netfilter: nfnetlink_cthelper: hit EBUSY on updates if size mismatches

The private helper data size cannot be updated. However, updates that
contain NFCTH_PRIV_DATA_LEN might bogusly hit EBUSY even if the size is
the same.

Fixes: 12f7a505331e ("netfilter: add user-space connection tracking helper infrastructure")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nfnetlink_cthelper.c b/net/netfilter/nfnetlink_cthelper.c
index 322ac5d..752b10c 100644 (file)
--- a/net/netfilter/nfnetlink_cthelper.c
+++ b/net/netfilter/nfnetlink_cthelper.c
@@ -380,10 +380,14 @@ static int
 nfnl_cthelper_update(const struct nlattr * const tb[],
                     struct nf_conntrack_helper *helper)
 {
+       u32 size;
        int ret;
 
-       if (tb[NFCTH_PRIV_DATA_LEN])
-               return -EBUSY;
+       if (tb[NFCTH_PRIV_DATA_LEN]) {
+               size = ntohl(nla_get_be32(tb[NFCTH_PRIV_DATA_LEN]));
+               if (size != helper->data_len)
+                       return -EBUSY;
+       }
 
        if (tb[NFCTH_POLICY]) {
                ret = nfnl_cthelper_update_policy(helper, tb[NFCTH_POLICY]);