drbd: fifo_alloc() should use struct_size

Switching to struct_size for the allocation in fifo_alloc avoids
hard-coding the type of fifo_buffer.values in fifo_alloc. It also
provides overflow protection; to avoid pessimistic code being
generated by the compiler as a result, this patch also switches
fifo_size to unsigned, propagating the change as appropriate.
Reviewed-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/drbd/drbd_int.h

@@ -622,7 +622,7 @@ struct fifo_buffer {
 	int total; /* sum of all values */
 	int values[0];
 };
-extern struct fifo_buffer *fifo_alloc(int fifo_size);
+extern struct fifo_buffer *fifo_alloc(unsigned int fifo_size);
 
 /* flag bits per connection */
 enum {

drivers/block/drbd/drbd_nl.c

@@ -1575,7 +1575,8 @@ int drbd_adm_disk_opts(struct sk_buff *skb, struct genl_info *info)
 	struct drbd_device *device;
 	struct disk_conf *new_disk_conf, *old_disk_conf;
 	struct fifo_buffer *old_plan = NULL, *new_plan = NULL;
-	int err, fifo_size;
+	int err;
+	unsigned int fifo_size;
 
 	retcode = drbd_adm_prepare(&adm_ctx, skb, info, DRBD_ADM_NEED_MINOR);
 	if (!adm_ctx.reply_skb)

drivers/block/drbd/drbd_receiver.c

@@ -3887,7 +3887,7 @@ static int receive_SyncParam(struct drbd_connection *connection, struct packet_i
 	struct disk_conf *old_disk_conf = NULL, *new_disk_conf = NULL;
 	const int apv = connection->agreed_pro_version;
 	struct fifo_buffer *old_plan = NULL, *new_plan = NULL;
-	int fifo_size = 0;
+	unsigned int fifo_size = 0;
 	int err;
 
 	peer_device = conn_peer_device(connection, pi->vnr);

drivers/block/drbd/drbd_worker.c

@@ -482,11 +482,11 @@ static void fifo_add_val(struct fifo_buffer *fb, int value)
 		fb->values[i] += value;
 }
 
-struct fifo_buffer *fifo_alloc(int fifo_size)
+struct fifo_buffer *fifo_alloc(unsigned int fifo_size)
 {
 	struct fifo_buffer *fb;
 
-	fb = kzalloc(sizeof(struct fifo_buffer) + sizeof(int) * fifo_size, GFP_NOIO);
+	fb = kzalloc(struct_size(fb, values, fifo_size), GFP_NOIO);
 	if (!fb)
 		return NULL;