From: Stanislav Fomichev <sdf.kernel@gmail.com>
To: Breno Leitao <leitao@debian.org>
Cc: David Ahern <dsahern@kernel.org>,
Ido Schimmel <idosch@nvidia.com>,
"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>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Eduard Zingerman <eddyz87@gmail.com>,
Kumar Kartikeya Dwivedi <memxor@gmail.com>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
Jiri Olsa <jolsa@kernel.org>,
Emil Tsalapatis <emil@etsalapatis.com>,
Ihor Solodrai <ihor.solodrai@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
Stanislav Fomichev <sdf@fomichev.me>,
Shuah Khan <shuah@kernel.org>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
bpf@vger.kernel.org, linux-kselftest@vger.kernel.org,
david.laight.linux@gmail.com, kernel-team@meta.com
Subject: Re: [PATCH net-next 1/6] ipv6: reject a negative optlen in do_ipv6_getsockopt()
Date: Fri, 25 Sep 2026 12:02:22 -0700 [thread overview]
Message-ID: <arbE6i8JZrOs-DO9@devvm7509.cco0.facebook.com> (raw)
In-Reply-To: <20260925-sockopt_expand_out_v2-v1-1-c3ef2e3bb5c0@debian.org>
On 09/25, Breno Leitao wrote:
> IPv4's do_ip_getsockopt() rejects a negative optlen right after reading
> it. do_ipv6_getsockopt() never has, and nothing downstream treats it as
> an error either: len is an int, but every consumer compares it unsigned,
> so -1 behaves as a huge value and each site clamps to its own reply
> size.
>
> len = min_t(unsigned int, sizeof(int), len);
>
> So getsockopt(fd, SOL_IPV6, IPV6_TCLASS, buf, &len) with len set to -1
> answers 4 bytes and reports 4, rather than failing.
>
> This is a bug ready to bite us in the near future, let's get this fixed.
>
> I've found this because testing the rest of the patch was returning
> inconsistency when optlen = -1.
If I can do getsockopt with len=-1 today and get 4 bytes back, isn't
that a uapi and we are gonna break someone?
next prev parent reply other threads:[~2026-09-25 19:02 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-25 15:55 [PATCH net-next 0/6] ipv4,ipv6: convert the getsockopt switches to sockopt_t Breno Leitao
2026-09-25 15:55 ` [PATCH net-next 1/6] ipv6: reject a negative optlen in do_ipv6_getsockopt() Breno Leitao
2026-09-25 19:02 ` Stanislav Fomichev [this message]
2026-09-27 6:53 ` David Laight
2026-09-29 12:14 ` Breno Leitao
2026-09-28 18:55 ` netdev-bot+sashiko
2026-09-25 15:55 ` [PATCH net-next 2/6] ipv6: mcast: convert ip6_mc_msfget() to sockopt_t Breno Leitao
2026-09-28 18:55 ` netdev-bot+sashiko
2026-09-25 15:55 ` [PATCH net-next 3/6] ipv4: igmp: convert ip_mc_gsfget() " Breno Leitao
2026-09-28 18:55 ` netdev-bot+sashiko
2026-09-25 15:55 ` [PATCH net-next 4/6] ipv4: convert do_ip_getsockopt() " Breno Leitao
2026-09-26 15:56 ` sashiko-bot
2026-09-28 18:55 ` netdev-bot+sashiko
2026-09-25 15:55 ` [PATCH net-next 5/6] ipv6: convert do_ipv6_getsockopt() " Breno Leitao
2026-09-28 18:55 ` netdev-bot+sashiko
2026-09-25 15:55 ` [PATCH net-next 6/6] selftests: net: getsockopt_iter: cover ip and ipv6 Breno Leitao
2026-09-28 18:55 ` netdev-bot+sashiko
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