[PATCH net] net/smc: drop the abort_work reference when the work is cancelled

[Hidayath Khan <hidayath@linux.ibm.com>]

The schedulers of conn->abort_work hand a socket reference to the work
item and rely on it to give the reference back:

        sock_hold(&smc->sk); /* sock_put in abort_work */
        if (!queue_work(smc_close_wq, &conn->abort_work))
                sock_put(&smc->sk);

The queue_work() failure case is handled, but the cancellation case is
not. smc_conn_free() cancels a still-pending abort_work:

        if (current_work() != &conn->abort_work)
                cancel_work_sync(&conn->abort_work);

and discards the return value.  When cancel_work_sync() returns true the
work was queued but had not started, so smc_conn_abort_work() never runs
and its sock_put() never happens.  The reference is lost.

As in smc_switch_conns(), a leaked sk_refcnt means the smc_sock is never
destroyed: its buffers stay allocated and the network namespace reference
a user socket holds is never released, so the netns cannot be torn down.

smc_cdc_msg_validate() queues abort_work from the receive tasklet when a
peer sends a CDC message with an out-of-order sequence number, so a
remote peer combined with a concurrent local close is enough to reach it.

Drop the reference when the work is cancelled, matching the pattern
smc_close_cancel_work() already uses for conn->close_work:

        if (cancel_work_sync(&smc->conn.close_work))
                sock_put(sk);

The sock_put() is safe here: every caller of smc_conn_free() passes the
connection of a socket it holds a reference to, so this cannot release
the last one.

Fixes: b286a0651e44 ("net/smc: handle incoming CDC validation message")
Cc: stable@vger.kernel.org
Reviewed-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>
Signed-off-by: Hidayath Khan <hidayath@linux.ibm.com>
---
 net/smc/smc_core.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index c0027d2fe4e8..dd9fffbe41e0 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -1254,6 +1254,7 @@ static void smc_buf_unuse(struct smc_connection *conn,
 /* remove a finished connection from its link group */
 void smc_conn_free(struct smc_connection *conn)
 {
+	struct smc_sock *smc = container_of(conn, struct smc_sock, conn);
 	struct smc_link_group *lgr = conn->lgr;
 
 	if (!lgr || conn->freed)
@@ -1277,8 +1278,13 @@ void smc_conn_free(struct smc_connection *conn)
 		tasklet_kill(&conn->rx_tsklet);
 	} else {
 		smc_cdc_wait_pend_tx_wr(conn);
-		if (current_work() != &conn->abort_work)
-			cancel_work_sync(&conn->abort_work);
+		/* If the work was pending (cancel returns true) it never ran,
+		 * so the sock_hold taken by its scheduler was never released.
+		 */
+		if (current_work() != &conn->abort_work) {
+			if (cancel_work_sync(&conn->abort_work))
+				sock_put(&smc->sk);
+		}
 	}
 	if (!list_empty(&lgr->list)) {
 		smc_buf_unuse(conn, lgr); /* allow buffer reuse */

base-commit: 2b1c2bc2355fd59cc75045e42d9dc5470ef5fa9a
-- 
2.52.0