
> >  exiting_irq arch/x86/include/asm/apic.h:657 [inline]
> >  smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:962
> >  apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:707
> > RIP: 0010:__read_once_size include/linux/compiler.h:254 [inline]
> > RIP: 0010:atomic_read arch/x86/include/asm/atomic.h:26 [inline]
> > RIP: 0010:rcu_dynticks_curr_cpu_in_eqs kernel/rcu/tree.c:350 [inline]
> > RIP: 0010:__rcu_is_watching kernel/rcu/tree.c:1133 [inline]
> > RIP: 0010:rcu_is_watching+0x83/0x110 kernel/rcu/tree.c:1147
> > RSP: 0000:ffff8801c391f120 EFLAGS: 00000a03 ORIG_RAX: ffffffffffffff10
> > RAX: dffffc0000000000 RBX: ffff8801c391f148 RCX: 0000000000000000
> > RDX: 0000000000000000 RSI: 000055edd4374000 RDI: ffff8801dbe1ae0c
> > RBP: ffff8801c391f1a0 R08: 0000000000000002 R09: 0000000000000000
> > R10: dffffc0000000000 R11: 0000000000000002 R12: 1ffff10038723e25
> > R13: ffff8801dbe1ae00 R14: ffff8801c391f680 R15: dffffc0000000000
> >  </IRQ>
> >  rcu_read_lock_held+0x87/0xc0 kernel/rcu/update.c:293
> >  radix_tree_deref_slot include/linux/radix-tree.h:238 [inline]
> >  filemap_map_pages+0x6d4/0x1570 mm/filemap.c:2335
> >  do_fault_around mm/memory.c:3231 [inline]
> >  do_read_fault mm/memory.c:3265 [inline]
> >  do_fault+0xbd5/0x2080 mm/memory.c:3370
> >  handle_pte_fault mm/memory.c:3600 [inline]
> >  __handle_mm_fault+0x1062/0x2cb0 mm/memory.c:3714
> >  handle_mm_fault+0x1e2/0x480 mm/memory.c:3751
> >  __do_page_fault+0x4f6/0xb60 arch/x86/mm/fault.c:1397
> >  do_page_fault+0x54/0x70 arch/x86/mm/fault.c:1460
> >  page_fault+0x28/0x30 arch/x86/entry/entry_64.S:1011
> > RIP: 0033:0x7f83172f2786
> > RSP: 002b:00007fffe859ae80 EFLAGS: 00010293
> > RAX: 000055edd4373040 RBX: 00007f83175111c8 RCX: 000055edd4373238
> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007f8317510970
> > RBP: 00007fffe859afd0 R08: 0000000000000009 R09: 0000000000000000
> > R10: 0000000000000064 R11: 0000000000000000 R12: 000055edd4373040
> > R13: 0000000000000000 R14: 00007fffe859afe8 R15: 0000000000000000
> 
> 
> This looks a false positive.
> An ICMP message can not be possibly fragmented.
> Following patch should fix the lockdep issue.
> 
> diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
> index bbe7f72db9c157ba2d6c5292637c2f58ad39a123..b3cdeec85f1f2c612c362590e828f50596a5c247 100644
> --- a/net/ipv4/ip_fragment.c
> +++ b/net/ipv4/ip_fragment.c
> @@ -198,6 +198,7 @@ static void ip_expire(unsigned long arg)
>  	qp = container_of((struct inet_frag_queue *) arg, struct ipq, q);
>  	net = container_of(qp->q.net, struct net, ipv4.frags);
>  
> +	rcu_read_lock();
>  	spin_lock(&qp->q.lock);
>  
>  	if (qp->q.flags & INET_FRAG_COMPLETE)
> @@ -207,7 +208,7 @@ static void ip_expire(unsigned long arg)
>  	__IP_INC_STATS(net, IPSTATS_MIB_REASMFAILS);
>  
>  	if (!inet_frag_evicting(&qp->q)) {
> -		struct sk_buff *head = qp->q.fragments;
> +		struct sk_buff *clone, *head = qp->q.fragments;
>  		const struct iphdr *iph;
>  		int err;
>  
> @@ -216,32 +217,40 @@ static void ip_expire(unsigned long arg)
>  		if (!(qp->q.flags & INET_FRAG_FIRST_IN) || !qp->q.fragments)
>  			goto out;
>  
> -		rcu_read_lock();
>  		head->dev = dev_get_by_index_rcu(net, qp->iif);
>  		if (!head->dev)
> -			goto out_rcu_unlock;
> +			goto out;
> +
>  
>  		/* skb has no dst, perform route lookup again */
>  		iph = ip_hdr(head);
>  		err = ip_route_input_noref(head, iph->daddr, iph->saddr,
>  					   iph->tos, head->dev);
>  		if (err)
> -			goto out_rcu_unlock;
> +			goto out;
>  
>  		/* Only an end host needs to send an ICMP
>  		 * "Fragment Reassembly Timeout" message, per RFC792.
>  		 */
>  		if (frag_expire_skip_icmp(qp->user) &&
>  		    (skb_rtable(head)->rt_type != RTN_LOCAL))
> -			goto out_rcu_unlock;
> +			goto out;
> +
> +		clone = skb_clone(head, GFP_ATOMIC);
>  
>  		/* Send an ICMP "Fragment Reassembly Timeout" message. */
> -		icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
> -out_rcu_unlock:
> -		rcu_read_unlock();
> +		if (clone) {
> +			spin_unlock(&qp->q.lock);
> +			icmp_send(clone, ICMP_TIME_EXCEEDED,
> +				  ICMP_EXC_FRAGTIME, 0);
> +			consume_skb(clone);
> +			goto out_rcu_unlock;
> +		}
>  	}
>  out:
>  	spin_unlock(&qp->q.lock);

I'm wondering if we really need to keep the fragment queue lock held
while sending the icmp packet ? we hold a reference to the struct, so
it can't be deleted, and AFAICS after ipq_kill() nobody else could
access/modify that queue.

That lock is there pretty much forever, but perhaps is only a leftover
and we can release it just after ipq_kill() ?

Paolo