netfilter: xt_recent: don't reject rule if new hitcount exceeds table max

given:
-A INPUT -m recent --update --seconds 30 --hitcount 4
and
iptables-save > foo

then
iptables-restore < foo

will fail with:
kernel: xt_recent: hitcount (4) is larger than packets to be remembered (4) for table DEFAULT

Even when the check is fixed, the restore won't work if the hitcount is
increased to e.g. 6, since by the time checkentry runs it will find the
'old' incarnation of the table.

We can avoid this by increasing the maximum threshold silently; we only
have to rm all the current entries of the table (these entries would
not have enough room to handle the increased hitcount).

This even makes (not-very-useful)
-A INPUT -m recent --update --seconds 30 --hitcount 4
-A INPUT -m recent --update --seconds 30 --hitcount 42
work.

Fixes: abc86d0f99242b7f142b (netfilter: xt_recent: relax ip_pkt_list_tot restrictions)
Tracked-down-by: Chris Vine <chris@cvine.freeserve.co.uk>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/xt_recent.c b/net/netfilter/xt_recent.c
index 30dbe34915ae2b1fcf4d0ca3149369bdf3913f0f..45e1b30e4fb214f850af2590425ab2a9748c6476 100644 (file)
--- a/net/netfilter/xt_recent.c
+++ b/net/netfilter/xt_recent.c
@@ -378,12 +378,11 @@ static int recent_mt_check(const struct xt_mtchk_param *par,
        mutex_lock(&recent_mutex);
        t = recent_table_lookup(recent_net, info->name);
        if (t != NULL) {
-               if (info->hit_count > t->nstamps_max_mask) {
-                       pr_info("hitcount (%u) is larger than packets to be remembered (%u) for table %s\n",
-                               info->hit_count, t->nstamps_max_mask + 1,
-                               info->name);
-                       ret = -EINVAL;
-                       goto out;
+               if (nstamp_mask > t->nstamps_max_mask) {
+                       spin_lock_bh(&recent_lock);
+                       recent_table_flush(t);
+                       t->nstamps_max_mask = nstamp_mask;
+                       spin_unlock_bh(&recent_lock);
                }
 
                t->refcnt++;