From 061ff040710e9f6f043d1fa80b1b362d2845b17a Mon Sep 17 00:00:00 2001 From: Martin KaFai Lau Date: Thu, 29 Sep 2022 00:04:06 -0700 Subject: bpf: tcp: Stop bpf_setsockopt(TCP_CONGESTION) in init ops to recur itself When a bad bpf prog '.init' calls bpf_setsockopt(TCP_CONGESTION, "itself"), it will trigger this loop: .init => bpf_setsockopt(tcp_cc) => .init => bpf_setsockopt(tcp_cc) ... ... => .init => bpf_setsockopt(tcp_cc). It was prevented by the prog->active counter before but the prog->active detection cannot be used in struct_ops as explained in the earlier patch of the set. In this patch, the second bpf_setsockopt(tcp_cc) is not allowed in order to break the loop. This is done by using a bit of an existing 1 byte hole in tcp_sock to check if there is on-going bpf_setsockopt(TCP_CONGESTION) in this tcp_sock. Note that this essentially limits only the first '.init' can call bpf_setsockopt(TCP_CONGESTION) to pick a fallback cc (eg. peer does not support ECN) and the second '.init' cannot fallback to another cc. This applies even the second bpf_setsockopt(TCP_CONGESTION) will not cause a loop. Signed-off-by: Martin KaFai Lau Reviewed-by: Eric Dumazet Link: https://lore.kernel.org/r/20220929070407.965581-5-martin.lau@linux.dev Signed-off-by: Alexei Starovoitov --- include/linux/tcp.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include/linux/tcp.h') diff --git a/include/linux/tcp.h b/include/linux/tcp.h index a9fbe22732c3..3bdf687e2fb3 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -388,6 +388,12 @@ struct tcp_sock { u8 bpf_sock_ops_cb_flags; /* Control calling BPF programs * values defined in uapi/linux/tcp.h */ + u8 bpf_chg_cc_inprogress:1; /* In the middle of + * bpf_setsockopt(TCP_CONGESTION), + * it is to avoid the bpf_tcp_cc->init() + * to recur itself by calling + * bpf_setsockopt(TCP_CONGESTION, "itself"). + */ #define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) (TP->bpf_sock_ops_cb_flags & ARG) #else #define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) 0 -- cgit v1.2.1