bpf: Free special fields when update [lru_,]percpu_hash maps

As [lru_,]percpu_hash maps support BPF_KPTR_{REF,PERCPU}, missing
calls to 'bpf_obj_free_fields()' in 'pcpu_copy_value()' could cause the
memory referenced by BPF_KPTR_{REF,PERCPU} fields to be held until the
map gets freed.

Fix this by calling 'bpf_obj_free_fields()' after
'copy_map_value[,_long]()' in 'pcpu_copy_value()'.

Fixes: 65334e6 ("bpf: Support kptrs in percpu hashmap and percpu LRU hashmap")
Signed-off-by: Leon Hwang <[email protected]>

Author: Asphaltt

kernel/bpf/hashtab.c

@@ -934,15 +934,21 @@ static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
 static void pcpu_copy_value(struct bpf_htab *htab, void __percpu *pptr,
 			    void *value, bool onallcpus)
 {
+	void *ptr;
+
 	if (!onallcpus) {
 		/* copy true value_size bytes */
-		copy_map_value(&htab->map, this_cpu_ptr(pptr), value);
+		ptr = this_cpu_ptr(pptr);
+		copy_map_value(&htab->map, ptr, value);
+		bpf_obj_free_fields(htab->map.record, ptr);
 	} else {
 		u32 size = round_up(htab->map.value_size, 8);
 		int off = 0, cpu;
 
 		for_each_possible_cpu(cpu) {
-			copy_map_value_long(&htab->map, per_cpu_ptr(pptr, cpu), value + off);
+			ptr = per_cpu_ptr(pptr, cpu);
+			copy_map_value_long(&htab->map, ptr, value + off);
+			bpf_obj_free_fields(htab->map.record, ptr);
 			off += size;
 		}
 	}