Re: [PATCH net] net: Prevent invalid access to skb->prev in __qdisc_drop_all
On Thu, Nov 29, 2018 at 3:54 PM David Miller wrote: > > From: Eric Dumazet > Date: Thu, 29 Nov 2018 15:09:18 -0800 > > > diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c > > index > > 2c38e3d0792468162ee0dc4137f1400160ab9276..22cd46a600576f286803536d45875cd9d537cdca > > 100644 > > --- a/net/sched/sch_netem.c > > +++ b/net/sched/sch_netem.c > > @@ -431,6 +431,9 @@ static int netem_enqueue(struct sk_buff *skb, struct > > Qdisc *sch, > > int count = 1; > > int rc = NET_XMIT_SUCCESS; > > > > + /* Do not fool qdisc_drop_all() */ > > + skb->prev = NULL; > > + > > /* Random duplication */ > > if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor)) > > ++count; > > If this works I definitely prefer it to making the entire stack pay the > price to fix this crash. Yes, I tried it out and it works. Christoph
Re: [PATCH net] net: Prevent invalid access to skb->prev in __qdisc_drop_all
From: Christoph Paasch Date: Thu, 29 Nov 2018 15:45:19 -0800 > I can resubmit a patch. Please do after testing.
Re: [PATCH net] net: Prevent invalid access to skb->prev in __qdisc_drop_all
From: Eric Dumazet Date: Thu, 29 Nov 2018 15:09:18 -0800 > diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c > index > 2c38e3d0792468162ee0dc4137f1400160ab9276..22cd46a600576f286803536d45875cd9d537cdca > 100644 > --- a/net/sched/sch_netem.c > +++ b/net/sched/sch_netem.c > @@ -431,6 +431,9 @@ static int netem_enqueue(struct sk_buff *skb, struct > Qdisc *sch, > int count = 1; > int rc = NET_XMIT_SUCCESS; > > + /* Do not fool qdisc_drop_all() */ > + skb->prev = NULL; > + > /* Random duplication */ > if (q->duplicate && q->duplicate >= get_crandom(&q->dup_cor)) > ++count; If this works I definitely prefer it to making the entire stack pay the price to fix this crash.
Re: [PATCH net] net: Prevent invalid access to skb->prev in __qdisc_drop_all
On 29/11/18 - 15:09:18, Eric Dumazet wrote:
>
>
> On 11/29/2018 02:55 PM, Christoph Paasch wrote:
> > On 29/11/18 - 14:44:44, Eric Dumazet wrote:
> >>
> >>
> >> On 11/29/2018 02:27 PM, Christoph Paasch wrote:
> >>> There are places in the stack, where we access skb->prev directly and
> >>> modify it. Namely, __qdisc_drop_all().
> >>>
> >>> With commit 68d2f84a1368 ("net: gro: properly remove skb from list")
> >>> the skb-list handling has been changed to set skb->next to NULL and set
> >>> the list-poison on skb->prev.
> >>>
> >>> With that change, __qdisc_drop_all() will panic when it tries to
> >>> dereference skb->prev.
> >>>
> >>> Since commit 992cba7e276d ("net: Add and use skb_list_del_init().")
> >>> __list_del_entry is used, leaving skb->prev unchanged (thus,
> >>> pointing to the list-head if it's the first skb of the list).
