linux-kernel - Re: [syzbot] [bpf?] general protection fault in bpf_prog_offload_verifier

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Date:   Wed, 06 Sep 2023 21:00:37 +0300
From:   Eduard Zingerman <eddyz87@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     syzbot <syzbot+291100dcb32190ec02a8@...kaller.appspotmail.com>,
        andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
        daniel@...earbox.net, davem@...emloft.net, haoluo@...gle.com,
        hawk@...nel.org, john.fastabend@...il.com, jolsa@...nel.org,
        kpsingh@...nel.org, linux-kernel@...r.kernel.org,
        martin.lau@...ux.dev, netdev@...r.kernel.org, sdf@...gle.com,
        song@...nel.org, syzkaller-bugs@...glegroups.com,
        yonghong.song@...ux.dev
Subject: Re: [syzbot] [bpf?] general protection fault in
 bpf_prog_offload_verifier_prep

On Wed, 2023-09-06 at 07:57 -0700, Jakub Kicinski wrote:
> On Wed, 06 Sep 2023 16:50:23 +0300 Eduard Zingerman wrote:
> > diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
> > index 3e4f2ec1af06..302e38bffffa 100644
> > --- a/kernel/bpf/offload.c
> > +++ b/kernel/bpf/offload.c
> > @@ -199,12 +199,11 @@ static int __bpf_prog_dev_bound_init(struct bpf_prog *prog, struct net_device *n
> >         offload->netdev = netdev;
> >  
> >         ondev = bpf_offload_find_netdev(offload->netdev);
> > +       if (bpf_prog_is_offloaded(prog->aux) && (!ondev || !ondev->offdev)) {
> > +               err = -EINVAL;
> > +               goto err_free;
> > +       }
> >         if (!ondev) {
> > -               if (bpf_prog_is_offloaded(prog->aux)) {
> > -                       err = -EINVAL;
> > -                       goto err_free;
> > -               }
> > -
> >                 /* When only binding to the device, explicitly
> >                  * create an entry in the hashtable.
> >                  */
> 
> LGTM, FWIW.

Thanks, I'll wrap it up as a proper patch with a test.

> 
> > With the following reasoning: for offloaded programs offload device
> > should exist and it should not be a fake device create in !ondev branch.
> > 
> > Stanislav, could you please take a look? I think this is related to commit:
> > 2b3486bc2d23 ("bpf: Introduce device-bound XDP programs")