From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
syzbot <syzbot+cca39e6e84a367a7e6f6@syzkaller.appspotmail.com>
Cc: alexei.starovoitov@gmail.com, andrii@kernel.org, ast@kernel.org,
bpf@vger.kernel.org, daniel@iogearbox.net, davem@davemloft.net,
eddyz87@gmail.com, haoluo@google.com, hawk@kernel.org,
john.fastabend@gmail.com, jolsa@kernel.org, kpsingh@kernel.org,
kuba@kernel.org, linux-kernel@vger.kernel.org,
martin.lau@linux.dev, michal.switala@infogain.com,
netdev@vger.kernel.org, revest@google.com, sdf@fomichev.me,
sdf@google.com, song@kernel.org, syzkaller-bugs@googlegroups.com,
yonghong.song@linux.dev
Subject: Re: [syzbot] [bpf?] [net?] general protection fault in dev_map_enqueue (2)
Date: Fri, 20 Sep 2024 13:18:53 +0200 [thread overview]
Message-ID: <874j6aindu.fsf@toke.dk> (raw)
In-Reply-To: <20240902080232.wnhtxiWK@linutronix.de>
Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:
> On 2024-08-31 13:55:02 [-0700], syzbot wrote:
>> syzbot suspects this issue was fixed by commit:
>>
>> commit 401cb7dae8130fd34eb84648e02ab4c506df7d5e
>> Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> Date: Thu Jun 20 13:22:04 2024 +0000
>>
>> net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.
>>
>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=12597c63980000
>> start commit: 36534d3c5453 tcp: use signed arithmetic in tcp_rtx_probe0_..
>> git tree: bpf
>> kernel config: https://syzkaller.appspot.com/x/.config?x=333ebe38d43c42e2
>> dashboard link: https://syzkaller.appspot.com/bug?extid=cca39e6e84a367a7e6f6
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13390aea980000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10948741980000
>
> This looks like ri->tgt_value is a NULL pointer (dst in
> dev_map_enqueue()). The commit referenced by syz should not have fixed
> that.
> It is possible that there were leftovers in bpf_redirect_info (from a
> previous invocation) which were memset(,0,) during the switch from
> per-CPU to stack usage and now it does not trigger anymore.
Yes, I believe you are right. AFAICT, the original issue stems from the
SKB path and XDP path using the same numeric flag values in the
ri->flags field (specifically, BPF_F_BROADCAST == BPF_F_NEXTHOP). So if
bpf_redirect_neigh() was used and subsequently, an XDP redirect was
performed using the same bpf_redirect_info struct, the XDP path would
get confused and end up crashing. Now, with the stack-allocated
bpf_redirect_info, this sharing can no longer happen, so the crash
doesn't happen anymore.
However, different code paths using identically-numbered flag values
in the same struct field still seems like a bit of a mess, so I'll send
a patch to fix this just to be safe in case we ever move back to sharing
this data structure.
-Toke
next prev parent reply other threads:[~2024-09-20 11:19 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-27 0:44 [syzbot] [bpf?] [net?] general protection fault in dev_map_enqueue (2) syzbot
2024-06-09 11:34 ` syzbot
2024-07-08 16:03 ` [syzbot] bpf: Ensure BPF programs testing skb context initialization syzbot
2024-08-31 20:55 ` [syzbot] [bpf?] [net?] general protection fault in dev_map_enqueue (2) syzbot
2024-09-02 8:02 ` Sebastian Andrzej Siewior
2024-09-20 11:18 ` Toke Høiland-Jørgensen [this message]
[not found] <20240708160329.1868842-1-michal.switala@infogain.com>
2024-07-08 16:49 ` syzbot
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