bpf: Fix incorrect memory charge cost calculation in stack_map_alloc()

commit b450431 upstream.

This is a backport of the original upstream patch for 5.4/5.10.

The original upstream patch has been applied to 5.4/5.10 branches, which
simply removed the line:

  cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));

This is correct for upstream branch but incorrect for 5.4/5.10 branches,
as the 5.4/5.10 branches do not have the commit 3708681 ("bpf:
Eliminate rlimit-based memory accounting for stackmap maps"), so the
bpf_map_charge_init() function has not been removed.

Currently the bpf_map_charge_init() function in 5.4/5.10 branches takes a
wrong memory charge cost, the

  attr->max_entries * (sizeof(struct stack_map_bucket) + (u64)value_size))

part is missing, let's fix it.

Cc: <stable@vger.kernel.org> # 5.4.y
Cc: <stable@vger.kernel.org> # 5.10.y
Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/bpf/stackmap.c

@@ -121,7 +121,8 @@ 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);
-	err = bpf_map_charge_init(&mem, cost);
+	err = bpf_map_charge_init(&mem, cost + attr->max_entries *
+			   (sizeof(struct stack_map_bucket) + (u64)value_size));
 	if (err)
 		return ERR_PTR(err);