mwifiex: fix tx_info/rx_info overlap with PCIe dma_mapping

On PCIe Tx data path, network interface specific tx_info
parameters such as bss_num and bss_type are saved at
"skb->cb + sizeof(dma_addr_t)" (returned by MWIFIEX_SKB_TXCB).
Later mwifiex_map_pci_memory() called from
mwifiex_pcie_send_data() will memcpy
sizeof(struct mwifiex_dma_mapping) bytes to save PCIe DMA
address and length information at beginning of skb->cb.
This accidently overwrites bss_num and bss_type saved in skb->cb
previously because bss_num/bss_type and mwifiex_dma_mapping data
overlap.
Similarly, on PCIe Rx data path, rx_info parameters overlaps
with PCIe DMA address and length information too.

Fix it by defining mwifiex_cb structure and having
MWIFIEX_SKB_TXCB and MWIFIEX_SKB_RXCB return the correct address
of tx_info/rx_info using the structure members.

Also add a BUILD_BUG_ON to maks sure that mwifiex_cb structure
doesn't exceed the size of skb->cb.

Reviewed-by: Aaron Durbin <[e-mail]>
Signed-off-by: Chin-Ran Lo <[e-mail]>
Signed-off-by: Bing Zhao <[e-mail]>
Signed-off-by: John W. Linville <[e-mail]>

drivers/net/wireless/mwifiex/pcie.c

···
 		return -1;
 	}
 	mapping.len = size;
-	memcpy(skb->cb, &mapping, sizeof(mapping));
+	mwifiex_store_mapping(skb, &mapping);
 	return 0;
 }
 
···
 	struct pcie_service_card *card = adapter->card;
 	struct mwifiex_dma_mapping mapping;
 
-	MWIFIEX_SKB_PACB(skb, &mapping);
+	mwifiex_get_mapping(skb, &mapping);
 	pci_unmap_single(card->dev, mapping.addr, mapping.len, flags);
 }
 

drivers/net/wireless/mwifiex/util.h

···
 #ifndef _MWIFIEX_UTIL_H_
 #define _MWIFIEX_UTIL_H_
 
-static inline struct mwifiex_rxinfo *MWIFIEX_SKB_RXCB(struct sk_buff *skb)
-{
-	return (struct mwifiex_rxinfo *)(skb->cb + sizeof(dma_addr_t));
-}
-
-static inline struct mwifiex_txinfo *MWIFIEX_SKB_TXCB(struct sk_buff *skb)
-{
-	return (struct mwifiex_txinfo *)(skb->cb + sizeof(dma_addr_t));
-}
-
 struct mwifiex_dma_mapping {
 	dma_addr_t addr;
 	size_t len;
 };
 
-static inline void MWIFIEX_SKB_PACB(struct sk_buff *skb,
-					struct mwifiex_dma_mapping *mapping)
+struct mwifiex_cb {
+	struct mwifiex_dma_mapping dma_mapping;
+	union {
+		struct mwifiex_rxinfo rx_info;
+		struct mwifiex_txinfo tx_info;
+	};
+};
+
+static inline struct mwifiex_rxinfo *MWIFIEX_SKB_RXCB(struct sk_buff *skb)
 {
-	memcpy(mapping, skb->cb, sizeof(*mapping));
+	struct mwifiex_cb *cb = (struct mwifiex_cb *)skb->cb;
+
+	BUILD_BUG_ON(sizeof(struct mwifiex_cb) > sizeof(skb->cb));
+	return &cb->rx_info;
+}
+
+static inline struct mwifiex_txinfo *MWIFIEX_SKB_TXCB(struct sk_buff *skb)
+{
+	struct mwifiex_cb *cb = (struct mwifiex_cb *)skb->cb;
+
+	return &cb->tx_info;
+}
+
+static inline void mwifiex_store_mapping(struct sk_buff *skb,
+					 struct mwifiex_dma_mapping *mapping)
+{
+	struct mwifiex_cb *cb = (struct mwifiex_cb *)skb->cb;
+
+	memcpy(&cb->dma_mapping, mapping, sizeof(*mapping));
+}
+
+static inline void mwifiex_get_mapping(struct sk_buff *skb,
+				       struct mwifiex_dma_mapping *mapping)
+{
+	struct mwifiex_cb *cb = (struct mwifiex_cb *)skb->cb;
+
+	memcpy(mapping, &cb->dma_mapping, sizeof(*mapping));
 }
 
 static inline dma_addr_t MWIFIEX_SKB_DMA_ADDR(struct sk_buff *skb)
 {
 	struct mwifiex_dma_mapping mapping;
 
-	MWIFIEX_SKB_PACB(skb, &mapping);
+	mwifiex_get_mapping(skb, &mapping);
 
 	return mapping.addr;
 }