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authorJohannes Berg <johannes.berg@intel.com>2015-01-16 10:37:13 (GMT)
committerDavid S. Miller <davem@davemloft.net>2015-01-16 22:04:24 (GMT)
commit5ad6300524c0332ac67e912c20d6e5cf262ba58f (patch)
tree6070fdb74e9f4051dca1bf69fea06b39212f3c65 /net/netlink
parentf555f3d76aaade29c7e221a37ee64fe722955c09 (diff)
genetlink: disallow subscribing to unknown mcast groups
Jeff Layton reported that he could trigger the multicast unbind warning in generic netlink using trinity. I originally thought it was a race condition between unregistering the generic netlink family and closing the socket, but there's a far simpler explanation: genetlink currently allows subscribing to groups that don't (yet) exist, and the warning is triggered when unsubscribing again while the group still doesn't exist. Originally, I had a warning in the subscribe case and accepted it out of userspace API concerns, but the warning was of course wrong and removed later. However, I now think that allowing userspace to subscribe to groups that don't exist is wrong and could possibly become a security problem: Consider a (new) genetlink family implementing a permission check in the mcast_bind() function similar to the like the audit code does today; it would be possible to bypass the permission check by guessing the ID and subscribing to the group it exists. This is only possible in case a family like that would be dynamically loaded, but it doesn't seem like a huge stretch, for example wireless may be loaded when you plug in a USB device. To avoid this reject such subscription attempts. If this ends up causing userspace issues we may need to add a workaround in af_netlink to deny such requests but not return an error. Reported-by: Jeff Layton <jeff.layton@primarydata.com> Signed-off-by: Johannes Berg <johannes.berg@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/netlink')
-rw-r--r--net/netlink/genetlink.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 2e11061e..c18d3f5 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -985,7 +985,7 @@ static struct genl_multicast_group genl_ctrl_groups[] = {
static int genl_bind(struct net *net, int group)
{
- int i, err = 0;
+ int i, err = -ENOENT;
down_read(&cb_lock);
for (i = 0; i < GENL_FAM_TAB_SIZE; i++) {

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