[PATCH v3] staging: rtl8192e: Fix return type for implementation of ndo_start_xmit

[GUO Zihua <guozihua@huawei.com>]

CFI (Control Flow Integrity) is a safety feature allowing the system to
detect and react should a potential control flow hijacking occurs. In
particular, the Forward-Edge CFI protects indirect function calls by
ensuring the prototype of function that is actually called matches the
definition of the function hook.

Since Linux now supports CFI, it will be a good idea to fix mismatched
return type for implementation of hooks. Otherwise this would get
cought out by CFI and cause a panic.

Use enums from netdev_tx_t as return value instead, then change return
type to netdev_tx_t. Note that rtllib_xmit_inter() would return 1 only
on allocation failure and the queue is stopped if that happens, meeting
the documented requirement if NETDEV_TX_BUSY should be returned by
ndo_start_xmit.

Signed-off-by: GUO Zihua <guozihua@huawei.com>
---

v3:
  Provide detail on CFI.

v2:
  Fix truncated subject.

---
 drivers/staging/rtl8192e/rtllib.h    | 2 +-
 drivers/staging/rtl8192e/rtllib_tx.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/rtl8192e/rtllib.h b/drivers/staging/rtl8192e/rtllib.h
index 0ecd81a81866..b4b606f552fb 100644
--- a/drivers/staging/rtl8192e/rtllib.h
+++ b/drivers/staging/rtl8192e/rtllib.h
@@ -1938,7 +1938,7 @@ int rtllib_encrypt_fragment(
 	struct sk_buff *frag,
 	int hdr_len);
 
-int rtllib_xmit(struct sk_buff *skb,  struct net_device *dev);
+netdev_tx_t rtllib_xmit(struct sk_buff *skb,  struct net_device *dev);
 void rtllib_txb_free(struct rtllib_txb *txb);
 
 /* rtllib_rx.c */
diff --git a/drivers/staging/rtl8192e/rtllib_tx.c b/drivers/staging/rtl8192e/rtllib_tx.c
index 42f81b23a144..9da83531932f 100644
--- a/drivers/staging/rtl8192e/rtllib_tx.c
+++ b/drivers/staging/rtl8192e/rtllib_tx.c
@@ -962,9 +962,9 @@ static int rtllib_xmit_inter(struct sk_buff *skb, struct net_device *dev)
 
 }
 
-int rtllib_xmit(struct sk_buff *skb, struct net_device *dev)
+netdev_tx_t rtllib_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	memset(skb->cb, 0, sizeof(skb->cb));
-	return rtllib_xmit_inter(skb, dev);
+	return rtllib_xmit_inter(skb, dev) ? NETDEV_TX_BUSY : NETDEV_TX_OK;
 }
 EXPORT_SYMBOL(rtllib_xmit);
-- 
2.17.1