[PATCH 5.4 090/411] bpf: Fix excessive memory allocation in stack_map_alloc()

Greg Kroah-Hartman
2022-06-13T11:09:58Z

From: Yuntao Wang <ytcoode@gmail.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@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220407130423.798386-1-ytcoode@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/stackmap.c | 1 -
1 file changed, 1 deletion(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 49c7a09d688d..768ffd603787 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -117,7 +117,6 @@ 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