[PATCH] net/smc: fix sock refcount leak in smc_switch_conns() error path

[Yifei Gao <gyf161023@gmail.com>]

smc_switch_conns() takes a reference on the socket with sock_hold() before
dropping conns_lock to prefetch a tx slot. On success the reference is
released by the sock_put() after smc_switch_cursor(). When
smc_cdc_get_free_slot() fails, however, the function jumps straight to
err_out without a sock_put(), leaking the reference and leaving the socket
unreclaimable. During SMC-R link failover with an exhausted backup link
this leaks one reference per failing connection switch.

Release the reference before jumping to err_out. The err_out label is also
reached from the smc_switch_cursor() failure path, which has already done
its own sock_put(), so the put must stay at the get_free_slot failure site
rather than at the label.

Fixes: c6f02ebeea3a ("net/smc: switch connections to alternate link")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Yifei Gao <gyf161023@gmail.com>
---
 net/smc/smc_core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index cf6b620fef05..04c6ce608ec7 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -1148,8 +1148,10 @@ struct smc_link *smc_switch_conns(struct smc_link_group *lgr,
 		read_unlock_bh(&lgr->conns_lock);
 		/* pre-fetch buffer outside of send_lock, might sleep */
 		rc = smc_cdc_get_free_slot(conn, to_lnk, &wr_buf, NULL, &pend);
-		if (rc)
+		if (rc) {
+			sock_put(&smc->sk);
 			goto err_out;
+		}
 		/* avoid race with smcr_tx_sndbuf_nonempty() */
 		spin_lock_bh(&conn->send_lock);
 		smc_switch_link_and_count(conn, to_lnk);
-- 
2.43.0