[PATCH bpf-next] bpf: Reduce smap->elem_size

[Martin KaFai Lau <martin.lau@linux.dev>]

From: Martin KaFai Lau <martin.lau@kernel.org>

'struct bpf_local_storage_elem' has a 56 bytes padding at the end
which can be used for attr->value_size.  The current smap->elem_size
calculation is unnecessarily inflated by 56 bytes.

The patch is to fix it by calculating the smap->elem_size
with offsetof().

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
 kernel/bpf/bpf_local_storage.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index b39a46e8fb08..cb43e70613b1 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -580,8 +580,8 @@ static struct bpf_local_storage_map *__bpf_local_storage_map_alloc(union bpf_att
 		raw_spin_lock_init(&smap->buckets[i].lock);
 	}
 
-	smap->elem_size =
-		sizeof(struct bpf_local_storage_elem) + attr->value_size;
+	smap->elem_size = offsetof(struct bpf_local_storage_elem, sdata) +
+		offsetof(struct bpf_local_storage_data, data[attr->value_size]);
 
 	return smap;
 }
-- 
2.30.2