: Allow changing of subsets of netdevice flags in rtnl_setlink

[RTNETLINK]: Allow changing of subsets of netdevice flags in rtnl_setlink

rtnl_setlink doesn't allow to change subsets of the flags, just to override the set entirely by a new one. This means that for simply setting a device up or down userspace first needs to query the current flags, change it and send the changed flags back, which is racy and needlessly complicated.

Mask the flags using ifi_change since this is what it is intended for. For backwards compatibility treat ifi_change == 0 as ~0 (even though it seems quite unlikely that anyone has been using this so far).

---
commit c80dabd4a038beb68da24327216f594119a8e05a
tree 2def6c042eb3276ef733af38fe2f27f746b89612
parent 192ecca1d62ada577a664410ed90b9a83315a65a
author Patrick McHardy <[email protected]> Thu, 17 May 2007 05:31:30 +0200 committer Patrick McHardy <[email protected]> Thu, 17 May 2007 22:06:27 +0200

 net/core/rtnetlink.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

index e2996bb..10fe3d3 100644
@@ -685,8 +685,15 @@ static int rtnl_setlink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 	}
 
 
-	if (ifm->ifi_flags)
-		dev_change_flags(dev, ifm->ifi_flags);
+	if (ifm->ifi_flags || ifm->ifi_change) {
+		unsigned int flags = ifm->ifi_flags;
+
+		/* bugwards compatibility: ifi_change == 0 is treated as ~0 */
+		if (ifm->ifi_change)
+			flags = (flags & ifm->ifi_change) |
+				(dev->flags & ~ifm->ifi_change);
+		dev_change_flags(dev, flags);
+	}
 
 	if (tb[IFLA_TXQLEN])
 		dev->tx_queue_len = nla_get_u32(tb[IFLA_TXQLEN]);

Applied, thanks for finding this interface deficiency. :-)