[PATCH][next] hostap: Add __counted_by for struct prism2_download_data and use struct_size()

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

While there, use struct_size() helper, instead of the open-coded
version, to calculate the size for the allocation of the whole
flexible structure, including of course, the flexible-array member.

This code was found with the help of Coccinelle, and audited and
fixed manually.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/net/wireless/intersil/hostap/hostap_download.c | 3 +--
 drivers/net/wireless/intersil/hostap/hostap_wlan.h     | 2 +-
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/intersil/hostap/hostap_download.c b/drivers/net/wireless/intersil/hostap/hostap_download.c
index 3672291ced5c..5e5bada28b5b 100644
--- a/drivers/net/wireless/intersil/hostap/hostap_download.c
+++ b/drivers/net/wireless/intersil/hostap/hostap_download.c
@@ -732,8 +732,7 @@ static int prism2_download(local_info_t *local,
 		goto out;
 	}
 
-	dl = kzalloc(sizeof(*dl) + param->num_areas *
-		     sizeof(struct prism2_download_data_area), GFP_KERNEL);
+	dl = kzalloc(struct_size(dl, data, param->num_areas), GFP_KERNEL);
 	if (dl == NULL) {
 		ret = -ENOMEM;
 		goto out;
diff --git a/drivers/net/wireless/intersil/hostap/hostap_wlan.h b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
index c25cd21d18bd..f71c0545c0be 100644
--- a/drivers/net/wireless/intersil/hostap/hostap_wlan.h
+++ b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
@@ -617,7 +617,7 @@ struct prism2_download_data {
 		u32 addr; /* wlan card address */
 		u32 len;
 		u8 *data; /* allocated data */
-	} data[];
+	} data[] __counted_by(num_areas);
 };
 
 
-- 
2.34.1