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From: Vasily Averin <vvs@virtuozzo.com>
To: Eric Dumazet <eric.dumazet@gmail.com>,
	Christoph Paasch <christoph.paasch@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	David Ahern <dsahern@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>, netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel@openvz.org, Julian Wiedmann <jwi@linux.ibm.com>
Subject: Re: [PATCH NET-NEXT] ipv6: skb_expand_head() adjust skb->truesize incorrectly
Date: Tue, 24 Aug 2021 20:21:43 +0300	[thread overview]
Message-ID: <61da35a1-e609-02d5-609d-5228e184e43f@virtuozzo.com> (raw)
In-Reply-To: <4fe6edb4-a364-0e59-f902-9a362dd998d4@virtuozzo.com>

On 8/24/21 11:50 AM, Vasily Averin wrote:
> On 8/24/21 1:23 AM, Eric Dumazet wrote:
>> On 8/23/21 2:51 PM, Eric Dumazet wrote:
>>> On 8/23/21 2:45 PM, Eric Dumazet wrote:
>>>> On 8/23/21 10:25 AM, Christoph Paasch wrote:
>>>>> Hello,
>>>>>
>>>>> On Mon, Aug 23, 2021 at 12:56 AM Vasily Averin <vvs@virtuozzo.com> wrote:
>>>>>>
>>>>>> Christoph Paasch reports [1] about incorrect skb->truesize
>>>>>> after skb_expand_head() call in ip6_xmit.
>>>>>> This happen because skb_set_owner_w() for newly clone skb is called
>>>>>> too early, before pskb_expand_head() where truesize is adjusted for
>>>>>> (!skb-sk) case.
>>>>>>
>>>>>> [1] https://lkml.org/lkml/2021/8/20/1082
>>>>>>
>>>>>> Reported-by: Christoph Paasch <christoph.paasch@gmail.com>
>>>>>> Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
>>>>>> ---
>>>>>>  net/core/skbuff.c | 24 +++++++++++++-----------
>>>>>>  1 file changed, 13 insertions(+), 11 deletions(-)
>>>>>>
>>>>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>>>>>> index f931176..508d5c4 100644
>>>>>> --- a/net/core/skbuff.c
>>>>>> +++ b/net/core/skbuff.c
>>>>>> @@ -1803,6 +1803,8 @@ struct sk_buff *skb_realloc_headroom(struct sk_buff *skb, unsigned int headroom)
>>>>>>
>>>>>>  struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)
>>>>>>  {
>>>>>> +       struct sk_buff *oskb = skb;
>>>>>> +       struct sk_buff *nskb = NULL;
>>>>>>         int delta = headroom - skb_headroom(skb);
>>>>>>
>>>>>>         if (WARN_ONCE(delta <= 0,
>>>>>> @@ -1811,21 +1813,21 @@ struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)
>>>>>>
>>>>>>         /* pskb_expand_head() might crash, if skb is shared */
>>>>>>         if (skb_shared(skb)) {
>>>>>> -               struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
>>>>>> -
>>>>>> -               if (likely(nskb)) {
>>>>>> -                       if (skb->sk)
>>>>>> -                               skb_set_owner_w(nskb, skb->sk);
>>>>>> -                       consume_skb(skb);
>>>>>> -               } else {
>>>>>> -                       kfree_skb(skb);
>>>>>> -               }
>>>>>> +               nskb = skb_clone(skb, GFP_ATOMIC);
>>>>>>                 skb = nskb;
>>>>>>         }
>>>>>>         if (skb &&
>>>>>> -           pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
>>>>>> -               kfree_skb(skb);
>>>>>> +           pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC))
>>>>>>                 skb = NULL;
>>>>>> +
>>>>>> +       if (!skb) {
>>>>>> +               kfree_skb(oskb);
>>>>>> +               if (nskb)
>>>>>> +                       kfree_skb(nskb);
>>>>>> +       } else if (nskb) {
>>>>>> +               if (oskb->sk)
>>>>>> +                       skb_set_owner_w(nskb, oskb->sk);
>>>>>> +               consume_skb(oskb);
>>>>>
>>>>> sorry, this does not fix the problem. The syzkaller repro still
>>>>> triggers the WARN.
