[PATCH net] net/smc: free stashed qentry before overwrite in REQ_ADD_LINK to ADD_LINK transition

[PATCH net] net/smc: free stashed qentry before overwrite in REQ_ADD_LINK to ADD_LINK transition

[Mahanta Jambigi]

When smc_llc_event_handler() transitions the local LLC flow from
SMC_LLC_FLOW_REQ_ADD_LINK to SMC_LLC_FLOW_ADD_LINK on arrival of an ADD_LINK
request, it calls smc_llc_flow_qentry_set() unconditionally:

	if (lgr->llc_flow_lcl.type == SMC_LLC_FLOW_REQ_ADD_LINK) {
		lgr->llc_flow_lcl.type = SMC_LLC_FLOW_ADD_LINK;
		smc_llc_flow_qentry_set(&lgr->llc_flow_lcl, qentry);
		...
	}

A CONFIRM_LINK or ADD_LINK_CONT arriving while flow->type is
SMC_LLC_FLOW_REQ_ADD_LINK is stashed into flow->qentry via the
SMC_LLC_CONFIRM_LINK / SMC_LLC_ADD_LINK_CONT handler (which stores into
flow->qentry for any non-NONE flow type).  When the subsequent ADD_LINK
arrives, the REQ_ADD_LINK branch overwrites flow->qentry with the new pointer
without first freeing the stashed allocation, leaking one kmalloc object.

The stashed entry has no consumer: smc_llc_wait() is only called from
llc_add_link_work, which is not yet scheduled while the flow type remains
REQ_ADD_LINK.  No waiter is sleeping on llc_msg_waiter at this point.
It is safe to unconditionally free any stashed qentry before
the overwrite.

Call smc_llc_flow_qentry_del() before smc_llc_flow_qentry_set() in the
REQ_ADD_LINK branch.  smc_llc_flow_qentry_del() already checks flow->qentry
before freeing, so the normal path where no entry is stashed is a no-op.

Fixes: b4ba4652b3f8 ("net/smc: extend LLC layer for SMC-Rv2")
Reviewed-by: Hidayath Khan <hidayath@linux.ibm.com>
Signed-off-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
---
 net/smc/smc_llc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/smc/smc_llc.c b/net/smc/smc_llc.c
index 07e2d7fef7b2..9cc4b3e97699 100644
--- a/net/smc/smc_llc.c
+++ b/net/smc/smc_llc.c
@@ -1911,6 +1911,8 @@ static void smc_llc_event_handler(struct smc_llc_qentry *qentry)
 			if (lgr->llc_flow_lcl.type ==
 					SMC_LLC_FLOW_REQ_ADD_LINK) {
 				/* server started add_link processing */
+				/* free any qentry stashed in REQ_ADD_LINK state */
+				smc_llc_flow_qentry_del(&lgr->llc_flow_lcl);
 				lgr->llc_flow_lcl.type = SMC_LLC_FLOW_ADD_LINK;
 				smc_llc_flow_qentry_set(&lgr->llc_flow_lcl,
 							qentry);
-- 
2.50.1