From: Daniel Borkmann <daniel@iogearbox.net>
To: Jiayuan Chen <jiayuan.chen@linux.dev>, netdev@vger.kernel.org
Cc: syzbot+80e046b8da2820b6ba73@syzkaller.appspotmail.com,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@fomichev.me>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Simon Horman <horms@kernel.org>,
Jesper Dangaard Brouer <hawk@kernel.org>,
Shuah Khan <shuah@kernel.org>, Jussi Maki <joamaki@gmail.com>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org,
Nikolay Aleksandrov <razor@blackwall.org>
Subject: Re: [PATCH net v6 1/2] net, bpf: fix null-ptr-deref in xdp_master_redirect() for down master
Date: Fri, 10 Apr 2026 17:42:10 +0200 [thread overview]
Message-ID: <917b37eb-af81-41fc-bc60-ce37642f4bd9@iogearbox.net> (raw)
In-Reply-To: <20260410113726.368111-2-jiayuan.chen@linux.dev>
On 4/10/26 1:37 PM, Jiayuan Chen wrote:
> syzkaller reported a kernel panic in bond_rr_gen_slave_id() reached via
> xdp_master_redirect(). Full decoded trace:
>
> https://syzkaller.appspot.com/bug?extid=80e046b8da2820b6ba73
>
> bond_rr_gen_slave_id() dereferences bond->rr_tx_counter, a per-CPU
> counter that bonding only allocates in bond_open() when the mode is
> round-robin. If the bond device was never brought up, rr_tx_counter
> stays NULL.
>
> The XDP redirect path can still reach that code on a bond that was
> never opened: bpf_master_redirect_enabled_key is a global static key,
> so as soon as any bond device has native XDP attached, the
> XDP_TX -> xdp_master_redirect() interception is enabled for every
> slave system-wide. The path xdp_master_redirect() ->
> bond_xdp_get_xmit_slave() -> bond_xdp_xmit_roundrobin_slave_get() ->
> bond_rr_gen_slave_id() then runs against a bond that has no
> rr_tx_counter and crashes.
>
> Fix this in the generic xdp_master_redirect() by refusing to call into
> the master's ->ndo_xdp_get_xmit_slave() when the master device is not
> up. IFF_UP is only set after ->ndo_open() has successfully returned,
> so this reliably excludes masters whose XDP state has not been fully
> initialized. Drop the frame with XDP_ABORTED so the exception is
> visible via trace_xdp_exception() rather than silently falling through.
> This is not specific to bonding: any current or future master that
> defers XDP state allocation to ->ndo_open() is protected.
>
> Fixes: 879af96ffd72 ("net, core: Add support for XDP redirection to slave device")
> Reported-by: syzbot+80e046b8da2820b6ba73@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/698f84c6.a70a0220.2c38d7.00cc.GAE@google.com/T/
> Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
next prev parent reply other threads:[~2026-04-10 15:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-10 11:37 [PATCH net v6 0/2] net,bpf: fix null-ptr-deref in xdp_master_redirect() for bonding and add selftest Jiayuan Chen
2026-04-10 11:37 ` [PATCH net v6 1/2] net, bpf: fix null-ptr-deref in xdp_master_redirect() for down master Jiayuan Chen
2026-04-10 15:42 ` Daniel Borkmann [this message]
2026-04-10 11:37 ` [PATCH net v6 2/2] selftests/bpf: add test for xdp_master_redirect with bond not up Jiayuan Chen
2026-04-10 16:28 ` Daniel Borkmann
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