> >>> This will make __qdisc_drop_all modify the next-pointer of the list-head
> >>> and result in a panic later on:
> >>>
> >>> [ 34.501053] general protection fault: [#1] SMP KASAN PTI
> >>> [ 34.501968] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.20.0-rc2.mptcp
> >>> #108
> >>> [ 34.502887] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> >>> BIOS 0.5.1 01/01/2011
> >>> [ 34.504074] RIP: 0010:dev_gro_receive+0x343/0x1f90
> >>> [ 34.504751] Code: e0 48 c1 e8 03 42 80 3c 30 00 0f 85 4a 1c 00 00 4d
> >>> 8b 24 24 4c 39 65 d0 0f 84 0a 04 00 00 49 8d 7c 24 38 48 89 f8 48 c1 e8
> >>> 03 <42> 0f b6 04 30 84 c0 74 08 3c 04
> >>> [ 34.507060] RSP: 0018:8883af507930 EFLAGS: 00010202
> >>> [ 34.507761] RAX: 0007 RBX: 8883970b2c80 RCX:
> >>> 111072e165a6
> >>> [ 34.508640] RDX: 111075867008 RSI: 8883ac338040 RDI:
> >>> 0038
> >>> [ 34.509493] RBP: 8883af5079d0 R08: 8883970b2d40 R09:
> >>> 0062
> >>> [ 34.510346] R10: 0034 R11: R12:
> >>>
> >>> [ 34.511215] R13: R14: dc00 R15:
> >>> 8883ac338008
> >>> [ 34.512082] FS: () GS:8883af50()
> >>> knlGS:
> >>> [ 34.513036] CS: 0010 DS: ES: CR0: 80050033
> >>> [ 34.513741] CR2: 55ccc3e9d020 CR3: 0003abf32000 CR4:
> >>> 06e0
> >>> [ 34.514593] Call Trace:
> >>> [ 34.514893]
> >>> [ 34.515157] napi_gro_receive+0x93/0x150
> >>> [ 34.515632] receive_buf+0x893/0x3700
> >>> [ 34.516094] ? __netif_receive_skb+0x1f/0x1a0
> >>> [ 34.516629] ? virtnet_probe+0x1b40/0x1b40
> >>> [ 34.517153] ? __stable_node_chain+0x4d0/0x850
> >>> [ 34.517684] ? kfree+0x9a/0x180
> >>> [ 34.518067] ? __kasan_slab_free+0x171/0x190
> >>> [ 34.518582] ? detach_buf+0x1df/0x650
> >>> [ 34.519061] ? lapic_next_event+0x5a/0x90
> >>> [ 34.519539] ? virtqueue_get_buf_ctx+0x280/0x7f0
> >>> [ 34.520093] virtnet_poll+0x2df/0xd60
> >>> [ 34.520533] ? receive_buf+0x3700/0x3700
> >>> [ 34.521027] ? qdisc_watchdog_schedule_ns+0xd5/0x140
> >>> [ 34.521631] ? htb_dequeue+0x1817/0x25f0
> >>> [ 34.522107] ? sch_direct_xmit+0x142/0xf30
> >>> [ 34.522595] ? virtqueue_napi_schedule+0x26/0x30
> >>> [ 34.523155] net_rx_action+0x2f6/0xc50
> >>> [ 34.523601] ? napi_complete_done+0x2f0/0x2f0
> >>> [ 34.524126] ? kasan_check_read+0x11/0x20
> >>> [ 34.524608] ? _raw_spin_lock+0x7d/0xd0
> >>> [ 34.525070] ? _raw_spin_lock_bh+0xd0/0xd0
> >>> [ 34.525563] ? kvm_guest_apic_eoi_write+0x6b/0x80
> >>> [ 34.526130] ? apic_ack_irq+0x9e/0xe0
> >>> [ 34.526567] __do_softirq+0x188/0x4b5
> >>> [ 34.527015] irq_exit+0x151/0x180
> >>> [ 34.527417] do_IRQ+0xdb/0x150
> >>> [ 34.527783] common_interrupt+0xf/0xf
> >>> [ 34.528223]
> >>>
> >>> This patch makes sure that skb->prev is also set to NULL when removing
> >>> it from the list.
> >>>
> >>> The bug is in v4.19.x as well, but the patch can't be backported easily.
> >>> I can post a follow-up for that.
> >>>
> >>> Cc: Prashant Bhole
> >>> Cc: Tyler Hicks
> >>> Fixes: 68d2f84a1368 ("net: gro: properly remove skb from list")
> >>> Signed-off-by: Christoph Paasch
> >>> ---
> >>> include/linux/skbuff.h | 1 +
> >>> 1 file changed, 1 insertion(+)
> >>>
> >>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> >>> index 0d1b2c3f127b..3bb3bfd390eb 100644
> >>> --- a/include/linux/skbuff.h
> >>> +++ b/include/linux/skbuff.h
> >>> @@ -1373,6 +1373,7 @@ static inline void skb_zcopy_abort(struct sk_buff
> >>> *skb)
> >>> static inline void skb_mark_not_on_list(struct sk_buff *skb)
> >>> {
> >>> skb->next = NULL;
> >>> + skb->prev = NULL;
> >>> }
> >>>
> >>> static inline void skb_list_del_init(struct sk_buff *skb)
> >>>
> >>
> >> skb_mark_not_on_list() is used in many place where we do not care of
> >> skb->prev
> >>
> >> What about fixing netem instead ?
> >
> > Yes, I have been looking at that and Alexey's patch which introduced the
> > access to skb->prev (cfr.: https://patchwork.
