[PATCH 5.15 64/66] bpf: Fix excessive memory allocation in stack_map_alloc()

[Greg Kroah-Hartman]

From: Yuntao Wang <ytcoode@xxxxxxxxx>

commit b45043192b3e481304062938a6561da2ceea46a6 upstream.

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@xxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20220407130423.798386-1-ytcoode@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/bpf/stackmap.c |    1 -
 1 file changed, 1 deletion(-)

--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -119,7 +119,6 @@ static struct bpf_map *stack_map_alloc(u
 		return ERR_PTR(-E2BIG);
 
 	cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
-	cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));
 	smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr));
 	if (!smap)
 		return ERR_PTR(-ENOMEM);