linux-kernel - [PATCH 5.10 136/452] bpf: Fix excessive memory allocation in stack_map

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Message-Id: <20220607164912.613808833@linuxfoundation.org>
Date:   Tue,  7 Jun 2022 18:59:53 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yuntao Wang <ytcoode@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 136/452] bpf: Fix excessive memory allocation in stack_map_alloc()

From: Yuntao Wang <ytcoode@...il.com>

[ Upstream commit b45043192b3e481304062938a6561da2ceea46a6 ]

The 'n_buckets * (value_size + sizeof(struct stack_map_bucket))' part of the
allocated memory for 'smap' is never used after the memlock accounting was
removed, thus get rid of it.

[ Note, Daniel:

Commit b936ca643ade ("bpf: rework memlock-based memory accounting for maps")
moved `cost += n_buckets * (value_size + sizeof(struct stack_map_bucket))`
up and therefore before the bpf_map_area_alloc() allocation, sigh. In a later
step commit c85d69135a91 ("bpf: move memory size checks to bpf_map_charge_init()"),
and the overflow checks of `cost >= U32_MAX - PAGE_SIZE` moved into
bpf_map_charge_init(). And then 370868107bf6 ("bpf: Eliminate rlimit-based
memory accounting for stackmap maps") finally removed the bpf_map_charge_init().
Anyway, the original code did the allocation same way as /after/ this fix. ]

Fixes: b936ca643ade ("bpf: rework memlock-based memory accounting for maps")
Signed-off-by: Yuntao Wang <ytcoode@...il.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Link: https://lore.kernel.org/bpf/20220407130423.798386-1-ytcoode@gmail.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/bpf/stackmap.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 4575d2d60cb1..c19e669afba0 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -121,7 +121,6 @@ static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
 		return ERR_PTR(-E2BIG);

 	cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
-	cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));
 	err = bpf_map_charge_init(&mem, cost);
 	if (err)
 		return ERR_PTR(err);
-- 
2.35.1