genetlink: fix usage of NLM_F_EXCL or NLM_F_REPLACE

Currently, it is not possible to use neither NLM_F_EXCL nor
NLM_F_REPLACE from genetlink. This is due to this checking in
genl_family_rcv_msg:

	if (nlh->nlmsg_flags & NLM_F_DUMP)

NLM_F_DUMP is NLM_F_MATCH|NLM_F_ROOT. Thus, if NLM_F_EXCL or
NLM_F_REPLACE flag is set, genetlink believes that you're
requesting a dump and it calls the .dumpit callback.

The solution that I propose is to refine this checking to
make it stricter:

	if ((nlh->nlmsg_flags & NLM_F_DUMP) == NLM_F_DUMP)

And given the combination NLM_F_REPLACE and NLM_F_EXCL does
not make sense to me, it removes the ambiguity.

There was a patch that tried to fix this some time ago (0ab03c2
netlink: test for all flags of the NLM_F_DUMP composite) but it
tried to resolve this ambiguity in *all* existing netlink subsystems,
not only genetlink. That patch was reverted since it broke iproute2,
which is using NLM_F_ROOT to request the dump of the routing cache.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 1076fe16b1228b09581b9a355b13855e761ee1ce..512718adb0d59df5120e047c69c973556d1c6fb6 100644 (file)
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -571,7 +571,7 @@ static int genl_family_rcv_msg(struct genl_family *family,
            !capable(CAP_NET_ADMIN))
                return -EPERM;
 
-       if (nlh->nlmsg_flags & NLM_F_DUMP) {
+       if ((nlh->nlmsg_flags & NLM_F_DUMP) == NLM_F_DUMP) {
                struct netlink_dump_control c = {
                        .dump = ops->dumpit,
                        .done = ops->done,