netfilter 07/09: simplify nf_conntrack_alloc() error handling

nf_conntrack_alloc cannot return NULL, so there is no need to check for
NULL before using the value.  I have also removed the initialization of ct
to NULL in nf_conntrack_alloc, since the value is never used, and since
perhaps it might lead one to think that return ct at the end might return
NULL.

The semantic patch that finds this problem is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@match exists@
expression x, E;
position p1,p2;
statement S1, S2;
@@

x@p1 = nf_conntrack_alloc(...)
... when != x = E
(
  if (x@p2 == NULL || ...) S1 else S2
|
  if (x@p2 == NULL && ...) S1 else S2
)

@other_match exists@
expression match.x, E1, E2;
position p1!=match.p1,match.p2;
@@

x@p1 = E1
... when != x = E2
x@p2

@ script:python depends on !other_match@
p1 << match.p1;
p2 << match.p2;
@@

print "%s: call to nf_conntrack_alloc %s bad test %s" % (p1[0].file,p1[0].line,p2[0].line)
// </smpl>
Signed-off-by: NJulia Lawall <julia@diku.dk>
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/netfilter/nf_conntrack_core.c

@@ -469,7 +469,7 @@ struct nf_conn *nf_conntrack_alloc(struct net *net,
 				   const struct nf_conntrack_tuple *repl,
 				   gfp_t gfp)
 {
-	struct nf_conn *ct = NULL;
+	struct nf_conn *ct;
 
 	if (unlikely(!nf_conntrack_hash_rnd_initted)) {
 		get_random_bytes(&nf_conntrack_hash_rnd, 4);
@@ -551,7 +551,7 @@ init_conntrack(struct net *net,
 	}
 
 	ct = nf_conntrack_alloc(net, tuple, &repl_tuple, GFP_ATOMIC);
-	if (ct == NULL || IS_ERR(ct)) {
+	if (IS_ERR(ct)) {
 		pr_debug("Can't allocate conntrack.\n");
 		return (struct nf_conntrack_tuple_hash *)ct;
 	}

net/netfilter/nf_conntrack_netlink.c

@@ -1134,7 +1134,7 @@ ctnetlink_create_conntrack(struct nlattr *cda[],
 	struct nf_conntrack_helper *helper;
 
 	ct = nf_conntrack_alloc(&init_net, otuple, rtuple, GFP_ATOMIC);
-	if (ct == NULL || IS_ERR(ct))
+	if (IS_ERR(ct))
 		return -ENOMEM;
 
 	if (!cda[CTA_TIMEOUT])