On Mon, Oct 20, 2025 at 02:04 PM +08, Jiayuan Chen wrote:
MPTCP creates subflows for data transmission, and these sockets should not be added to sockmap because MPTCP sets specialized data_ready handlers that would be overridden by sockmap.
Additionally, for the parent socket of MPTCP subflows (plain TCP socket), MPTCP sk requires specific protocol handling that conflicts with sockmap's operation(mptcp_prot).
This patch adds proper checks to reject MPTCP subflows and their parent sockets from being added to sockmap, while preserving compatibility with reuseport functionality for listening MPTCP sockets.
Fixes: 0b4f33def7bb ("mptcp: fix tcp fallback crash") Signed-off-by: Jiayuan Chen jiayuan.chen@linux.dev
net/core/sock_map.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/net/core/sock_map.c b/net/core/sock_map.c index 5947b38e4f8b..da21deb970b3 100644 --- a/net/core/sock_map.c +++ b/net/core/sock_map.c @@ -535,6 +535,15 @@ static bool sock_map_redirect_allowed(const struct sock *sk) static bool sock_map_sk_is_suitable(const struct sock *sk) {
- if ((sk_is_tcp(sk) && sk_is_mptcp(sk)) /* subflow */ ||
(sk->sk_protocol == IPPROTO_MPTCP && sk->sk_state != TCP_LISTEN)) {/* Disallow MPTCP subflows and their parent socket.* However, a TCP_LISTEN MPTCP socket is permitted because* sockmap can also serve for reuseport socket selection.*/pr_err_once("sockmap: MPTCP sockets are not supported\n");return false;- } return !!sk->sk_prot->psock_update_sk_prot;
}
You're checking sk_state without sk_lock held. That doesn't seem right. Take a look how we always call sock_map_sk_state_allowed() after grabbing the lock.
Same might apply to sk_is_mptcp(). Please double check.