CVE-2026-80983: net/smc: fix socket refcount leak in smc_switch_conns()

In the Linux kernel, the following vulnerability has been resolved:

net/smc: fix socket refcount leak in smcswitchconns()

smcswitchconns() takes a reference on the SMC socket before dropping lgr->connslock, so the connection stays alive while the CDC slot is fetched:

sockhold(&smc->sk); readunlockbh(&lgr->connslock); / pre-fetch buffer outside of sendlock, might sleep / rc = smccdcgetfreeslot(conn, tolnk, &wrbuf, NULL, &pend); if (rc) goto errout;

The errout label only drops the wrtx link reference, so this early exit returns without the matching sockput(). The second error exit is not affected, because sockput() has already run by then.

A leaked skrefcnt means the smcsock is never destroyed. Its send and receive buffers stay allocated, and for a user socket the reference held on the network namespace is never released, so the netns can no longer be torn down.

smccdcgetfreeslot() fails when the target link goes down or when the connection has been killed while the switch is in progress. Both are reachable during the link failover this function implements, so the leak is triggered by the same hardware events that make smcswitchconns() run in the first place.

Restructure so there is a single sockput() covering both outcomes, instead of adding a second one to the error path.