[PATCH rdma-next v2 05/11] RDMA/core: Fix potential use after free in ib_destroy_cq_user()

[Edward Srouji <edwards@nvidia.com>]

From: Patrisious Haddad <phaddad@nvidia.com>

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_destroy_cq_user(), 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 the start of
ib_destroy_cq_user(), 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.

In addition, this change preserves the intended asymmetric behavior
between create and destroy routines: resources are added to the
restrack at the end of successful creation, and hence shall be removed
from the restrack first thing during the destruction flow, which keeps
the lifecycle management consistent and predictable.

Fixes: 08f294a1524b ("RDMA/core: Add resource tracking for create and destroy CQs")
Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Reviewed-by: Michael Guralnik <michaelgur@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
---
 drivers/infiniband/core/verbs.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/verbs.c b/drivers/infiniband/core/verbs.c
index f1438d5802a3e97e22cdb607cf90a097d041a162..0e8f99807c7c0ce063ed0c1561f4ba42b485b69d 100644
--- a/drivers/infiniband/core/verbs.c
+++ b/drivers/infiniband/core/verbs.c
@@ -2256,12 +2256,16 @@ int ib_destroy_cq_user(struct ib_cq *cq, struct ib_udata *udata)
 	if (atomic_read(&cq->usecnt))
 		return -EBUSY;
 
+	rdma_restrack_del(&cq->res);
+
 	ret = cq->device->ops.destroy_cq(cq, udata);
-	if (ret)
+	if (ret) {
+		rdma_restrack_new(&cq->res, RDMA_RESTRACK_CQ);
+		rdma_restrack_add(&cq->res);
 		return ret;
+	}
 
 	ib_umem_release(cq->umem);
-	rdma_restrack_del(&cq->res);
 	kfree(cq);
 	return ret;
 }

-- 
2.49.0