From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Kohei Enju <kohei@enjuk.jp>, netdev@vger.kernel.org, bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Jesper Dangaard Brouer <hawk@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
Stanislav Fomichev <sdf@fomichev.me>,
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>,
KP Singh <kpsingh@kernel.org>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>, Jussi Maki <joamaki@gmail.com>,
kohei.enju@gmail.com, Kohei Enju <kohei@enjuk.jp>,
syzbot+10cc7f13760b31bd2e61@syzkaller.appspotmail.com
Subject: Re: [PATCH v3 bpf] bpf: devmap: fix stack-out-of-bounds write in get_upper_ifindexes()
Date: Tue, 24 Feb 2026 11:58:15 +0100 [thread overview]
Message-ID: <87ldgimmrc.fsf@toke.dk> (raw)
In-Reply-To: <20260224031556.38398-1-kohei@enjuk.jp>
Kohei Enju <kohei@enjuk.jp> writes:
> get_upper_ifindexes() iterates over all upper devices and writes their
> indices into an array without checking bounds.
>
> Also the callers assume that the max number of upper devices is
> MAX_NEST_DEV and allocate excluded_devices[1+MAX_NEST_DEV] on the stack,
> but that assumption is not correct and the number of upper devices could
> be larger than MAX_NEST_DEV (e.g., many macvlans), causing a
> stack-out-of-bounds write.
>
> Add a max parameter to get_upper_ifindexes() to avoid the issue.
> When there are too many upper devices, return -EOVERFLOW and abort the
> redirect.
>
> To reproduce, create more than MAX_NEST_DEV(8) macvlans on a device with
> an XDP program attached using BPF_F_BROADCAST | BPF_F_EXCLUDE_INGRESS.
> Then send a packet to the device to trigger the XDP redirect path.
>
> Reported-by: syzbot+10cc7f13760b31bd2e61@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/698c4ce3.050a0220.340abe.000b.GAE@google.com/T/
> Fixes: aeea1b86f936 ("bpf, devmap: Exclude XDP broadcast to master device")
> Signed-off-by: Kohei Enju <kohei@enjuk.jp>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
prev parent reply other threads:[~2026-02-24 10:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-24 3:15 [PATCH v3 bpf] bpf: devmap: fix stack-out-of-bounds write in get_upper_ifindexes() Kohei Enju
2026-02-24 3:21 ` Kohei Enju
2026-02-24 10:58 ` Toke Høiland-Jørgensen [this message]
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