[PATCH rdma-next 6/8] RDMA/core: Fix potential use after free in ib_free_cq()

[Edward Srouji]

From: Patrisious Haddad <phaddad@xxxxxxxxxx>

When accessing a CQ via the netlink path the only synchronization
mechanism for the said CQ is rdma_restrack_get().
Currently, rdma_restrack_del() is invoked at the end of
ib_free_cq(), which is too late, since by that point
vendor-specific resources associated with the CQ might already be
freed. This can leave a short window where the CQ remains accessible
through restrack, leading to a potential use-after-free.

Fix this by moving the rdma_restrack_del() call to be before the freeing
of the vendor-specific resources ensuring that the CQ is removed from
restrack before its internal resources are released.
This guarantees that no new users hold references to a CQ that is in
the process of destruction.

Fixes: 43d781b9fa56 ("RDMA: Allow fail of destroy CQ")
Signed-off-by: Patrisious Haddad <phaddad@xxxxxxxxxx>
Reviewed-by: Michael Guralnik <michaelgur@xxxxxxxxxx>
Signed-off-by: Edward Srouji <edwards@xxxxxxxxxx>
---
 drivers/infiniband/core/cq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/infiniband/core/cq.c b/drivers/infiniband/core/cq.c
index 3d7b6cddd131c4ed07082719fc9e3b4bfdb51459..1379808e1404096654e8dc73a11f90d939910e54 100644
--- a/drivers/infiniband/core/cq.c
+++ b/drivers/infiniband/core/cq.c
@@ -327,6 +327,7 @@ void ib_free_cq(struct ib_cq *cq)
 	if (WARN_ON_ONCE(cq->cqe_used))
 		return;
 
+	rdma_restrack_del(&cq->res);
 	if (cq->device->ops.pre_destroy_cq) {
 		ret = cq->device->ops.pre_destroy_cq(cq);
 		WARN_ONCE(ret, "Disable of kernel CQ shouldn't fail");
@@ -353,7 +354,6 @@ void ib_free_cq(struct ib_cq *cq)
 	else
 		ret = cq->device->ops.destroy_cq(cq, NULL);
 	WARN_ONCE(ret, "Destroy of kernel CQ shouldn't fail");
-	rdma_restrack_del(&cq->res);
 	kfree(cq->wc);
 	kfree(cq);
 }

-- 
2.49.0