Re: [PATCH net] net: Prevent invalid access to skb->prev in __qdisc_drop_all
On 11/29/2018 02:55 PM, Christoph Paasch wrote:
> On 29/11/18 - 14:44:44, Eric Dumazet wrote:
>>
>>
>> On 11/29/2018 02:27 PM, Christoph Paasch wrote:
>>> There are places in the stack, where we access skb->prev directly and
>>> modify it. Namely, __qdisc_drop_all().
>>>
>>> With commit 68d2f84a1368 ("net: gro: properly remove skb from list")
>>> the skb-list handling has been changed to set skb->next to NULL and set
>>> the list-poison on skb->prev.
>>>
>>> With that change, __qdisc_drop_all() will panic when it tries to
>>> dereference skb->prev.
>>>
>>> Since commit 992cba7e276d ("net: Add and use skb_list_del_init().")
>>> __list_del_entry is used, leaving skb->prev unchanged (thus,
>>> pointing to the list-head if it's the first skb of the list).
>>> This will make __qdisc_drop_all modify the next-pointer of the list-head
>>> and result in a panic later on:
>>>
>>> [ 34.501053] general protection fault: [#1] SMP KASAN PTI
>>> [ 34.501968] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.20.0-rc2.mptcp
>>> #108
>>> [ 34.502887] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>>> 0.5.1 01/01/2011
>>> [ 34.504074] RIP: 0010:dev_gro_receive+0x343/0x1f90
>>> [ 34.504751] Code: e0 48 c1 e8 03 42 80 3c 30 00 0f 85 4a 1c 00 00 4d 8b
>>> 24 24 4c 39 65 d0 0f 84 0a 04 00 00 49 8d 7c 24 38 48 89 f8 48 c1 e8 03
>>> <42> 0f b6 04 30 84 c0 74 08 3c 04
>>> [ 34.507060] RSP: 0018:8883af507930 EFLAGS: 00010202
>>> [ 34.507761] RAX: 0007 RBX: 8883970b2c80 RCX:
>>> 111072e165a6
>>> [ 34.508640] RDX: 111075867008 RSI: 8883ac338040 RDI:
>>> 0038
>>> [ 34.509493] RBP: 8883af5079d0 R08: 8883970b2d40 R09:
>>> 0062
>>> [ 34.510346] R10: 0034 R11: R12:
>>>
>>> [ 34.511215] R13: R14: dc00 R15:
>>> 8883ac338008
>>> [ 34.512082] FS: () GS:8883af50()
>>> knlGS:
>>> [ 34.513036] CS: 0010 DS: ES: CR0: 80050033
>>> [ 34.513741] CR2: 55ccc3e9d020 CR3: 0003abf32000 CR4:
>>> 06e0
>>> [ 34.514593] Call Trace:
>>> [ 34.514893]
>>> [ 34.515157] napi_gro_receive+0x93/0x150
>>> [ 34.515632] receive_buf+0x893/0x3700
>>> [ 34.516094] ? __netif_receive_skb+0x1f/0x1a0
>>> [ 34.516629] ? virtnet_probe+0x1b40/0x1b40
>>> [ 34.517153] ? __stable_node_chain+0x4d0/0x850
>>> [ 34.517684] ? kfree+0x9a/0x180
>>> [ 34.518067] ? __kasan_slab_free+0x171/0x190
>>> [ 34.518582] ? detach_buf+0x1df/0x650
>>> [ 34.519061] ? lapic_next_event+0x5a/0x90
>>> [ 34.519539] ? virtqueue_get_buf_ctx+0x280/0x7f0
>>> [ 34.520093] virtnet_poll+0x2df/0xd60
>>> [ 34.520533] ? receive_buf+0x3700/0x3700
>>> [ 34.521027] ? qdisc_watchdog_schedule_ns+0xd5/0x140
>>> [ 34.521631] ? htb_dequeue+0x1817/0x25f0
>>> [ 34.522107] ? sch_direct_xmit+0x142/0xf30
>>> [ 34.522595] ? virtqueue_napi_schedule+0x26/0x30
>>> [ 34.523155] net_rx_action+0x2f6/0xc50
>>> [ 34.523601] ? napi_complete_done+0x2f0/0x2f0
>>> [ 34.524126] ? kasan_check_read+0x11/0x20
>>> [ 34.524608] ? _raw_spin_lock+0x7d/0xd0
>>> [ 34.525070] ? _raw_spin_lock_bh+0xd0/0xd0
>>> [ 34.525563] ? kvm_guest_apic_eoi_write+0x6b/0x80
>>> [ 34.526130] ? apic_ack_irq+0x9e/0xe0
>>> [ 34.526567] __do_softirq+0x188/0x4b5
>>> [ 34.527015] irq_exit+0x151/0x180
>>> [ 34.527417] do_IRQ+0xdb/0x150
>>> [ 34.527783] common_interrupt+0xf/0xf
>>> [ 34.528223]
>>>
>>> This patch makes sure that skb->prev is also set to NULL when removing
>>> it from the list.
