[PATCH] wireless: WE-20 compatibility for ESSID and NICKN ioctls

WE-21 changed the ABI for the SIOC[SG]IW{ESSID,NICKN} ioctls by dropping
NULL termination.  This patch adds compatibility code so that WE-21 can
work properly with WE-20 (and older) tools.
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/core/wireless.c

@@ -748,11 +748,39 @@ static int ioctl_standard_call(struct net_device *	dev,
 		int	extra_size;
 		int	user_length = 0;
 		int	err;
+		int	essid_compat = 0;
 
 		/* Calculate space needed by arguments. Always allocate
 		 * for max space. Easier, and won't last long... */
 		extra_size = descr->max_tokens * descr->token_size;
 
+		/* Check need for ESSID compatibility for WE < 21 */
+		switch (cmd) {
+		case SIOCSIWESSID:
+		case SIOCGIWESSID:
+		case SIOCSIWNICKN:
+		case SIOCGIWNICKN:
+			if (iwr->u.data.length == descr->max_tokens + 1)
+				essid_compat = 1;
+			else if (IW_IS_SET(cmd) && (iwr->u.data.length != 0)) {
+				char essid[IW_ESSID_MAX_SIZE + 1];
+
+				err = copy_from_user(essid, iwr->u.data.pointer,
+						     iwr->u.data.length *
+						     descr->token_size);
+				if (err)
+					return -EFAULT;
+
+				if (essid[iwr->u.data.length - 1] == '\0')
+					essid_compat = 1;
+			}
+			break;
+		default:
+			break;
+		}
+
+		iwr->u.data.length -= essid_compat;
+
 		/* Check what user space is giving us */
 		if(IW_IS_SET(cmd)) {
 			/* Check NULL pointer */
@@ -795,7 +823,8 @@ static int ioctl_standard_call(struct net_device *	dev,
 #endif	/* WE_IOCTL_DEBUG */
 
 		/* Create the kernel buffer */
-		extra = kmalloc(extra_size, GFP_KERNEL);
+		/*    kzalloc ensures NULL-termination for essid_compat */
+		extra = kzalloc(extra_size, GFP_KERNEL);
 		if (extra == NULL) {
 			return -ENOMEM;
 		}
@@ -819,6 +848,8 @@ static int ioctl_standard_call(struct net_device *	dev,
 		/* Call the handler */
 		ret = handler(dev, &info, &(iwr->u), extra);
 
+		iwr->u.data.length += essid_compat;
+
 		/* If we have something to return to the user */
 		if (!ret && IW_IS_GET(cmd)) {
 			/* Check if there is enough buffer up there */