>>>>>
>>>>> When it happens, the skb in ip6_xmit() is not shared as it comes from
>>>>> __tcp_transmit_skb, where it is skb_clone()'d.
>>>>>
>>>>>
>>>>
>>>> Old code (in skb_realloc_headroom())
>>>> was first calling skb2 = skb_clone(skb, GFP_ATOMIC); 
>>>>
>>>> At this point, skb2->sk was NULL
>>>> So pskb_expand_head(skb2, SKB_DATA_ALIGN(delta), 0, ...) was able to tweak skb2->truesize
>>>>
>>>> I would try :
>>>>
>>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>>>> index f9311762cc475bd38d87c33e988d7c983b902e56..326749a8938637b044a616cc33b6a19ed191ac41 100644
>>>> --- a/net/core/skbuff.c
>>>> +++ b/net/core/skbuff.c
>>>> @@ -1804,6 +1804,7 @@ EXPORT_SYMBOL(skb_realloc_headroom);
>>>>  struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)
>>>>  {
>>>>         int delta = headroom - skb_headroom(skb);
>>>> +       struct sk_buff *oskb = NULL;
>>>>  
>>>>         if (WARN_ONCE(delta <= 0,
>>>>                       "%s is expecting an increase in the headroom", __func__))
>>>> @@ -1813,19 +1814,21 @@ struct sk_buff *skb_expand_head(struct sk_buff *skb, unsigned int headroom)
>>>>         if (skb_shared(skb)) {
>>>>                 struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
>>>>  
>>>> -               if (likely(nskb)) {
>>>> -                       if (skb->sk)
>>>> -                               skb_set_owner_w(nskb, skb->sk);
>>>> -                       consume_skb(skb);
>>>> -               } else {
>>>> +               if (unlikely(!nskb)) {
>>>>                         kfree_skb(skb);
>>>> +                       return NULL;
>>>>                 }
>>>> +               oskb = skb;
>>>>                 skb = nskb;
>>>>         }
>>>> -       if (skb &&
>>>> -           pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
>>>> +       if (pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
>>>>                 kfree_skb(skb);
>>>> -               skb = NULL;
>>>> +               kfree_skb(oskb);
>>>> +               return NULL;
>>>> +       }
>>>> +       if (oskb) {
>>>> +               skb_set_owner_w(skb, oskb->sk);
>>>> +               consume_skb(oskb);
>>>>         }
>>>>         return skb;
>>>>  }
>>>
>>>
>>> Oh well, probably not going to work.
>>>
>>> We have to find a way to properly increase skb->truesize, even if skb_clone() is _not_ called.
> 
> Can we adjust truesize outside pskb_expand_head()?
> Could you please explain why it can be not safe?

Do you mean truesize change should not break balance of sk->sk_wmem_alloc?

>> I also note that current use of skb_set_owner_w(), forcing skb->destructor to sock_wfree()
>> is probably breaking TCP Small queues, since original skb->destructor would be tcp_wfree() or __sock_wfree()
> 
> I agree, however as far as I understand it is separate and more global problem.