>>>
>>> The bug is in v4.19.x as well, but the patch can't be backported easily.
>>> I can post a follow-up for that.
>>>
>>> Cc: Prashant Bhole
>>> Cc: Tyler Hicks
>>> Fixes: 68d2f84a1368 ("net: gro: properly remove skb from list")
>>> Signed-off-by: Christoph Paasch
>>> ---
>>> include/linux/skbuff.h | 1 +
>>> 1 file changed, 1 insertion(+)
>>>
>>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>>> index 0d1b2c3f127b..3bb3bfd390eb 100644
>>> --- a/include/linux/skbuff.h
>>> +++ b/include/linux/skbuff.h
>>> @@ -1373,6 +1373,7 @@ static inline void skb_zcopy_abort(struct sk_buff
>>> *skb)
>>> static inline void skb_mark_not_on_list(struct sk_buff *skb)
>>> {
>>> skb->next = NULL;
>>> + skb->prev = NULL;
>>> }
>>>
>>> static inline void skb_list_del_init(struct sk_buff *skb)
>>>
>>
>> skb_mark_not_on_list() is used in many place where we do not care of
>> skb->prev
>>
>> What about fixing netem instead ?
>
> Yes, I have been looking at that and Alexey's patch which introduced the
> access to skb->prev (cfr.: https://patchwork.ozlabs.org/patch/880717/).
>
> But then I thought that setting skb->prev to NULL is a less risky approach for
> -stable.
>
>
> How would you go about fixing netem instead?
>
> Because, from what I see we basically can enter netem_enqueue here with two
> different "
Re: [PATCH net] net: Prevent invalid access to skb->prev in __qdisc_drop_all
On 29/11/18 - 14:44:44, Eric Dumazet wrote:
>
>
> On 11/29/2018 02:27 PM, Christoph Paasch wrote:
> > There are places in the stack, where we access skb->prev directly and
> > modify it. Namely, __qdisc_drop_all().
> >
> > With commit 68d2f84a1368 ("net: gro: properly remove skb from list")
> > the skb-list handling has been changed to set skb->next to NULL and set
> > the list-poison on skb->prev.
> >
> > With that change, __qdisc_drop_all() will panic when it tries to
> > dereference skb->prev.
> >
> > Since commit 992cba7e276d ("net: Add and use skb_list_del_init().")
> > __list_del_entry is used, leaving skb->prev unchanged (thus,
> > pointing to the list-head if it's the first skb of the list).
> > This will make __qdisc_drop_all modify the next-pointer of the list-head
> > and result in a panic later on:
> >
> > [ 34.501053] general protection fault: [#1] SMP KASAN PTI
> > [ 34.501968] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.20.0-rc2.mptcp
> > #108
> > [ 34.502887] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> > 0.5.1 01/01/2011
> > [ 34.504074] RIP: 0010:dev_gro_receive+0x343/0x1f90
> > [ 34.504751] Code: e0 48 c1 e8 03 42 80 3c 30 00 0f 85 4a 1c 00 00 4d 8b
> > 24 24 4c 39 65 d0 0f 84 0a 04 00 00 49 8d 7c 24 38 48 89 f8 48 c1 e8 03
> > <42> 0f b6 04 30 84 c0 74 08 3c 04
> > [ 34.507060] RSP: 0018:8883af507930 EFLAGS: 00010202
> > [ 34.507761] RAX: 0007 RBX: 8883970b2c80 RCX:
> > 111072e165a6
> > [ 34.508640] RDX: 111075867008 RSI: 8883ac338040 RDI:
> > 0038
> > [ 34.509493] RBP: 8883af5079d0 R08: 8883970b2d40 R09:
> > 0062
> > [ 34.510346] R10: 0034 R11: R12:
> >
> > [ 34.511215] R13: R14: dc00 R15:
> > 8883ac338008
> > [ 34.512082] FS: () GS:8883af50()
> > knlGS:
> > [ 34.513036] CS: 0010 DS: ES: CR0: 80050033
> > [ 34.513741] CR2: 55ccc3e9d020 CR3: 0003abf32000 CR4:
> > 06e0
> > [ 34.514593] Call Trace:
> > [ 34.514893]
> > [ 34.515157] napi_gro_receive+0x93/0x150
