net: fix decnet rtnexthop parsing

dn_fib_count_nhs() could enter an infinite loop if nhp->rtnh_len == 0
(i.e. if userspace passes a malformed netlink message).

Let's use the helpers from net/nexthop.h which take care of all this
stuff. We can do exactly the same as e.g. fib_count_nexthops() and
fib_get_nhs() from net/ipv4/fib_semantics.c.

This fixes the softlockup for me.

Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/decnet/dn_fib.c b/net/decnet/dn_fib.c
index df48034378889eac83c6b262a76a32028202efb4..a796fc7cbc3542972eaa19bbc3d3dc07a428ff1c 100644 (file)
--- a/net/decnet/dn_fib.c
+++ b/net/decnet/dn_fib.c
@@ -41,6 +41,7 @@
 #include <net/dn_fib.h>
 #include <net/dn_neigh.h>
 #include <net/dn_dev.h>
+#include <net/nexthop.h>
 
 #define RT_MIN_TABLE 1
 
@@ -150,14 +151,13 @@ static int dn_fib_count_nhs(const struct nlattr *attr)
        struct rtnexthop *nhp = nla_data(attr);
        int nhs = 0, nhlen = nla_len(attr);
 
-       while(nhlen >= (int)sizeof(struct rtnexthop)) {
-               if ((nhlen -= nhp->rtnh_len) < 0)
-                       return 0;
+       while (rtnh_ok(nhp, nhlen)) {
                nhs++;
-               nhp = RTNH_NEXT(nhp);
+               nhp = rtnh_next(nhp, &nhlen);
        }
 
-       return nhs;
+       /* leftover implies invalid nexthop configuration, discard it */
+       return nhlen > 0 ? 0 : nhs;
 }
 
 static int dn_fib_get_nhs(struct dn_fib_info *fi, const struct nlattr *attr,
@@ -167,21 +167,24 @@ static int dn_fib_get_nhs(struct dn_fib_info *fi, const struct nlattr *attr,
        int nhlen = nla_len(attr);
 
        change_nexthops(fi) {
-               int attrlen = nhlen - sizeof(struct rtnexthop);
-               if (attrlen < 0 || (nhlen -= nhp->rtnh_len) < 0)
+               int attrlen;
+
+               if (!rtnh_ok(nhp, nhlen))
                        return -EINVAL;
 
                nh->nh_flags  = (r->rtm_flags&~0xFF) | nhp->rtnh_flags;
                nh->nh_oif    = nhp->rtnh_ifindex;
                nh->nh_weight = nhp->rtnh_hops + 1;
 
-               if (attrlen) {
+               attrlen = rtnh_attrlen(nhp);
+               if (attrlen > 0) {
                        struct nlattr *gw_attr;
 
                        gw_attr = nla_find((struct nlattr *) (nhp + 1), attrlen, RTA_GATEWAY);
                        nh->nh_gw = gw_attr ? nla_get_le16(gw_attr) : 0;
                }
-               nhp = RTNH_NEXT(nhp);
+
+               nhp = rtnh_next(nhp, &nhlen);
        } endfor_nexthops(fi);
 
        return 0;