netdev - Re: [PATCH bpf-next v2 3/5] tcp: Use skb__nullable in trace_tcp_send

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Message-ID: <CAADnVQ+nsUuQ+6rvEq7mYdE0vvqfZ-=hubcoGgUpprHA5P_mHA@mail.gmail.com>
Date: Fri, 6 Sep 2024 16:22:12 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Jakub Kicinski <kuba@...nel.org>, Jiri Olsa <jolsa@...nel.org>
Cc: Philo Lu <lulie@...ux.alibaba.com>, bpf <bpf@...r.kernel.org>, 
	Eric Dumazet <edumazet@...gle.com>, Steven Rostedt <rostedt@...dmis.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Eddy Z <eddyz87@...il.com>, 
	Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, 
	John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	"David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, Mykola Lysenko <mykolal@...com>, 
	Shuah Khan <shuah@...nel.org>, Maxime Coquelin <mcoquelin.stm32@...il.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Kui-Feng Lee <thinker.li@...il.com>, 
	Juntong Deng <juntong.deng@...look.com>, jrife@...gle.com, 
	Alan Maguire <alan.maguire@...cle.com>, Dave Marchevsky <davemarchevsky@...com>, 
	Daniel Xu <dxu@...uu.xyz>, Viktor Malik <vmalik@...hat.com>, 
	Cupertino Miranda <cupertino.miranda@...cle.com>, Matt Bobrowski <mattbobrowski@...gle.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Network Development <netdev@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 3/5] tcp: Use skb__nullable in trace_tcp_send_reset

On Fri, Sep 6, 2024 at 3:57 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Fri, 6 Sep 2024 15:41:47 -0700 Alexei Starovoitov wrote:
> > The urgency is now because the situation is dire.
> > The verifier assumes that skb is not null and will remove
> > if (!skb) check assuming that it's a dead code.
>
> Meaning verifier currently isn't ready for patch 4?
> Or we can crash 6.11-rc6 by attaching to a trace_tcp_send_reset()
> and doing
>         printf("%d\n", skb->len);
> ?

depends on the prog type and how it's attached, but yes :(
Without Philo's patches.

It was reported here:
https://lore.kernel.org/bpf/ZrCZS6nisraEqehw@jlelli-thinkpadt14gen4.remote.csb/

Jiri did the analysis. These files would need to be annotated:
include/trace/events/afs.h
include/trace/events/cachefiles.h
include/trace/events/ext4.h
include/trace/events/fib.h
include/trace/events/filelock.h
include/trace/events/host1x.h
include/trace/events/huge_memory.h
include/trace/events/kmem.h
include/trace/events/netfs.h
include/trace/events/power.h
include/trace/events/qdisc.h
include/trace/events/rxrpc.h
include/trace/events/sched.h
include/trace/events/sunrpc.h
include/trace/events/tcp.h
include/trace/events/tegra_apb_dma.h
include/trace/events/timer_migration.h
include/trace/events/writeback.h

which is 18 out of 160.

All other options are worse.