[PATCH rdma-next 5/8] RDMA/core: Fix potential use after free in counter_release()

[Edward Srouji <edwards@nvidia.com>]

From: Patrisious Haddad <phaddad@nvidia.com>

When accessing a counter via the netlink path the only synchronization
mechanism for the said counter is rdma_restrack_get().
Currently, rdma_restrack_del() is invoked at the end of
counter_release(), which is too late, since by that point
vendor-specific resources associated with the counter might already be
freed. This can leave a short window where the counter 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 counter is
removed from restrack before its internal resources are released.
This guarantees that no new users hold references to a counter that is
in the process of destruction.

Fixes: 99fa331dc862 ("RDMA/counter: Add "auto" configuration mode support")
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/counters.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/counters.c b/drivers/infiniband/core/counters.c
index a9e189194c1300a37479502959ddc1d1687bd40e..a2c85840c501a74752973bcb31452da9aa2e84fa 100644
--- a/drivers/infiniband/core/counters.c
+++ b/drivers/infiniband/core/counters.c
@@ -234,7 +234,6 @@ static void rdma_counter_free(struct rdma_counter *counter)
 
 	mutex_unlock(&port_counter->lock);
 
-	rdma_restrack_del(&counter->res);
 	rdma_free_hw_stats_struct(counter->stats);
 	kfree(counter);
 }
@@ -329,6 +328,7 @@ static void counter_release(struct kref *kref)
 
 	counter = container_of(kref, struct rdma_counter, kref);
 	counter_history_stat_update(counter);
+	rdma_restrack_del(&counter->res);
 	counter->device->ops.counter_dealloc(counter);
 	rdma_counter_free(counter);
 }
@@ -490,7 +490,8 @@ static struct rdma_counter *rdma_get_counter_by_id(struct ib_device *dev,
 		return NULL;
 
 	counter = container_of(res, struct rdma_counter, res);
-	kref_get(&counter->kref);
+	if (!kref_get_unless_zero(&counter->kref))
+		counter = NULL;
 	rdma_restrack_put(res);
 
 	return counter;

-- 
2.49.0