linux-kernel - [PATCH bpf-next v4 2/4] bpf: Free special fields when update hash maps with BPF_F

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Message-ID: <20251030152451.62778-3-leon.hwang@linux.dev>
Date: Thu, 30 Oct 2025 23:24:49 +0800
From: Leon Hwang <leon.hwang@...ux.dev>
To: bpf@...r.kernel.org
Cc: ast@...nel.org,
	andrii@...nel.org,
	daniel@...earbox.net,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	john.fastabend@...il.com,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	memxor@...il.com,
	ameryhung@...il.com,
	linux-kernel@...r.kernel.org,
	kernel-patches-bot@...com,
	Leon Hwang <leon.hwang@...ux.dev>
Subject: [PATCH bpf-next v4 2/4] bpf: Free special fields when update hash maps with BPF_F_LOCK

When updating hash maps with BPF_F_LOCK, 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.

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

Fixes: 14a324f6a67e ("bpf: Wire up freeing of referenced kptr")
Signed-off-by: Leon Hwang <leon.hwang@...ux.dev>
---
 kernel/bpf/hashtab.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 3861f28a6be81..fc3c7ede3cd0c 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1110,6 +1110,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 			copy_map_value_locked(map,
 					      htab_elem_value(l_old, key_size),
 					      value, false);
+			check_and_free_fields(htab, l_old);
 			return 0;
 		}
 		/* fall through, grab the bucket lock and lookup again.
@@ -1138,6 +1139,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 		copy_map_value_locked(map,
 				      htab_elem_value(l_old, key_size),
 				      value, false);
+		check_and_free_fields(htab, l_old);
 		ret = 0;
 		goto err;
 	}
-- 
2.51.1