Merge branch 'inet-frags-followup'

Eric Dumazet says:

====================
inet: frags: followup to 'inet-frags-avoid-possible-races-at-netns-dismantle'

Latest patch series ('inet-frags-avoid-possible-races-at-netns-dismantle')
brought another syzbot report shown in the third patch changelog.

While fixing the issue, I had to call inet_frags_fini() later
in IPv6 and ilowpan.

Also I believe a completion is needed to ensure proper dismantle
at module removal.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 39 insertions, 4 deletions

diff --git a/net/ieee802154/6lowpan/reassembly.c b/net/ieee802154/6lowpan/reassembly.c
index e59c3b708969..5b56f16ed86b 100644
--- a/net/ieee802154/6lowpan/reassembly.c
+++ b/net/ieee802154/6lowpan/reassembly.c
@@ -540,7 +540,7 @@ err_sysctl:
 
 void lowpan_net_frag_exit(void)
 {
-	inet_frags_fini(&lowpan_frags);
 	lowpan_frags_sysctl_unregister();
 	unregister_pernet_subsys(&lowpan_frags_ops);
+	inet_frags_fini(&lowpan_frags);
 }
diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 6ca9523374da..2b816f1ebbb4 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -110,14 +110,18 @@ int inet_frags_init(struct inet_frags *f)
 	if (!f->frags_cachep)
 		return -ENOMEM;
 
+	refcount_set(&f->refcnt, 1);
+	init_completion(&f->completion);
 	return 0;
 }
 EXPORT_SYMBOL(inet_frags_init);
 
 void inet_frags_fini(struct inet_frags *f)
 {
-	/* We must wait that all inet_frag_destroy_rcu() have completed. */
-	rcu_barrier();
+	if (refcount_dec_and_test(&f->refcnt))
+		complete(&f->completion);
+
+	wait_for_completion(&f->completion);
 
 	kmem_cache_destroy(f->frags_cachep);
 	f->frags_cachep = NULL;
@@ -149,11 +153,42 @@ static void fqdir_rwork_fn(struct work_struct *work)
 {
 	struct fqdir *fqdir = container_of(to_rcu_work(work),
 					   struct fqdir, destroy_rwork);
+	struct inet_frags *f = fqdir->f;
 
 	rhashtable_free_and_destroy(&fqdir->rhashtable, inet_frags_free_cb, NULL);
+
+	/* We need to make sure all ongoing call_rcu(..., inet_frag_destroy_rcu)
+	 * have completed, since they need to dereference fqdir.
+	 * Would it not be nice to have kfree_rcu_barrier() ? :)
+	 */
+	rcu_barrier();
+
+	if (refcount_dec_and_test(&f->refcnt))
+		complete(&f->completion);
+
 	kfree(fqdir);
 }
 
+int fqdir_init(struct fqdir **fqdirp, struct inet_frags *f, struct net *net)
+{
+	struct fqdir *fqdir = kzalloc(sizeof(*fqdir), GFP_KERNEL);
+	int res;
+
+	if (!fqdir)
+		return -ENOMEM;
+	fqdir->f = f;
+	fqdir->net = net;
+	res = rhashtable_init(&fqdir->rhashtable, &fqdir->f->rhash_params);
+	if (res < 0) {
+		kfree(fqdir);
+		return res;
+	}
+	refcount_inc(&f->refcnt);
+	*fqdirp = fqdir;
+	return 0;
+}
+EXPORT_SYMBOL(fqdir_init);
+
 void fqdir_exit(struct fqdir *fqdir)
 {
 	fqdir->high_thresh = 0; /* prevent creation of new frags */
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 836ea964cf14..ff5b6d8de2c6 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -583,8 +583,8 @@ err_protocol:
 
 void ipv6_frag_exit(void)
 {
-	inet_frags_fini(&ip6_frags);
 	ip6_frags_sysctl_unregister();
 	unregister_pernet_subsys(&ip6_frags_ops);
 	inet6_del_protocol(&frag_protocol, IPPROTO_FRAGMENT);
+	inet_frags_fini(&ip6_frags);
 }