Re: [PATCH 4.14 106/143] sch_netem: restore skb->dev after dequeuing from the rbtree

[Sasha Levin]

On Fri, Nov 02, 2018 at 04:28:04PM -0700, Josh Hunt wrote:
> On Fri, Nov 2, 2018 at 12:00 PM Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > 4.14-stable review patch.  If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > Upstream commit bffa72cf7f9d ("net: sk_buff rbnode reorg") got
> > backported as commit 6b921536f170 ("net: sk_buff rbnode reorg") into the
> > v4.14.x-tree.
> >
> > However, the backport does not include the changes in sch_netem.c
> >
> > We need these, as otherwise the skb->dev pointer is not set when
> > dequeueing from the netem rbtree, resulting in a panic:
> >
> > [   15.427748] BUG: unable to handle kernel NULL pointer dereference at 00000000000000d0
> > [   15.428863] IP: netif_skb_features+0x24/0x230
> > [   15.429402] PGD 0 P4D 0
> > [   15.429733] Oops: 0000 [#1] SMP PTI
> > [   15.430169] Modules linked in:
> > [   15.430614] CPU: 3 PID: 0 Comm: swapper/3 Not tainted 4.14.77.mptcp #77
> > [   15.431497] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011
> > [   15.432568] task: ffff88042db19680 task.stack: ffffc90000070000
> > [   15.433356] RIP: 0010:netif_skb_features+0x24/0x230
> > [   15.433977] RSP: 0018:ffff88043fd83e70 EFLAGS: 00010286
> > [   15.434665] RAX: ffff880429ad80c0 RBX: ffff88042bd0e400 RCX: ffff880429ad8000
> > [   15.435585] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88042bd0e400
> > [   15.436551] RBP: ffff88042bd0e400 R08: ffff88042a4b6c9c R09: 0000000000000001
> > [   15.437485] R10: 0000000000000004 R11: 0000000000000000 R12: ffff88042c700000
> > [   15.438393] R13: ffff88042c700000 R14: ffff88042a4b6c00 R15: ffff88042c6bb000
> > [   15.439315] FS:  0000000000000000(0000) GS:ffff88043fd80000(0000) knlGS:0000000000000000
> > [   15.440314] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [   15.441084] CR2: 00000000000000d0 CR3: 000000042c374000 CR4: 00000000000006e0
> > [   15.442016] Call Trace:
> > [   15.442333]  <IRQ>
> > [   15.442596]  validate_xmit_skb+0x17/0x270
> > [   15.443134]  validate_xmit_skb_list+0x38/0x60
> > [   15.443698]  sch_direct_xmit+0x102/0x190
> > [   15.444198]  __qdisc_run+0xe3/0x240
> > [   15.444671]  net_tx_action+0x121/0x140
> > [   15.445177]  __do_softirq+0xe2/0x224
> > [   15.445654]  irq_exit+0xbf/0xd0
> > [   15.446072]  smp_apic_timer_interrupt+0x5d/0x90
> > [   15.446654]  apic_timer_interrupt+0x7d/0x90
> > [   15.447185]  </IRQ>
> > [   15.447460] RIP: 0010:native_safe_halt+0x2/0x10
> > [   15.447992] RSP: 0018:ffffc90000073f10 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff10
> > [   15.449008] RAX: ffffffff816667d0 RBX: ffffffff820946b0 RCX: 0000000000000000
> > [   15.449895] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> > [   15.450768] RBP: ffffffff82026940 R08: 00000004e858e5e1 R09: ffff88042a4b6d58
> > [   15.451643] R10: 0000000000000000 R11: 000000d0d56879bb R12: 0000000000000000
> > [   15.452478] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> > [   15.453340]  ? __sched_text_end+0x2/0x2
> > [   15.453835]  default_idle+0xf/0x20
> > [   15.454259]  do_idle+0x170/0x200
> > [   15.454653]  cpu_startup_entry+0x14/0x20
> > [   15.455142]  secondary_startup_64+0xa5/0xb0
> > [   15.455715] Code: 1f 84 00 00 00 00 00 55 53 48 89 fd 48 83 ec 08 8b 87 bc 00 00 00 48 8b 8f c0 00 00 00 0f b6 97 81 00 00 00 48 8b 77 10 48 01 c8 <48> 8b 9
> > [   15.458138] RIP: netif_skb_features+0x24/0x230 RSP: ffff88043fd83e70
> > [   15.458933] CR2: 00000000000000d0
> > [   15.459352] ---[ end trace 083925903ae60570 ]---
> >
> > Fixes: 6b921536f170 ("net: sk_buff rbnode reorg")
> > Cc: Stephen Hemminger <stephen@xxxxxxxxxxxxxxxxxx>
> > Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> > Cc: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx>
> > Cc: Wei Wang <weiwan@xxxxxxxxxx>
> > Cc: Willem de Bruijn <willemb@xxxxxxxxxx>
> > Signed-off-by: Christoph Paasch <cpaasch@xxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> >  net/sched/sch_netem.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
> > index 2a2ab6bfe5d8..3d325b840802 100644
> > --- a/net/sched/sch_netem.c
> > +++ b/net/sched/sch_netem.c
> > @@ -624,6 +624,10 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
> >                         skb->next = NULL;
> >                         skb->prev = NULL;
> >                         skb->tstamp = netem_skb_cb(skb)->tstamp_save;
> > +                       /* skb->dev shares skb->rbnode area,
> > +                        * we need to restore its value.
> > +                        */
> > +                       skb->dev = qdisc_dev(sch);
> >
> >  #ifdef CONFIG_NET_CLS_ACT
> >                         /*
> > --
> > 2.17.1
>
> I was seeing this crash on 4.14.78 and this patch fixes it.
>
> Thanks!

Thanks for confirming Josh!

--
Thanks,
Sasha