NETFILTER: xt_connbytes: fix division by zero

When the packet counter of a connection is zero a division by zero
occurs in div64_64(). Fix that by using zero as average value, which
is correct as long as the packet counter didn't overflow, at which
point we have lost anyway.

Based on patch from Jonas Berlin <xkr47@outerspace.dyndns.org>,
with suggestions from KOVACS Krisztian <hidden@balabit.hu>.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

diff --git a/net/netfilter/xt_connbytes.c b/net/netfilter/xt_connbytes.c
index 150d2a4b0f71059edaad4a8995a794f7fe456030..9ea158eb5ebe4ddd7115f232a9ff1255a4cfc824 100644 (file)
--- a/net/netfilter/xt_connbytes.c
+++ b/net/netfilter/xt_connbytes.c
@@ -51,6 +51,8 @@ match(const struct sk_buff *skb,
 {
        const struct xt_connbytes_info *sinfo = matchinfo;
        u_int64_t what = 0;     /* initialize to make gcc happy */
+       u_int64_t bytes = 0;
+       u_int64_t pkts = 0;
        const struct ip_conntrack_counter *counters;
 
        if (!(counters = nf_ct_get_counters(skb)))
@@ -88,29 +90,22 @@ match(const struct sk_buff *skb,
        case XT_CONNBYTES_AVGPKT:
                switch (sinfo->direction) {
                case XT_CONNBYTES_DIR_ORIGINAL:
-                       what = div64_64(counters[IP_CT_DIR_ORIGINAL].bytes,
-                                       counters[IP_CT_DIR_ORIGINAL].packets);
+                       bytes = counters[IP_CT_DIR_ORIGINAL].bytes;
+                       pkts  = counters[IP_CT_DIR_ORIGINAL].packets;
                        break;
                case XT_CONNBYTES_DIR_REPLY:
-                       what = div64_64(counters[IP_CT_DIR_REPLY].bytes,
-                                       counters[IP_CT_DIR_REPLY].packets);
+                       bytes = counters[IP_CT_DIR_REPLY].bytes;
+                       pkts  = counters[IP_CT_DIR_REPLY].packets;
                        break;
                case XT_CONNBYTES_DIR_BOTH:
-                       {
-                               u_int64_t bytes;
-                               u_int64_t pkts;
-                               bytes = counters[IP_CT_DIR_ORIGINAL].bytes +
-                                       counters[IP_CT_DIR_REPLY].bytes;
-                               pkts = counters[IP_CT_DIR_ORIGINAL].packets+
-                                       counters[IP_CT_DIR_REPLY].packets;
-
-                               /* FIXME_THEORETICAL: what to do if sum
-                                * overflows ? */
-
-                               what = div64_64(bytes, pkts);
-                       }
+                       bytes = counters[IP_CT_DIR_ORIGINAL].bytes +
+                               counters[IP_CT_DIR_REPLY].bytes;
+                       pkts  = counters[IP_CT_DIR_ORIGINAL].packets +
+                               counters[IP_CT_DIR_REPLY].packets;
                        break;
                }
+               if (pkts != 0)
+                       what = div64_64(bytes, pkts);
                break;
        }