> 
> Thank you,
> 	Vasily Averin
> 


  reply	other threads:[~2021-08-24 17:24 UTC|newest]

Thread overview: 106+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <cover.1625665132.git.vvs@virtuozzo.com>
2021-07-07 14:04 ` [PATCH IPV6 1/1] ipv6: allocate enough headroom in ip6_finish_output2() Vasily Averin
2021-07-07 14:45   ` David Ahern
2021-07-07 16:42     ` Jakub Kicinski
2021-07-07 17:41       ` Eric Dumazet
2021-07-07 17:53         ` Vasily Averin
2021-07-07 18:30         ` Jakub Kicinski
2021-07-07 18:50           ` Eric Dumazet
2021-07-09  9:04         ` [PATCH IPV6 v2 0/4] " Vasily Averin
2021-07-12  6:44           ` [PATCH IPV6 v3 0/1] " Vasily Averin
     [not found]           ` <cover.1626069562.git.vvs@virtuozzo.com>
2021-07-12  6:45             ` [PATCH IPV6 v3 1/1] " Vasily Averin
2021-07-12 18:30               ` patchwork-bot+netdevbpf
2021-07-13  7:46               ` Vasily Averin
2021-07-13 12:01                 ` [PATCH NET v4 0/1] " Vasily Averin
     [not found]                 ` <cover.1626177047.git.vvs@virtuozzo.com>
2021-07-13 12:01                   ` [PATCH NET v4 1/1] " Vasily Averin
2021-07-18 10:44                     ` Vasily Averin
2021-07-18 15:22                       ` David Ahern
2021-07-18 17:04                       ` David Miller
2021-07-19  7:55                         ` [PATCH NET] ipv6: ip6_finish_output2: set sk into newly allocated nskb Vasily Averin
2021-07-20 10:10                           ` patchwork-bot+netdevbpf
2021-07-13 12:31                 ` [PATCH IPV6 v3 1/1] ipv6: allocate enough headroom in ip6_finish_output2() Vasily Averin
2021-07-12 13:26           ` [PATCH NET 0/7] skbuff: introduce pskb_realloc_headroom() Vasily Averin
     [not found]           ` <cover.1626093470.git.vvs@virtuozzo.com>
2021-07-12 13:26             ` [PATCH NET 1/7] " Vasily Averin
2021-07-12 17:53               ` Jakub Kicinski
2021-07-12 18:45                 ` Vasily Averin
2021-07-13 20:57                   ` [PATCH NET v2 0/7] skbuff: introduce skb_expand_head() Vasily Averin
2021-08-02  8:52                     ` [PATCH NET v3 " Vasily Averin
     [not found]                     ` <cover.1627891754.git.vvs@virtuozzo.com>
2021-08-02  8:52                       ` [PATCH NET v3 1/7] " Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 2/7] ipv6: use skb_expand_head in ip6_finish_output2 Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 3/7] ipv6: use skb_expand_head in ip6_xmit Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 4/7] ipv4: use skb_expand_head in ip_finish_output2 Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 5/7] vrf: use skb_expand_head in vrf_finish_output Vasily Averin
2021-08-05 11:55                         ` Julian Wiedmann
2021-08-05 12:55                           ` Vasily Averin
2021-08-06  7:49                           ` [PATCH NET v4 0/7] skbuff: introduce skb_expand_head() Vasily Averin
2021-08-06 10:14                             ` David Miller
2021-08-06 12:53                               ` [PATCH NET] vrf: fix null pointer dereference in vrf_finish_output() Vasily Averin
2021-08-06 22:42                                 ` Jakub Kicinski
2021-08-07  6:41                                   ` Vasily Averin
     [not found]                           ` <cover.1628235065.git.vvs@virtuozzo.com>
2021-08-06  7:49                             ` [PATCH NET v4 1/7] skbuff: introduce skb_expand_head() Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 2/7] ipv6: use skb_expand_head in ip6_finish_output2 Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 3/7] ipv6: use skb_expand_head in ip6_xmit Vasily Averin
     [not found]                               ` <CALMXkpaay1y=0tkbnskr4gf-HTMjJJsVryh4Prnej_ws-hJvBg@mail.gmail.com>
2021-08-20 22:44                                 ` Christoph Paasch
2021-08-21  6:21                                   ` Vasily Averin
2021-08-22 17:04                                     ` Christoph Paasch
2021-08-22 17:13                                       ` Christoph Paasch
2021-08-23  5:44                                         ` Vasily Averin
2021-08-23  5:59                                           ` Vasily Averin
2021-08-23  7:56                                             ` [PATCH NET-NEXT] ipv6: skb_expand_head() adjust skb->truesize incorrectly Vasily Averin
2021-08-23 17:25                                               ` Christoph Paasch
2021-08-23 21:45                                                 ` Eric Dumazet
2021-08-23 21:51                                                   ` Eric Dumazet
2021-08-23 22:23                                                     ` Eric Dumazet
2021-08-24  8:50                                                       ` Vasily Averin
2021-08-24 17:21                                                         ` Vasily Averin [this message]
2021-08-25 17:49                                                           ` Christoph Paasch
2021-08-29 12:59                                                             ` [PATCH v2] " Vasily Averin
2021-08-30  5:52                                                               ` [PATCH net-next " Vasily Averin
2021-08-30 16:01                                                               ` [PATCH " Eric Dumazet
