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

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Message-ID: <20230906075730.6d61420a@kernel.org>
Date:   Wed, 6 Sep 2023 07:57:30 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eduard Zingerman <eddyz87@...il.com>
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, 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.

> 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")