[ 10/37] net: fix rtnetlink IFF_PROMISC and IFF_ALLMULTI handling

[Ben Hutchings <ben@decadent.org.uk>]

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiri Benc <jbenc@redhat.com>

[ Upstream commit b1beb681cba5358f62e6187340660ade226a5fcc ]

When device flags are set using rtnetlink, IFF_PROMISC and IFF_ALLMULTI
flags are handled specially. Function dev_change_flags sets IFF_PROMISC and
IFF_ALLMULTI bits in dev->gflags according to the passed value but
do_setlink passes a result of rtnl_dev_combine_flags which takes those bits
from dev->flags.

This can be easily trigerred by doing:

tcpdump -i eth0 &
ip l s up eth0

ip sets IFF_UP flag in ifi_flags and ifi_change, which is combined with
IFF_PROMISC by rtnl_dev_combine_flags, causing __dev_change_flags to set
IFF_PROMISC in gflags.

Reported-by: Max Matveev <makc@redhat.com>
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/core/rtnetlink.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 2ef859a..88bcf76 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -670,6 +670,12 @@ static void set_operstate(struct net_device *dev, unsigned char transition)
 	}
 }
 
+static unsigned int rtnl_dev_get_flags(const struct net_device *dev)
+{
+	return (dev->flags & ~(IFF_PROMISC | IFF_ALLMULTI)) |
+	       (dev->gflags & (IFF_PROMISC | IFF_ALLMULTI));
+}
+
 static unsigned int rtnl_dev_combine_flags(const struct net_device *dev,
 					   const struct ifinfomsg *ifm)
 {
@@ -678,7 +684,7 @@ static unsigned int rtnl_dev_combine_flags(const struct net_device *dev,
 	/* bugwards compatibility: ifi_change == 0 is treated as ~0 */
 	if (ifm->ifi_change)
 		flags = (flags & ifm->ifi_change) |
-			(dev->flags & ~ifm->ifi_change);
+			(rtnl_dev_get_flags(dev) & ~ifm->ifi_change);
 
 	return flags;
 }