From: Jiayuan Chen jiayuan.chen@linux.dev
[ Upstream commit c77b3b79a92e3345aa1ee296180d1af4e7031f8f ]
The sockmap feature allows bpf syscall from userspace, or based on bpf sockops, replacing the sk_prot of sockets during protocol stack processing with sockmap's custom read/write interfaces. ''' tcp_rcv_state_process() syn_recv_sock()/subflow_syn_recv_sock() tcp_init_transfer(BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB) bpf_skops_established <== sockops bpf_sock_map_update(sk) <== call bpf helper tcp_bpf_update_proto() <== update sk_prot '''
When the server has MPTCP enabled but the client sends a TCP SYN without MPTCP, subflow_syn_recv_sock() performs a fallback on the subflow, replacing the subflow sk's sk_prot with the native sk_prot. ''' subflow_syn_recv_sock() subflow_ulp_fallback() subflow_drop_ctx() mptcp_subflow_ops_undo_override() '''
Then, this subflow can be normally used by sockmap, which replaces the native sk_prot with sockmap's custom sk_prot. The issue occurs when the user executes accept::mptcp_stream_accept::mptcp_fallback_tcp_ops(). Here, it uses sk->sk_prot to compare with the native sk_prot, but this is incorrect when sockmap is used, as we may incorrectly set sk->sk_socket->ops.
This fix uses the more generic sk_family for the comparison instead.
Additionally, this also prevents a WARNING from occurring:
result from ./scripts/decode_stacktrace.sh: ------------[ cut here ]------------ WARNING: CPU: 0 PID: 337 at net/mptcp/protocol.c:68 mptcp_stream_accept \ (net/mptcp/protocol.c:4005) Modules linked in: ...
PKRU: 55555554 Call Trace: <TASK> do_accept (net/socket.c:1989) __sys_accept4 (net/socket.c:2028 net/socket.c:2057) __x64_sys_accept (net/socket.c:2067) x64_sys_call (arch/x86/entry/syscall_64.c:41) do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) RIP: 0033:0x7f87ac92b83d
---[ end trace 0000000000000000 ]---
Fixes: 0b4f33def7bb ("mptcp: fix tcp fallback crash") Signed-off-by: Jiayuan Chen jiayuan.chen@linux.dev Signed-off-by: Martin KaFai Lau martin.lau@kernel.org Reviewed-by: Jakub Sitnicki jakub@cloudflare.com Reviewed-by: Matthieu Baerts (NGI0) matttbe@kernel.org Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20251111060307.194196-3-jiayuan.chen@linux.dev [ applied fix to mptcp_is_tcpsk() instead of mptcp_fallback_tcp_ops() ] Signed-off-by: Sasha Levin sashal@kernel.org --- net/mptcp/protocol.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 490fd8b188894..f758fde0565a2 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -77,8 +77,9 @@ static u64 mptcp_wnd_end(const struct mptcp_sock *msk) static bool mptcp_is_tcpsk(struct sock *sk) { struct socket *sock = sk->sk_socket; + unsigned short family = READ_ONCE(sk->sk_family);
- if (unlikely(sk->sk_prot == &tcp_prot)) { + if (unlikely(family == AF_INET)) { /* we are being invoked after mptcp_accept() has * accepted a non-mp-capable flow: sk is a tcp_sk, * not an mptcp one. @@ -89,7 +90,7 @@ static bool mptcp_is_tcpsk(struct sock *sk) sock->ops = &inet_stream_ops; return true; #if IS_ENABLED(CONFIG_MPTCP_IPV6) - } else if (unlikely(sk->sk_prot == &tcpv6_prot)) { + } else if (unlikely(family == AF_INET6)) { sock->ops = &inet6_stream_ops; return true; #endif