[PATCH bpf v3 3/4] bpf: Free special fields when update local storage maps

[Leon Hwang <leon.hwang@linux.dev>]

When updating local storage maps with BPF_F_LOCK on the fast path, the
special fields were not freed after being replaced. This could cause
memory referenced by BPF_KPTR_{REF,PERCPU} fields to be held until the
map gets freed.

Similarly, on the other path, the old sdata's special fields were never
freed regardless of whether BPF_F_LOCK was used, causing the same issue.

Fix this by calling 'bpf_obj_free_fields()' after
'copy_map_value_locked()' to properly release the old fields.

Fixes: 9db44fdd8105 ("bpf: Support kptrs in local storage maps")
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 kernel/bpf/bpf_local_storage.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index b931fbceb54da..8e3aea4e07c50 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -609,6 +609,7 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 		if (old_sdata && selem_linked_to_storage_lockless(SELEM(old_sdata))) {
 			copy_map_value_locked(&smap->map, old_sdata->data,
 					      value, false);
+			bpf_obj_free_fields(smap->map.record, old_sdata->data);
 			return old_sdata;
 		}
 	}
@@ -641,6 +642,7 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 	if (old_sdata && (map_flags & BPF_F_LOCK)) {
 		copy_map_value_locked(&smap->map, old_sdata->data, value,
 				      false);
+		bpf_obj_free_fields(smap->map.record, old_sdata->data);
 		selem = SELEM(old_sdata);
 		goto unlock;
 	}
@@ -654,6 +656,7 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 
 	/* Third, remove old selem, SELEM(old_sdata) */
 	if (old_sdata) {
+		bpf_obj_free_fields(smap->map.record, old_sdata->data);
 		bpf_selem_unlink_map(SELEM(old_sdata));
 		bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
 						true, &old_selem_free_list);
-- 
2.51.0