diff options
author | Johannes Berg <johannes.berg@intel.com> | 2015-01-16 10:37:13 (GMT) |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2015-01-16 22:04:24 (GMT) |
commit | 5ad6300524c0332ac67e912c20d6e5cf262ba58f (patch) | |
tree | 6070fdb74e9f4051dca1bf69fea06b39212f3c65 | |
parent | f555f3d76aaade29c7e221a37ee64fe722955c09 (diff) | |
download | linux-5ad6300524c0332ac67e912c20d6e5cf262ba58f.tar.xz |
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>
-rw-r--r-- | net/netlink/genetlink.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c index 2e11061..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++) { |