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From: Martin KaFai Lau To: KaFai Wan Cc: edumazet@google.com, ncardwell@google.com, kuniyu@google.com, davem@davemloft.net, dsahern@kernel.org, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, shuah@kernel.org, sdf@fomichev.me, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, Quan Sun <2022090917019@std.uestc.edu.cn>, Yinhao Hu , Kaiyan Mei Subject: Re: [PATCH bpf-next 1/2] bpf: tcp: Reject TCP_NODELAY from BPF hdr opt callbacks Message-ID: <2026415171036.QLi9.martin.lau@linux.dev> References: <20260414112310.1285783-1-kafai.wan@linux.dev> <20260414112310.1285783-2-kafai.wan@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260414112310.1285783-2-kafai.wan@linux.dev> X-Migadu-Flow: FLOW_OUT On Tue, Apr 14, 2026 at 07:23:09PM +0800, KaFai Wan wrote: > A BPF_SOCK_OPS program can enable > BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG and then call > bpf_setsockopt(TCP_NODELAY) from BPF_SOCK_OPS_HDR_OPT_LEN_CB. > > That reaches __tcp_sock_set_nodelay(), which may call > tcp_push_pending_frames(). The transmit path then computes TCP > options again, re-enters bpf_skops_hdr_opt_len(), and invokes the > same BPF callback recursively. This can loop until the kernel > stack overflows. > > TCP_NODELAY is not safe from the header option callback context. > Reject it with -EOPNOTSUPP when TCP header option callbacks are > enabled on the socket, so the callback cannot recurse back into > tcp_push_pending_frames() through do_tcp_setsockopt(). > > Reported-by: Quan Sun <2022090917019@std.uestc.edu.cn> > Reported-by: Yinhao Hu > Reported-by: Kaiyan Mei > Closes: https://lore.kernel.org/bpf/d1d523c9-6901-4454-a183-94462b8f3e4e@std.uestc.edu.cn/ > Fixes: 7e41df5dbba2 ("bpf: Add a few optnames to bpf_setsockopt") > Signed-off-by: KaFai Wan > --- > net/ipv4/tcp.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > index 202a4e57a218..7ac4c98be19d 100644 > --- a/net/ipv4/tcp.c > +++ b/net/ipv4/tcp.c > @@ -4004,7 +4004,10 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname, > > switch (optname) { > case TCP_NODELAY: > - __tcp_sock_set_nodelay(sk, val); > + if (val && BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG)) It will break the syscall setsockopt and also break the existing bpf prog that calls bpf_setsockopt(TCP_NODELAY) in CB other than the BPF_SOCK_OPS_HDR_OPT_LEN_CB/BPF_SOCK_OPS_WRITE_HDR_OPT_CB. Lets brainstorm other options suggested on the list that have smaller blast radius. pw-bot: cr > + err = -EOPNOTSUPP; > + else > + __tcp_sock_set_nodelay(sk, val); > break; > > case TCP_THIN_LINEAR_TIMEOUTS: > -- > 2.43.0 >