> > [ 34.515632] receive_buf+0x893/0x3700
> > [ 34.516094] ? __netif_receive_skb+0x1f/0x1a0
> > [ 34.516629] ? virtnet_probe+0x1b40/0x1b40
> > [ 34.517153] ? __stable_node_chain+0x4d0/0x850
> > [ 34.517684] ? kfree+0x9a/0x180
> > [ 34.518067] ? __kasan_slab_free+0x171/0x190
> > [ 34.518582] ? detach_buf+0x1df/0x650
> > [ 34.519061] ? lapic_next_event+0x5a/0x90
> > [ 34.519539] ? virtqueue_get_buf_ctx+0x280/0x7f0
> > [ 34.520093] virtnet_poll+0x2df/0xd60
> > [ 34.520533] ? receive_buf+0x3700/0x3700
> > [ 34.521027] ? qdisc_watchdog_schedule_ns+0xd5/0x140
> > [ 34.521631] ? htb_dequeue+0x1817/0x25f0
> > [ 34.522107] ? sch_direct_xmit+0x142/0xf30
> > [ 34.522595] ? virtqueue_napi_schedule+0x26/0x30
> > [ 34.523155] net_rx_action+0x2f6/0xc50
> > [ 34.523601] ? napi_complete_done+0x2f0/0x2f0
> > [ 34.524126] ? kasan_check_read+0x11/0x20
> > [ 34.524608] ? _raw_spin_lock+0x7d/0xd0
> > [ 34.525070] ? _raw_spin_lock_bh+0xd0/0xd0
> > [ 34.525563] ? kvm_guest_apic_eoi_write+0x6b/0x80
> > [ 34.526130] ? apic_ack_irq+0x9e/0xe0
> > [ 34.526567] __do_softirq+0x188/0x4b5
> > [ 34.527015] irq_exit+0x151/0x180
> > [ 34.527417] do_IRQ+0xdb/0x150
> > [ 34.527783] common_interrupt+0xf/0xf
> > [ 34.528223]
> >
> > This patch makes sure that skb->prev is also set to NULL when removing
> > it from the list.
> >
> > The bug is in v4.19.x as well, but the patch can't be backported easily.
> > I can post a follow-up for that.
> >
> > Cc: Prashant Bhole
> > Cc: Tyler Hicks
> > Fixes: 68d2f84a1368 ("net: gro: properly remove skb from list")
> > Signed-off-by: Christoph Paasch
> > ---
> > include/linux/skbuff.h | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index 0d1b2c3f127b..3bb3bfd390eb 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -1373,6 +1373,7 @@ static inline void skb_zcopy_abort(struct sk_buff
> > *skb)
> > static inline void skb_mark_not_on_list(struct sk_buff *skb)
> > {
> > skb->next = NULL;
> > + skb->prev = NULL;
> > }
> >
> > static inline void skb_list_del_init(struct sk_buff *skb)
> >
>
> skb_mark_not_on_list() is used in many place where we do not care of skb->prev
>
> What about fixing netem instead ?
Yes, I have been looking at that and Alexey's patch which introduced the
access to skb->prev (cfr.: https://patchwork.ozlabs.org/patch/880717/).
But then I thought that setting skb->prev to NULL is a less risky approach for
-stable.
How would you go about fixing netem instead?
Because, from what I see we basically can enter netem_enqueue here with two
different "types" of skb's. The ones where skb->prev points to the tail of
the list of
Re: [PATCH net] net: Prevent invalid access to skb->prev in __qdisc_drop_all
On 11/29/2018 02:27 PM, Christoph Paasch wrote:
> There are places in the stack, where we access skb->prev directly and
> modify it. Namely, __qdisc_drop_all().
>
> With commit 68d2f84a1368 ("net: gro: properly remove skb from list")
> the skb-list handling has been changed to set skb->next to NULL and set
> the list-poison on skb->prev.
>
> With that change, __qdisc_drop_all() will panic when it tries to
> dereference skb->prev.
>
> Since commit 992cba7e276d ("net: Add and use skb_list_del_init().")
> __list_del_entry is used, leaving skb->prev unchanged (thus,
> pointing to the list-head if it's the first skb of the list).
