5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Harshit Varu <redacted>
commit b878dfdd12d7a5b8722a78d35e313506140ca3d9 upstream.
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 use")
Cc: <redacted>
Signed-off-by: Harshit Varu <redacted>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260815115205.197151-1-harshitvaru666@gmail.com (local)
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/mptcp/syncookies.c | 1 +
1 file changed, 1 insertion(+)
--- a/net/mptcp/syncookies.c
+++ b/net/mptcp/syncookies.c
@@ -118,6 +118,7 @@ bool mptcp_token_join_cookie_init_state(
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]);