Re: [PATCH ipsec] esp: remove the skb from the chain when it's enqueued in cryptd_wq

[Xin Long <lucien.xin@gmail.com>]

On Mon, Mar 9, 2020 at 6:07 PM Mika Penttilä <mika.penttila@nextfour.com> wrote:
>
>
> Hi!
>
> On 4.3.2020 10.51, Xin Long wrote:
> > Xiumei found a panic in esp offload:
> >
> >   BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
> >   RIP: 0010:esp_output_done+0x101/0x160 [esp4]
> >   Call Trace:
> >    ? esp_output+0x180/0x180 [esp4]
> >    cryptd_aead_crypt+0x4c/0x90
> >    cryptd_queue_worker+0x6e/0xa0
> >    process_one_work+0x1a7/0x3b0
> >    worker_thread+0x30/0x390
> >    ? create_worker+0x1a0/0x1a0
> >    kthread+0x112/0x130
> >    ? kthread_flush_work_fn+0x10/0x10
> >    ret_from_fork+0x35/0x40
> >
> > It was caused by that skb secpath is used in esp_output_done() after it's
> > been released elsewhere.
> >
> > The tx path for esp offload is:
> >
> >   __dev_queue_xmit()->
> >     validate_xmit_skb_list()->
> >       validate_xmit_xfrm()->
> >         esp_xmit()->
> >           esp_output_tail()->
> >             aead_request_set_callback(esp_output_done) <--[1]
> >             crypto_aead_encrypt()  <--[2]
> >
> > In [1], .callback is set, and in [2] it will trigger the worker schedule,
> > later on a kernel thread will call .callback(esp_output_done), as the call
> > trace shows.
> >
> > But in validate_xmit_xfrm():
> >
> >   skb_list_walk_safe(skb, skb2, nskb) {
> >     ...
> >     err = x->type_offload->xmit(x, skb2, esp_features);  [esp_xmit]
> >     ...
> >   }
> >
> > When the err is -EINPROGRESS, which means this skb2 will be enqueued and
> > later gets encrypted and sent out by .callback later in a kernel thread,
> > skb2 should be removed fromt skb chain. Otherwise, it will get processed
> > again outside validate_xmit_xfrm(), which could release skb secpath, and
> > cause the panic above.
> >
> > This patch is to remove the skb from the chain when it's enqueued in
> > cryptd_wq. While at it, remove the unnecessary 'if (!skb)' check.
> >
> > Fixes: 3dca3f38cfb8 ("xfrm: Separate ESP handling from segmentation for GRO packets.")
> > Reported-by: Xiumei Mu <xmu@redhat.com>
> > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > ---
> >  net/xfrm/xfrm_device.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/xfrm/xfrm_device.c b/net/xfrm/xfrm_device.c
> > index 3231ec6..e2db468 100644
> > --- a/net/xfrm/xfrm_device.c
> > +++ b/net/xfrm/xfrm_device.c
> > @@ -78,8 +78,8 @@ struct sk_buff *validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t featur
> >       int err;
> >       unsigned long flags;
> >       struct xfrm_state *x;
> > -     struct sk_buff *skb2, *nskb;
> >       struct softnet_data *sd;
> > +     struct sk_buff *skb2, *nskb, *pskb = NULL;
> >       netdev_features_t esp_features = features;
> >       struct xfrm_offload *xo = xfrm_offload(skb);
> >       struct sec_path *sp;
> > @@ -168,14 +168,14 @@ struct sk_buff *validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t featur
> >               } else {
> >                       if (skb == skb2)
> >                               skb = nskb;
> > -
> > -                     if (!skb)
> > -                             return NULL;
> > +                     else
> > +                             pskb->next = nskb;
>
> pskb can be NULL on the first round?
On the 1st round, skb == skb2.

>
>
>
> >                       continue;
> >               }
> >
> >               skb_push(skb2, skb2->data - skb_mac_header(skb2));
> > +             pskb = skb2;
> >       }
> >
> >       return skb;
>