linux-kernel - [PATCH v2] bpf: hashtab: fix 32-bit overflow in memory usage calculation

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Message-ID: <20251107100310.61478-1-a.safin@rosa.ru>
Date: Fri,  7 Nov 2025 13:03:05 +0300
From: Alexei Safin <a.safin@...a.ru>
To: Alexei Starovoitov <ast@...nel.org>
Cc: Alexei Safin <a.safin@...a.ru>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Yafang Shao <laoar.shao@...il.com>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lvc-patches@...uxtesting.org,
	stable@...r.kernel.org
Subject: [PATCH v2] bpf: hashtab: fix 32-bit overflow in memory usage calculation

The intermediate product value_size * num_possible_cpus() is evaluated
in 32-bit arithmetic and only then promoted to 64 bits. On systems with
large value_size and many possible CPUs this can overflow and lead to
an underestimated memory usage.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 304849a27b34 ("bpf: hashtab memory usage")
Cc: stable@...r.kernel.org
Suggested-by: Yafang Shao <laoar.shao@...il.com>
Signed-off-by: Alexei Safin <a.safin@...a.ru>
---
v2: Promote value_size to u64 at declaration to avoid 32-bit overflow
in all arithmetic using this variable (suggested by Yafang Shao)
 kernel/bpf/hashtab.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 570e2f723144..1f0add26ba3f 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -2252,7 +2252,7 @@ static long bpf_for_each_hash_elem(struct bpf_map *map, bpf_callback_t callback_
 static u64 htab_map_mem_usage(const struct bpf_map *map)
 {
 	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
-	u32 value_size = round_up(htab->map.value_size, 8);
+	u64 value_size = round_up(htab->map.value_size, 8);
 	bool prealloc = htab_is_prealloc(htab);
 	bool percpu = htab_is_percpu(htab);
 	bool lru = htab_is_lru(htab);
-- 
2.50.1 (Apple Git-155)