Subject: [PATCH v1 1/2] net: sched: do not use tcf_proto 'tp' argument from call_rcu

From: John Fastabend <[email-masked]>
Date: Thu, 02 Oct 2014 22:45:59 -0700

Using the tcf_proto pointer 'tp' from inside the classifiers callback
is not valid because it may have been cleaned up by another call_rcu
occuring on another CPU.

'tp' is currently being used by tcf_unbind_filter() in this patch we
move instances of tcf_unbind_filter outside of the call_rcu() context.
This is safe to do because any running schedulers will either read the
valid class field or it will be zeroed.

And all schedulers today when the class is 0 do a lookup using the
same call used by the tcf_exts_bind(). So even if we have a running
classifier hit the null class pointer it will do a lookup and get
to the same result. This is particularly fragile at the moment because
the only way to verify this is to audit the schedulers call sites.

Reported-by: Cong Wang <[email-masked]>
Signed-off-by: John Fastabend <[email-masked]>
---
 net/sched/cls_basic.c |    4 +++-
 net/sched/cls_bpf.c   |    4 +++-
 net/sched/cls_fw.c    |    5 +++--
 net/sched/cls_route.c |    8 +++++---
 4 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/net/sched/cls_basic.c b/net/sched/cls_basic.c
index fe20826..81ddfa6 100644
--- a/net/sched/cls_basic.c
+++ b/net/sched/cls_basic.c
@@ -93,7 +93,6 @@ static void basic_delete_filter(struct rcu_head *head)
 	struct basic_filter *f = container_of(head, struct basic_filter, rcu);
 	struct tcf_proto *tp = f->tp;
 
-	tcf_unbind_filter(tp, &f->res);
 	tcf_exts_destroy(&f->exts);
 	tcf_em_tree_destroy(tp, &f->ematches);
 	kfree(f);
@@ -106,6 +105,7 @@ static void basic_destroy(struct tcf_proto *tp)
 
 	list_for_each_entry_safe(f, n, &head->flist, link) {
 		list_del_rcu(&f->link);
+		tcf_unbind_filter(tp, &f->res);
 		call_rcu(&f->rcu, basic_delete_filter);
 	}
 	RCU_INIT_POINTER(tp->root, NULL);
@@ -120,6 +120,7 @@ static int basic_delete(struct tcf_proto *tp, unsigned long arg)
 	list_for_each_entry(t, &head->flist, link)
 		if (t == f) {
 			list_del_rcu(&t->link);
+			tcf_unbind_filter(tp, &t->res);
 			call_rcu(&t->rcu, basic_delete_filter);
 			return 0;
 		}
@@ -222,6 +223,7 @@ static int basic_change(struct net *net, struct sk_buff *in_skb,
 
 	if (fold) {
 		list_replace_rcu(&fold->link, &fnew->link);
+		tcf_unbind_filter(tp, &fold->res);
 		call_rcu(&fold->rcu, basic_delete_filter);
 	} else {
 		list_add_rcu(&fnew->link, &head->flist);
diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index 4318d06..eed49d1 100644
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -92,7 +92,6 @@ static int cls_bpf_init(struct tcf_proto *tp)
 
 static void cls_bpf_delete_prog(struct tcf_proto *tp, struct cls_bpf_prog *prog)
 {
-	tcf_unbind_filter(tp, &prog->res);
 	tcf_exts_destroy(&prog->exts);
 
 	bpf_prog_destroy(prog->filter);
@@ -116,6 +115,7 @@ static int cls_bpf_delete(struct tcf_proto *tp, unsigned long arg)
 	list_for_each_entry(prog, &head->plist, link) {
 		if (prog == todel) {
 			list_del_rcu(&prog->link);
+			tcf_unbind_filter(tp, &prog->res);
 			call_rcu(&prog->rcu, __cls_bpf_delete_prog);
 			return 0;
 		}
@@ -131,6 +131,7 @@ static void cls_bpf_destroy(struct tcf_proto *tp)
 
 	list_for_each_entry_safe(prog, tmp, &head->plist, link) {
 		list_del_rcu(&prog->link);
+		tcf_unbind_filter(tp, &prog->res);
 		call_rcu(&prog->rcu, __cls_bpf_delete_prog);
 	}
 
