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mptcp: fix uninitialized local_id in syncookie MP_JOIN reconstruction

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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: 9466a1cceb ("mptcp: enable JOIN requests even if cookies are in use")
Cc: stable@vger.kernel.org
Signed-off-by: Harshit Varu <harshitvaru666@gmail.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260815115205.197151-1-harshitvaru666@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Harshit Varu 2026-08-15 17:22:05 +05:30 committed by Jakub Kicinski
parent 5e8076e4e4
commit b878dfdd12
1 changed files with 1 additions and 0 deletions
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net/mptcp/syncookies.c
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@ -118,6 +118,7 @@ bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subfl
subflow_req->local_nonce = e->local_nonce;
subflow_req->backup = e->backup;
subflow_req->remote_id = e->join_id;
subflow_req->local_id = e->local_id;
subflow_req->token = e->token;
subflow_req->msk = msk;
spin_unlock_bh(&join_entry_locks[i]);