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Tue, 11 Aug 2026 14:51:47 -0700 (PDT) Received: from LAPTOP-N5EO9J2L.localdomain ([106.202.115.11]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-141245a9f70sm3672334c88.15.2026.08.11.14.51.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Aug 2026 14:51:47 -0700 (PDT) From: Harshit Varu To: netdev@vger.kernel.org Cc: mptcp@lists.linux.dev, matttbe@kernel.org, martineau@kernel.org, security@kernel.org, Harshit Varu , stable@vger.kernel.org Subject: [PATCH mptcp] mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction Date: Wed, 12 Aug 2026 03:21:35 +0530 Message-ID: <20260811215135.87756-1-harshitvaru666@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" mptcp_token_join_cookie_init_state() restores remote_nonce, local_nonce, backup, join_id, token and msk from the saved cookie entry when rebuilding the request socket for a MP_JOIN 4th-ACK handled under SYN cookies, but it does not restore local_id, even though the SYN path saved it. subflow_ulp_clone() then reads that uninitialized field and stores it as the joined subflow's address-ID. Because the request-sock slab is SLAB_TYPESAFE_BY_RCU and not zeroed on allocation, the value is the stale byte of a previously freed request socket, which an off-path peer can influence by sending concurrent MP_JOIN SYNs. This corrupts the path manager's id-based subflow bookkeeping for the connection. Restore subflow_req->local_id from the cookie entry, as done for the other fields. Fixes: 9466a1ccebbe ("mptcp: enable JOIN requests even if cookies are in us= e") Cc: stable@vger.kernel.org Assisted-by: opencode:deepseek-v4-flash Signed-off-by: Harshit Varu --- net/mptcp/syncookies.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/mptcp/syncookies.c b/net/mptcp/syncookies.c index 7f2252634..b5cac5701 100644 --- a/net/mptcp/syncookies.c +++ b/net/mptcp/syncookies.c @@ -118,6 +118,7 @@ bool mptcp_token_join_cookie_init_state(struct mptcp_su= bflow_request_sock *subfl subflow_req->local_nonce =3D e->local_nonce; subflow_req->backup =3D e->backup; subflow_req->remote_id =3D e->join_id; + subflow_req->local_id =3D e->local_id; subflow_req->token =3D e->token; subflow_req->msk =3D msk; spin_unlock_bh(&join_entry_locks[i]); --=20 2.53.0