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From: Christoph Paasch <christoph.paasch@gmail.com>
To: Vasily Averin <vvs@virtuozzo.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	"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: Wed, 25 Aug 2021 10:49:15 -0700	[thread overview]
Message-ID: <CALMXkpZYGC5HNkJAi4wCuawC-9CVNjN1LqO073YJvUF5ONwupA@mail.gmail.com> (raw)
In-Reply-To: <61da35a1-e609-02d5-609d-5228e184e43f@virtuozzo.com>

On Tue, Aug 24, 2021 at 10:22 AM Vasily Averin <vvs@virtuozzo.com> wrote:
>
> 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?

AFAICS, that's the problem around adjusting truesize. So, maybe "just"
refcount_add the increase of the truesize.

The below does fix the syzkaller bug for me and seems to do the right
thing overall. But I honestly think that this is becoming too hacky
and not worth it... and who knows what other corner-cases this now
exposes...

Maybe a revert is a better course of action?

---
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f9311762cc47..9cc18a0fdd1c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -71,6 +71,7 @@
 #include <net/mpls.h>
 #include <net/mptcp.h>
 #include <net/page_pool.h>
+#include <net/tcp.h>

 #include <linux/uaccess.h>
 #include <trace/events/skb.h>
@@ -1756,9 +1757,14 @@ int pskb_expand_head(struct sk_buff *skb, int
nhead, int ntail,
  * For the moment, we really care of rx path, or
  * when skb is orphaned (not attached to a socket).
  */
- if (!skb->sk || skb->destructor == sock_edemux)
+ if (!skb->sk || skb->destructor == sock_edemux || skb->destructor ==
tcp_wfree) {
  skb->truesize += size - osize;

+ if (skb->sk && skb->destructor == tcp_wfree) {
+ refcount_add(size - osize, &skb->sk->sk_wmem_alloc);
+ }
+ }
+
  return 0;

 nofrags:

  reply	other threads:[~2021-08-25 17:49 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
2021-08-25 17:49                                                           ` Christoph Paasch [this message]
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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