[PATCH] RDMA/siw: Fix use-after-free in siw_accept()

[Shuangpeng Bai <shuangpeng.kernel@gmail.com>]

siw_accept() looks up the QP supplied by userspace. If that QP is
already in RTS, the function jumps to error cleanup before associating
the incoming CEP with it.

The cleanup tests whether qp->cep is non-NULL and assumes the current
call installed the association. However, qp->cep can point to the CEP
of an existing connection. The cleanup then drops a reference from the
incoming cep, not qp->cep. Once the incoming endpoint loses its
remaining references, this can free it before the subsequent cep->qp
store, causing a use-after-free. It also clears the existing QP
association.

Only release the association reference when qp->cep is the incoming
CEP. This preserves an existing association and avoids accessing the
freed endpoint.

Fixes: 6c52fdc244b5 ("rdma/siw: connection management")
Cc: stable@vger.kernel.org
Signed-off-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>
---
 drivers/infiniband/sw/siw/siw_cm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/infiniband/sw/siw/siw_cm.c b/drivers/infiniband/sw/siw/siw_cm.c
index 87c79527ac09..0245b25e7271 100644
--- a/drivers/infiniband/sw/siw/siw_cm.c
+++ b/drivers/infiniband/sw/siw/siw_cm.c
@@ -1751,7 +1751,7 @@ int siw_accept(struct iw_cm_id *id, struct iw_cm_conn_param *params)
 	cep->state = SIW_EPSTATE_CLOSED;
 
 	siw_free_cm_id(cep);
-	if (qp->cep) {
+	if (qp->cep == cep) {
 		siw_cep_put(cep);
 		qp->cep = NULL;
 	}
-- 
2.43.0