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| author | KaFai Wan <kafai.wan@linux.dev> | 2026-04-21 18:58:02 +0300 |
|---|---|---|
| committer | Martin KaFai Lau <martin.lau@kernel.org> | 2026-04-22 22:58:57 +0300 |
| commit | 54377fcab51f6f1f8807827d3751be42279e1a6a (patch) | |
| tree | 9701d312b26056ae6154bb69a97e7399777a9dc7 | |
| parent | 846c76ecc02973b05ae909dd4248c11bfa277fc1 (diff) | |
| download | linux-54377fcab51f6f1f8807827d3751be42279e1a6a.tar.xz | |
bpf: Reject TCP_NODELAY in bpf-tcp-cc
A BPF TCP congestion control program can call bpf_setsockopt() from
its callbacks. In current kernels, if it calls
bpf_setsockopt(TCP_NODELAY) from cwnd_event_tx_start(), the call can
re-enter the TCP transmit path before the outer tcp_transmit_skb()
has completed and advanced the send head.
This can re-trigger CA_EVENT_TX_START and lead to unbounded recursion:
tcp_transmit_skb()
-> tcp_event_data_sent()
-> tcp_ca_event(sk, CA_EVENT_TX_START)
-> cwnd_event_tx_start()
-> bpf_setsockopt(TCP_NODELAY)
-> tcp_push_pending_frames()
-> tcp_write_xmit()
-> tcp_transmit_skb()
This leads to unbounded recursion and can overflow the kernel stack.
Reject TCP_NODELAY with -EOPNOTSUPP for bpf-tcp-cc by introducing
a dedicated setsockopt proto for BPF_PROG_TYPE_STRUCT_OPS TCP
congestion control programs. To keep it simple, all tcp-cc ops is
rejected for TCP_NODELAY.
Fixes: 7e41df5dbba2 ("bpf: Add a few optnames to bpf_setsockopt")
Suggested-by: Martin KaFai Lau <martin.lau@linux.dev>
Signed-off-by: KaFai Wan <kafai.wan@linux.dev>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://patch.msgid.link/20260421155804.135786-3-kafai.wan@linux.dev
| -rw-r--r-- | include/linux/bpf.h | 1 | ||||
| -rw-r--r-- | net/core/filter.c | 24 | ||||
| -rw-r--r-- | net/ipv4/bpf_tcp_ca.c | 2 |
3 files changed, 26 insertions, 1 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index b4b703c90ca9..01e203964892 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -3725,6 +3725,7 @@ extern const struct bpf_func_proto bpf_for_each_map_elem_proto; extern const struct bpf_func_proto bpf_btf_find_by_name_kind_proto; extern const struct bpf_func_proto bpf_sk_setsockopt_proto; extern const struct bpf_func_proto bpf_sk_getsockopt_proto; +extern const struct bpf_func_proto bpf_sk_setsockopt_nodelay_proto; extern const struct bpf_func_proto bpf_unlocked_sk_setsockopt_proto; extern const struct bpf_func_proto bpf_unlocked_sk_getsockopt_proto; extern const struct bpf_func_proto bpf_find_vma_proto; diff --git a/net/core/filter.c b/net/core/filter.c index 96849f4c1fbc..2914f5330310 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -5688,6 +5688,30 @@ const struct bpf_func_proto bpf_sk_getsockopt_proto = { .arg5_type = ARG_CONST_SIZE, }; +BPF_CALL_5(bpf_sk_setsockopt_nodelay, struct sock *, sk, int, level, + int, optname, char *, optval, int, optlen) +{ + /* + * TCP_NODELAY triggers tcp_push_pending_frames() and re-enters + * CA_EVENT_TX_START in bpf_tcp_cc. + */ + if (level == SOL_TCP && optname == TCP_NODELAY) + return -EOPNOTSUPP; + + return _bpf_setsockopt(sk, level, optname, optval, optlen); +} + +const struct bpf_func_proto bpf_sk_setsockopt_nodelay_proto = { + .func = bpf_sk_setsockopt_nodelay, + .gpl_only = false, + .ret_type = RET_INTEGER, + .arg1_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON, + .arg2_type = ARG_ANYTHING, + .arg3_type = ARG_ANYTHING, + .arg4_type = ARG_PTR_TO_MEM | MEM_RDONLY, + .arg5_type = ARG_CONST_SIZE, +}; + BPF_CALL_5(bpf_unlocked_sk_setsockopt, struct sock *, sk, int, level, int, optname, char *, optval, int, optlen) { diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c index 008edc7f6688..791e15063237 100644 --- a/net/ipv4/bpf_tcp_ca.c +++ b/net/ipv4/bpf_tcp_ca.c @@ -168,7 +168,7 @@ bpf_tcp_ca_get_func_proto(enum bpf_func_id func_id, */ if (prog_ops_moff(prog) != offsetof(struct tcp_congestion_ops, release)) - return &bpf_sk_setsockopt_proto; + return &bpf_sk_setsockopt_nodelay_proto; return NULL; case BPF_FUNC_getsockopt: /* Since get/setsockopt is usually expected to |