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

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Message-ID: <20251106205852.45511-1-a.safin@rosa.ru>
Date: Thu,  6 Nov 2025 23:58:44 +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] 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.

Cast value_size to u64 before multiplying.

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

Fixes: 304849a27b34 ("bpf: hashtab memory usage")
Cc: stable@...r.kernel.org
Signed-off-by: Alexei Safin <a.safin@...a.ru>
---
 kernel/bpf/hashtab.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 570e2f723144..7ad6b5137ba1 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -2269,7 +2269,7 @@ static u64 htab_map_mem_usage(const struct bpf_map *map)
 		usage += htab->elem_size * num_entries;
 
 		if (percpu)
-			usage += value_size * num_possible_cpus() * num_entries;
+			usage += (u64)value_size * num_possible_cpus() * num_entries;
 		else if (!lru)
 			usage += sizeof(struct htab_elem *) * num_possible_cpus();
 	} else {
@@ -2281,7 +2281,7 @@ static u64 htab_map_mem_usage(const struct bpf_map *map)
 		usage += (htab->elem_size + LLIST_NODE_SZ) * num_entries;
 		if (percpu) {
 			usage += (LLIST_NODE_SZ + sizeof(void *)) * num_entries;
-			usage += value_size * num_possible_cpus() * num_entries;
+			usage += (u64)value_size * num_possible_cpus() * num_entries;
 		}
 	}
 	return usage;
-- 
2.50.1 (Apple Git-155)