lib: cpu_rmap: Fix potential use-after-free in irq_cpu_rmap_release()

irq_cpu_rmap_release() calls cpu_rmap_put(), which may free the rmap.
So we need to clear the pointer to our glue structure in rmap before
doing that, not after.

Fixes: 4e0473f ("lib: cpu_rmap: Avoid use after free on rmap->obj array entries")
Signed-off-by: Ben Hutchings <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: bwhacks

lib/cpu_rmap.c

@@ -280,8 +280,8 @@ static void irq_cpu_rmap_release(struct kref *ref)
 	struct irq_glue *glue =
 		container_of(ref, struct irq_glue, notify.kref);
 
-	cpu_rmap_put(glue->rmap);
 	glue->rmap->obj[glue->index] = NULL;
+	cpu_rmap_put(glue->rmap);
 	kfree(glue);
 }