> This will make __qdisc_drop_all modify the next-pointer of the list-head
> and result in a panic later on:
>
> [ 34.501053] general protection fault: [#1] SMP KASAN PTI
> [ 34.501968] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.20.0-rc2.mptcp #108
> [ 34.502887] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> 0.5.1 01/01/2011
> [ 34.504074] RIP: 0010:dev_gro_receive+0x343/0x1f90
> [ 34.504751] Code: e0 48 c1 e8 03 42 80 3c 30 00 0f 85 4a 1c 00 00 4d 8b 24
> 24 4c 39 65 d0 0f 84 0a 04 00 00 49 8d 7c 24 38 48 89 f8 48 c1 e8 03 <42> 0f
> b6 04 30 84 c0 74 08 3c 04
> [ 34.507060] RSP: 0018:8883af507930 EFLAGS: 00010202
> [ 34.507761] RAX: 0007 RBX: 8883970b2c80 RCX:
> 111072e165a6
> [ 34.508640] RDX: 111075867008 RSI: 8883ac338040 RDI:
> 0038
> [ 34.509493] RBP: 8883af5079d0 R08: 8883970b2d40 R09:
> 0062
> [ 34.510346] R10: 0034 R11: R12:
>
> [ 34.511215] R13: R14: dc00 R15:
> 8883ac338008
> [ 34.512082] FS: () GS:8883af50()
> knlGS:
> [ 34.513036] CS: 0010 DS: ES: CR0: 80050033
> [ 34.513741] CR2: 55ccc3e9d020 CR3: 0003abf32000 CR4:
> 06e0
> [ 34.514593] Call Trace:
> [ 34.514893]
> [ 34.515157] napi_gro_receive+0x93/0x150
> [ 34.515632] receive_buf+0x893/0x3700
> [ 34.516094] ? __netif_receive_skb+0x1f/0x1a0
> [ 34.516629] ? virtnet_probe+0x1b40/0x1b40
> [ 34.517153] ? __stable_node_chain+0x4d0/0x850
> [ 34.517684] ? kfree+0x9a/0x180
> [ 34.518067] ? __kasan_slab_free+0x171/0x190
> [ 34.518582] ? detach_buf+0x1df/0x650
> [ 34.519061] ? lapic_next_event+0x5a/0x90
> [ 34.519539] ? virtqueue_get_buf_ctx+0x280/0x7f0
> [ 34.520093] virtnet_poll+0x2df/0xd60
> [ 34.520533] ? receive_buf+0x3700/0x3700
> [ 34.521027] ? qdisc_watchdog_schedule_ns+0xd5/0x140
> [ 34.521631] ? htb_dequeue+0x1817/0x25f0
> [ 34.522107] ? sch_direct_xmit+0x142/0xf30
> [ 34.522595] ? virtqueue_napi_schedule+0x26/0x30
> [ 34.523155] net_rx_action+0x2f6/0xc50
> [ 34.523601] ? napi_complete_done+0x2f0/0x2f0
> [ 34.524126] ? kasan_check_read+0x11/0x20
> [ 34.524608] ? _raw_spin_lock+0x7d/0xd0
> [ 34.525070] ? _raw_spin_lock_bh+0xd0/0xd0
> [ 34.525563] ? kvm_guest_apic_eoi_write+0x6b/0x80
> [ 34.526130] ? apic_ack_irq+0x9e/0xe0
> [ 34.526567] __do_softirq+0x188/0x4b5
> [ 34.527015] irq_exit+0x151/0x180
> [ 34.527417] do_IRQ+0xdb/0x150
> [ 34.527783] common_interrupt+0xf/0xf
> [ 34.528223]
>
> This patch makes sure that skb->prev is also set to NULL when removing
> it from the list.
>
> The bug is in v4.19.x as well, but the patch can't be backported easily.
> I can post a follow-up for that.
>
> Cc: Prashant Bhole
> Cc: Tyler Hicks
> Fixes: 68d2f84a1368 ("net: gro: properly remove skb from list")
> Signed-off-by: Christoph Paasch
> ---
> include/linux/skbuff.h | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 0d1b2c3f127b..3bb3bfd390eb 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -1373,6 +1373,7 @@ static inline void skb_zcopy_abort(struct sk_buff *skb)
> static inline void skb_mark_not_on_list(struct sk_buff *skb)
> {
> skb->next = NULL;
> + skb->prev = NULL;
> }
>
> static inline void skb_list_del_init(struct sk_buff *skb)
>
skb_mark_not_on_list() is used in many place where we do not care of skb->prev
What about fixing netem instead ?
