uevent: add alloc_uevent_skb() helper

This patch adds alloc_uevent_skb() in preparation for follow up patches.
Signed-off-by: NChristian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

lib/kobject_uevent.c

@@ -22,6 +22,7 @@
 #include <linux/socket.h>
 #include <linux/skbuff.h>
 #include <linux/netlink.h>
+#include <linux/uidgid.h>
 #include <linux/uuid.h>
 #include <linux/ctype.h>
 #include <net/sock.h>
@@ -296,6 +297,38 @@ static void cleanup_uevent_env(struct subprocess_info *info)
 }
 #endif
 
+#ifdef CONFIG_NET
+static struct sk_buff *alloc_uevent_skb(struct kobj_uevent_env *env,
+					const char *action_string,
+					const char *devpath)
+{
+	struct netlink_skb_parms *parms;
+	struct sk_buff *skb = NULL;
+	char *scratch;
+	size_t len;
+
+	/* allocate message with maximum possible size */
+	len = strlen(action_string) + strlen(devpath) + 2;
+	skb = alloc_skb(len + env->buflen, GFP_KERNEL);
+	if (!skb)
+		return NULL;
+
+	/* add header */
+	scratch = skb_put(skb, len);
+	sprintf(scratch, "%s@%s", action_string, devpath);
+
+	skb_put_data(skb, env->buf, env->buflen);
+
+	parms = &NETLINK_CB(skb);
+	parms->creds.uid = GLOBAL_ROOT_UID;
+	parms->creds.gid = GLOBAL_ROOT_GID;
+	parms->dst_group = 1;
+	parms->portid = 0;
+
+	return skb;
+}
+#endif
+
 static int kobject_uevent_net_broadcast(struct kobject *kobj,
 					struct kobj_uevent_env *env,
 					const char *action_string,
@@ -314,22 +347,10 @@ static int kobject_uevent_net_broadcast(struct kobject *kobj,
 			continue;
 
 		if (!skb) {
-			/* allocate message with the maximum possible size */
-			size_t len = strlen(action_string) + strlen(devpath) + 2;
-			char *scratch;
-
 			retval = -ENOMEM;
-			skb = alloc_skb(len + env->buflen, GFP_KERNEL);
+			skb = alloc_uevent_skb(env, action_string, devpath);
 			if (!skb)
 				continue;
-
-			/* add header */
-			scratch = skb_put(skb, len);
-			sprintf(scratch, "%s@%s", action_string, devpath);
-
-			skb_put_data(skb, env->buf, env->buflen);
-
-			NETLINK_CB(skb).dst_group = 1;
 		}
 
 		retval = netlink_broadcast_filtered(uevent_sock, skb_get(skb),