[PATCH rdma-next 5/6] 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_begin_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
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 8bd39cfcf41bce3a20cfbc41be6f51a1f7f95a8a..bca0e48f6805e87554e77139ce6812d6b7236802 100644
--- a/drivers/infiniband/core/verbs.c
+++ b/drivers/infiniband/core/verbs.c
@@ -2250,11 +2250,15 @@ int ib_destroy_cq_user(struct ib_cq *cq, struct ib_udata *udata)
 	if (atomic_read(&cq->usecnt))
 		return -EBUSY;
 
+	rdma_restrack_begin_del(&cq->res);
+
 	ret = cq->device->ops.destroy_cq(cq, udata);
-	if (ret)
+	if (ret) {
+		rdma_restrack_abort_del(&cq->res);
 		return ret;
+	}
 
-	rdma_restrack_del(&cq->res);
+	rdma_restrack_commit_del(&cq->res);
 	kfree(cq);
 	return ret;
 }

-- 
2.49.0