From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 53003522694; Tue, 22 Sep 2026 08:54:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790067259; cv=none; b=rkK/krpt7364eAIZZdrk6CXWpm6gS8GQe3LsB5/mbchuhybsMDzGUVLSRmFegb99XtwnVbJx3iot5rqOH/rZsZU91LnLd0rVQyj2OE81gBPDx/NFoS1pPRzgnUPnTtTqvWdbu+44P81AeEOoal0eGA4kK9WdWrk3/IMiSHNM26o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790067259; c=relaxed/simple; bh=3ZTV/pSkrGqVG4UEI/jXaaswwIQyXULQcw5G9T2P+qo=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=OirPNi8lmSu5b/jMlDdToA8GfyONAgB6YESynUWoS9IwjOiROBzCEQY2HMzAD8IcupwKlZhP9Vcg7ULErn1a3NIHTewjtHXN+2hvLRgIgt7kdHu5ZjWiKYpia1DgGr0IGPG4otPpRAtmfN+JuNngFWrZ8Y9PqgQqtXVsVy6mEQ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nwG6gDHH; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nwG6gDHH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C7A301F00893; Tue, 22 Sep 2026 08:54:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790067257; bh=qC/KmragR2dwQD40DU3E5XJWqgNbvOuROd8+8Pl+HTo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=nwG6gDHH+ti+yT7knqXms9nW2o3/YrXl+r3fZOwTcsKWcms7I8N9GDI+Z4V3W/P8+ 4KmGiHh9ckOWXmY0KNfNILr8dP3ChWat1DS03orsIcr+W68ApyNCMe8sapb7NkNF3S MXllO9xpt/PFre8SEW+sIDjY1Sx87FD0A+kPfh+aVGptTDHuqVgOigu1Mm3Q4HHkpO W/4/XssLp74J+JMAPh2+wZF3yn298AO5Wd1QSmKiZmj7r3R1vBsAUJdJnQp4ozl1p0 fDvytuVAARwaLmkwqLvS1KNKpZgmHrmgMj8JkMfo7TM4DpBUywEd6f+E9LB9QSLmCT VLbUM1nj9bbNw== From: Allison Henderson To: netdev@vger.kernel.org, linux-rdma@vger.kernel.org, pabeni@redhat.com, edumazet@google.com, kuba@kernel.org, horms@kernel.org Cc: achender@kernel.org Subject: [PATCH net-next v6 10/12] net/rds: pin the connection across RDMA-CM event handling Date: Tue, 22 Sep 2026 01:54:08 -0700 Message-Id: <20260922085410.391323-11-achender@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260922085410.391323-1-achender@kernel.org> References: <20260922085410.391323-1-achender@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit rds_rdma_cm_event_handler_cmn() picks the connection up from cm_id->context, which carries no reference, and holds c_cm_lock - a mutex that lives in the connection's path array - across the transport callbacks. Before this series that was already a use-after-free whenever a callback destroyed the connection, since rds_conn_destroy() freed it synchronously and the handler's mutex_unlock() ran on freed memory; the one such callback, rds_ib_cm_connect_complete() on a protocol version below 3.1, has meanwhile been switched to rds_conn_drop() by commit f97d8c7bab78 ("rds: ib: use rds_conn_drop() on protocol version mismatch"), which also removed the deadlock that destroy took on c_cm_lock. Now that a connection is freed by its last reference, the remaining exposure is a callback that drops the last reference other than the handler's - which has none - and the reference handed out by rds_conn_create() to rds_ib_cm_handle_connect() and dropped at its end. Take a reference for the duration of the handler, and ignore the event if the connection is already being freed: its cm_id teardown is what stops event delivery, so an event that still arrives belongs to a connection whose shutdown has run and whose memory is on its way out. rds_ib_cm_handle_connect() has the mirror-image hole: a connection whose destroy has already quiesced it sits in RDS_CONN_DOWN with no cm_id, which is exactly the state the DOWN -> CONNECTING transition claims. A connect request arriving then would install a new cm_id and QP on a connection that is only waiting for its last reference to go away, and nothing would tear them down again. Re-check rds_destroy_pending() under c_cm_lock and reject the request instead. Assisted-by: Claude-Code:claude-fable-5 Signed-off-by: Allison Henderson --- net/rds/ib_cm.c | 11 +++++++++-- net/rds/rdma_transport.c | 16 +++++++++++++++- 2 files changed, 24 insertions(+), 3 deletions(-) diff --git a/net/rds/ib_cm.c b/net/rds/ib_cm.c index 786ddcb45bcb..1b5491598433 100644 --- a/net/rds/ib_cm.c +++ b/net/rds/ib_cm.c @@ -874,6 +874,13 @@ int rds_ib_cm_handle_connect(struct rdma_cm_id *cm_id, * see the comment above rds_queue_reconnect() */ mutex_lock(&conn->c_cm_lock); + /* A destroy that has already quiesced this conn leaves it in + * RDS_CONN_DOWN with no cm_id, exactly what the transition + * below would happily claim; nothing would tear the new cm_id + * and QP down again before the conn is freed. Reject instead. + */ + if (rds_destroy_pending(conn)) + goto out; if (!rds_conn_transition(conn, RDS_CONN_DOWN, RDS_CONN_CONNECTING)) { if (rds_conn_state(conn) == RDS_CONN_UP) { rdsdebug("incoming connect while connecting\n"); @@ -928,8 +935,8 @@ int rds_ib_cm_handle_connect(struct rdma_cm_id *cm_id, mutex_unlock(&conn->c_cm_lock); /* Drop the reference rds_conn_create() handed us. The * conn stays reachable through cm_id->context without a - * reference of its own for now; the CM event handler is - * given one of its own by a following patch. + * reference of its own; rds_rdma_cm_event_handler_cmn() + * takes one for the duration of each event it handles. */ rds_conn_put(conn); } diff --git a/net/rds/rdma_transport.c b/net/rds/rdma_transport.c index b15cf316b23a..584e9867810f 100644 --- a/net/rds/rdma_transport.c +++ b/net/rds/rdma_transport.c @@ -63,6 +63,18 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id, if (cm_id->device->node_type == RDMA_NODE_IB_CA) trans = &rds_ib_transport; + /* cm_id->context carries no reference of its own. Pin the + * connection for the duration of the handler: what the callbacks + * below do may drop the last reference other than ours, and the + * mutex released at out: lives in the connection's path array. + * A connection already being freed gets no events handled. + */ + if (conn && !rds_conn_get_unless_zero(conn)) { + rdsdebug("conn %p id %p is being freed, ignoring event\n", + conn, cm_id); + return 0; + } + /* Prevent shutdown from tearing down the connection * while we're executing. */ if (conn) { @@ -171,8 +183,10 @@ static int rds_rdma_cm_event_handler_cmn(struct rdma_cm_id *cm_id, } out: - if (conn) + if (conn) { mutex_unlock(&conn->c_cm_lock); + rds_conn_put(conn); + } rdsdebug("id %p event %u (%s) handling ret %d\n", cm_id, event->event, rdma_event_msg(event->event), ret); -- 2.25.1