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

[高逸飞]

Hi Hidayath,

Thanks for the fix — I see yours covers the same issue and was posted
first. Please disregard my duplicate.


Hidayathulla Khan I <hidayath@xxxxxxxxxxxxx> 于2026年8月5日周三 02:26写道：
>
> Hi Yifei,
>
> Thanks for looking into this.
>
> Yes I have submitted a patch for the same issue.
> https://lore.kernel.org/netdev/20260804082800.498672-1-hidayath@xxxxxxxxxxxxx/
>
> Hidayath
>
> On 05/08/26 3:09 am, Yifei Gao wrote:
> > 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@xxxxxxxxxxxxxxx
> > Assisted-by: Claude:claude-opus-4-8
> > Signed-off-by: Yifei Gao <gyf161023@xxxxxxxxx>
> > ---
> >   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);