@@ -282,6 +283,7 @@ static int cls_bpf_change(struct net *net, struct sk_buff *in_skb,
 
 	if (oldprog) {
 		list_replace_rcu(&prog->link, &oldprog->link);
+		tcf_unbind_filter(tp, &oldprog->res);
 		call_rcu(&oldprog->rcu, __cls_bpf_delete_prog);
 	} else {
 		list_add_rcu(&prog->link, &head->plist);
diff --git a/net/sched/cls_fw.c b/net/sched/cls_fw.c
index da805ae..dbfdfd1 100644
--- a/net/sched/cls_fw.c
+++ b/net/sched/cls_fw.c
@@ -123,9 +123,7 @@ static int fw_init(struct tcf_proto *tp)
 static void fw_delete_filter(struct rcu_head *head)
 {
 	struct fw_filter *f = container_of(head, struct fw_filter, rcu);
-	struct tcf_proto *tp = f->tp;
 
-	tcf_unbind_filter(tp, &f->res);
 	tcf_exts_destroy(&f->exts);
 	kfree(f);
 }
@@ -143,6 +141,7 @@ static void fw_destroy(struct tcf_proto *tp)
 		while ((f = rtnl_dereference(head->ht[h])) != NULL) {
 			RCU_INIT_POINTER(head->ht[h],
 					 rtnl_dereference(f->next));
+			tcf_unbind_filter(tp, &f->res);
 			call_rcu(&f->rcu, fw_delete_filter);
 		}
 	}
@@ -166,6 +165,7 @@ static int fw_delete(struct tcf_proto *tp, unsigned long arg)
 	     fp = &pfp->next, pfp = rtnl_dereference(*fp)) {
 		if (pfp == f) {
 			RCU_INIT_POINTER(*fp, rtnl_dereference(f->next));
+			tcf_unbind_filter(tp, &f->res);
 			call_rcu(&f->rcu, fw_delete_filter);
 			return 0;
 		}
@@ -280,6 +280,7 @@ static int fw_change(struct net *net, struct sk_buff *in_skb,
 
 		RCU_INIT_POINTER(fnew->next, rtnl_dereference(pfp->next));
 		rcu_assign_pointer(*fp, fnew);
+		tcf_unbind_filter(tp, &f->res);
 		call_rcu(&f->rcu, fw_delete_filter);
 
 		*arg = (unsigned long)fnew;
diff --git a/net/sched/cls_route.c b/net/sched/cls_route.c
index b665aee..6f22baa 100644
--- a/net/sched/cls_route.c
+++ b/net/sched/cls_route.c
@@ -269,9 +269,7 @@ static void
 route4_delete_filter(struct rcu_head *head)
 {
 	struct route4_filter *f = container_of(head, struct route4_filter, rcu);
-	struct tcf_proto *tp = f->tp;
 
-	tcf_unbind_filter(tp, &f->res);
 	tcf_exts_destroy(&f->exts);
 	kfree(f);
 }
@@ -297,6 +295,7 @@ static void route4_destroy(struct tcf_proto *tp)
 
 					next = rtnl_dereference(f->next);
 					RCU_INIT_POINTER(b->ht[h2], next);
+					tcf_unbind_filter(tp, &f->res);
 					call_rcu(&f->rcu, route4_delete_filter);
 				}
 			}
@@ -338,6 +337,7 @@ static int route4_delete(struct tcf_proto *tp, unsigned long arg)
 			route4_reset_fastmap(head);
 
 			/* Delete it */
+			tcf_unbind_filter(tp, &f->res);
 			call_rcu(&f->rcu, route4_delete_filter);
 
 			/* Strip RTNL protected tree */
@@ -545,8 +545,10 @@ static int route4_change(struct net *net, struct sk_buff *in_skb,
 
 	route4_reset_fastmap(head);
 	*arg = (unsigned long)f;
-	if (fold)
+	if (fold) {
+		tcf_unbind_filter(tp, &fold->res);
 		call_rcu(&fold->rcu, route4_delete_filter);
+	}
 	return 0;
 
 errout: