net/smc: fix qentry overwrite for CONFIRM_LINK and ADD_LINK_CONT in smc_llc_event_han...

net/smc: fix qentry overwrite for CONFIRM_LINK and ADD_LINK_CONT in smc_llc_event_handler()

The SMC_LLC_CONFIRM_LINK / SMC_LLC_ADD_LINK_CONT branch in
smc_llc_event_handler() stores an incoming qentry into the local LLC flow
without first checking whether a qentry is already pending. If a malicious or
buggy peer sends a second CONFIRM_LINK or ADD_LINK_CONT request while a flow is
active and flow->qentry is already set, smc_llc_flow_qentry_set() overwrites the
pointer without freeing the previous allocation, leaking one kmalloc-96 object
per spurious message.

The sibling SMC_LLC_DELETE_LINK branch already has the correct !flow->qentry
guard. Apply the same guard to the CONFIRM_LINK/ADD_LINK_CONT branch so that a
duplicate message when qentry is already occupied falls through to break and is
freed by the kfree(qentry) at the out: label, rather than silently leaking the
existing allocation.

The response direction (smc_llc_rx_response()) is unaffected: it already guards
with flow->qentry at the equivalent site and drops duplicate responses
correctly.

Fixes: 0fb0b02bd6fd ("net/smc: adapt SMC client code to use the LLC flow")
Signed-off-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Reviewed-by: Hidayath Khan <hidayath@linux.ibm.com>
Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Link: https://patch.msgid.link/20260729130153.970800-1-mjambigi@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>