ipv4/route: Allow NULL flowinfo in rt_fill_info()

In the next patch, we're going to use rt_fill_info() to dump exception
routes upon RTM_GETROUTE with NLM_F_ROOT, meaning userspace is requesting
a dump and not a specific route selection, which in turn implies the input
interface is not relevant. Update rt_fill_info() to handle a NULL
flowinfo.

v7: If fl4 is NULL, explicitly set r->rtm_tos to 0: it's not initialised
    otherwise (spotted by David Ahern)

v6: New patch

Suggested-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -2699,7 +2699,7 @@ static int rt_fill_info(struct net *net, __be32 dst, __be32 src,
  r->rtm_family = AF_INET;
  r->rtm_dst_len = 32;
  r->rtm_src_len = 0;
- r->rtm_tos = fl4->flowi4_tos;
+ r->rtm_tos = fl4 ? fl4->flowi4_tos : 0;
  r->rtm_table = table_id < 256 ? table_id : RT_TABLE_COMPAT;
  if (nla_put_u32(skb, RTA_TABLE, table_id))
  goto nla_put_failure;
@@ -2727,7 +2727,7 @@ static int rt_fill_info(struct net *net, __be32 dst, __be32 src,
  nla_put_u32(skb, RTA_FLOW, rt->dst.tclassid))
  goto nla_put_failure;
 #endif
- if (!rt_is_input_route(rt) &&
+ if (fl4 && !rt_is_input_route(rt) &&
  fl4->saddr != src) {
  if (nla_put_in_addr(skb, RTA_PREFSRC, fl4->saddr))
  goto nla_put_failure;
@@ -2767,36 +2767,40 @@ static int rt_fill_info(struct net *net, __be32 dst, __be32 src,
  if (rtnetlink_put_metrics(skb, metrics) < 0)
  goto nla_put_failure;
 
- if (fl4->flowi4_mark &&
- nla_put_u32(skb, RTA_MARK, fl4->flowi4_mark))
- goto nla_put_failure;
-
- if (!uid_eq(fl4->flowi4_uid, INVALID_UID) &&
- nla_put_u32(skb, RTA_UID,
- from_kuid_munged(current_user_ns(), fl4->flowi4_uid)))
- goto nla_put_failure;
+ if (fl4) {
+ if (fl4->flowi4_mark &&
+ nla_put_u32(skb, RTA_MARK, fl4->flowi4_mark))
+ goto nla_put_failure;
 
- error = rt->dst.error;
+ if (!uid_eq(fl4->flowi4_uid, INVALID_UID) &&
+ nla_put_u32(skb, RTA_UID,
+ from_kuid_munged(current_user_ns(),
+ fl4->flowi4_uid)))
+ goto nla_put_failure;
 
- if (rt_is_input_route(rt)) {
+  if (rt_is_input_route(rt)) {
 #ifdef CONFIG_IP_MROUTE
- if (ipv4_is_multicast(dst) && !ipv4_is_local_multicast(dst) &&
- IPV4_DEVCONF_ALL(net, MC_FORWARDING)) {
- int err = ipmr_get_route(net, skb,
- fl4->saddr, fl4->daddr,
- r, portid);
-
- if (err <= 0) {
- if (err == 0)
- return 0;
- goto nla_put_failure;
- }
- } else
+ if (ipv4_is_multicast(dst) &&
+ !ipv4_is_local_multicast(dst) &&
+ IPV4_DEVCONF_ALL(net, MC_FORWARDING)) {
+ int err = ipmr_get_route(net, skb,
+ fl4->saddr, fl4->daddr,
+ r, portid);
+
+ if (err <= 0) {
+ if (err == 0)
+ return 0;
+ goto nla_put_failure;
+ }
+ } else
 #endif
- if (nla_put_u32(skb, RTA_IIF, fl4->flowi4_iif))
- goto nla_put_failure;
+ if (nla_put_u32(skb, RTA_IIF, fl4->flowi4_iif))
+ goto nla_put_failure;
+ }
  }
 
+ error = rt->dst.error;
+
  if (rtnl_put_cacheinfo(skb, &rt->dst, 0, expires, error) < 0)
  goto nla_put_failure;