2021-08-30 18:09                                                                 ` Vasily Averin
2021-08-30 18:37                                                                   ` Vasily Averin
2021-08-30 19:58                                                                   ` Eric Dumazet
2021-08-31 14:34                                                                     ` [PATCH net-next v3 RFC] " Vasily Averin
2021-08-31 19:38                                                                       ` Eric Dumazet
2021-09-01  6:20                                                                         ` Vasily Averin
2021-09-01  8:11                                                                           ` [PATCH net-next v4] " Vasily Averin
2021-09-01 16:58                                                                             ` Christoph Paasch
2021-09-01 19:17                                                                             ` Eric Dumazet
2021-09-02  3:59                                                                               ` Vasily Averin
2021-09-02  4:32                                                                                 ` Eric Dumazet
2021-09-02  4:48                                                                                   ` Eric Dumazet
2021-09-02  7:13                                                                                     ` Vasily Averin
2021-09-02  7:33                                                                                       ` Vasily Averin
2021-09-02  8:31                                                                                         ` Vasily Averin
2021-09-02 11:12                                                                                           ` [PATCH net-next v5] " Vasily Averin
2021-09-02 15:53                                                                                             ` Christoph Paasch
2021-09-02 16:32                                                                                               ` Vasily Averin
2021-09-06 18:01                                                                                                 ` [PATCH net v6] " Vasily Averin
2021-09-06 18:03                                                                                                   ` Vasily Averin
2021-08-27 15:23                                                       ` [PATCH NET-NEXT] ipv6: " Vasily Averin
2021-08-27 16:47                                                         ` Eric Dumazet
2021-08-28  8:01                                                           ` Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 4/7] ipv4: use skb_expand_head in ip_finish_output2 Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 5/7] vrf: use skb_expand_head in vrf_finish_output Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 6/7] ax25: use skb_expand_head Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 7/7] bpf: use skb_expand_head in bpf_out_neigh_v4/6 Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 6/7] ax25: use skb_expand_head Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 7/7] bpf: use skb_expand_head in bpf_out_neigh_v4/6 Vasily Averin
     [not found]                   ` <cover.1626206993.git.vvs@virtuozzo.com>
2021-07-13 20:57                     ` [PATCH NET v2 1/7] skbuff: introduce skb_expand_head() Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 2/7] ipv6: use skb_expand_head in ip6_finish_output2 Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 3/7] ipv6: use skb_expand_head in ip6_xmit Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 4/7] ipv4: use skb_expand_head in ip_finish_output2 Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 5/7] vrf: use skb_expand_head in vrf_finish_output Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 6/7] ax25: use skb_expand_head Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 7/7] bpf: use skb_expand_head in bpf_out_neigh_v4/6 Vasily Averin
2021-07-12 13:26             ` [PATCH NET 2/7] ipv6: use pskb_realloc_headroom in ip6_finish_output2 Vasily Averin
2021-07-12 13:26             ` [PATCH NET 3/7] ipv6: use pskb_realloc_headroom in ip6_xmit refactoring Vasily Averin
2021-07-12 13:27             ` [PATCH NET 4/7] ipv4: use pskb_realloc_headroom in ip_finish_output2 Vasily Averin
2021-07-12 13:27             ` [PATCH NET 5/7] vrf: use pskb_realloc_headroom in vrf_finish_output Vasily Averin
2021-07-12 13:27             ` [PATCH NET 6/7] ax25: use pskb_realloc_headroom Vasily Averin
2021-07-12 13:27             ` [PATCH NET 7/7] bpf: use pskb_realloc_headroom in bpf_out_neigh_v4/6 Vasily Averin
     [not found]         ` <cover.1625818825.git.vvs@virtuozzo.com>
2021-07-09  9:04           ` [PATCH IPV6 v2 1/4] ipv6: allocate enough headroom in ip6_finish_output2() Vasily Averin
2021-07-09 17:58             ` David Miller
2021-07-10  2:53               ` Vasily Averin
2021-07-09  9:04           ` [PATCH IPV6 v2 2/4] ipv6: use new helper skb_expand_head() in ip6_xmit() Vasily Averin
2021-07-09  9:05           ` [PATCH IPV6 v2 3/4] ipv6: ip6_finish_output2 refactoring Vasily Averin
2021-07-09  9:05           ` [PATCH IPV6 v2 4/4] ipv6: ip6_xmit refactoring Vasily Averin

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