act_bpf: fix memory leaks when replacing bpf programs

We currently trigger multiple memory leaks when replacing bpf
actions, besides others:

  comm "tc", pid 1909, jiffies 4294851310 (age 1602.796s)
  hex dump (first 32 bytes):
    01 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00  ................
    18 b0 98 6d 00 88 ff ff 00 00 00 00 00 00 00 00  ...m............
  backtrace:
    [<ffffffff817e623e>] kmemleak_alloc+0x4e/0xb0
    [<ffffffff8120a22d>] __vmalloc_node_range+0x1bd/0x2c0
    [<ffffffff8120a37a>] __vmalloc+0x4a/0x50
    [<ffffffff811a8d0a>] bpf_prog_alloc+0x3a/0xa0
    [<ffffffff816c0684>] bpf_prog_create+0x44/0xa0
    [<ffffffffa09ba4eb>] tcf_bpf_init+0x28b/0x3c0 [act_bpf]
    [<ffffffff816d7001>] tcf_action_init_1+0x191/0x1b0
    [<ffffffff816d70a2>] tcf_action_init+0x82/0xf0
    [<ffffffff816d4d12>] tcf_exts_validate+0xb2/0xc0
    [<ffffffffa09b5838>] cls_bpf_modify_existing+0x98/0x340 [cls_bpf]
    [<ffffffffa09b5cd6>] cls_bpf_change+0x1a6/0x274 [cls_bpf]
    [<ffffffff816d56e5>] tc_ctl_tfilter+0x335/0x910
    [<ffffffff816b9145>] rtnetlink_rcv_msg+0x95/0x240
    [<ffffffff816df34f>] netlink_rcv_skb+0xaf/0xc0
    [<ffffffff816b909e>] rtnetlink_rcv+0x2e/0x40
    [<ffffffff816deaaf>] netlink_unicast+0xef/0x1b0

Issue is that the old content from tcf_bpf is allocated and needs
to be released when we replace it. We seem to do that since the
beginning of act_bpf on the filter and insns, later on the name as
well.

Example test case, after patch:

  # FOO="1,6 0 0 4294967295,"
  # BAR="1,6 0 0 4294967294,"
  # tc actions add action bpf bytecode "$FOO" index 2
  # tc actions show action bpf
   action order 0: bpf bytecode '1,6 0 0 4294967295' default-action pipe
   index 2 ref 1 bind 0
  # tc actions replace action bpf bytecode "$BAR" index 2
  # tc actions show action bpf
   action order 0: bpf bytecode '1,6 0 0 4294967294' default-action pipe
   index 2 ref 1 bind 0
  # tc actions replace action bpf bytecode "$FOO" index 2
  # tc actions show action bpf
   action order 0: bpf bytecode '1,6 0 0 4294967295' default-action pipe
   index 2 ref 1 bind 0
  # tc actions del action bpf index 2
  [...]
  # echo "scan" > /sys/kernel/debug/kmemleak
  # cat /sys/kernel/debug/kmemleak | grep "comm \"tc\"" | wc -l
  0

Fixes: d23b8ad8 ("tc: add BPF based action")
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/act_bpf.c

@@ -27,9 +27,10 @@
 struct tcf_bpf_cfg {
 	struct bpf_prog *filter;
 	struct sock_filter *bpf_ops;
-	char *bpf_name;
+	const char *bpf_name;
 	u32 bpf_fd;
 	u16 bpf_num_ops;
+	bool is_ebpf;
 };
 
 static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
@@ -207,6 +208,7 @@ static int tcf_bpf_init_from_ops(struct nlattr **tb, struct tcf_bpf_cfg *cfg)
 	cfg->bpf_ops = bpf_ops;
 	cfg->bpf_num_ops = bpf_num_ops;
 	cfg->filter = fp;
+	cfg->is_ebpf = false;
 
 	return 0;
 }
@@ -241,18 +243,40 @@ static int tcf_bpf_init_from_efd(struct nlattr **tb, struct tcf_bpf_cfg *cfg)
 	cfg->bpf_fd = bpf_fd;
 	cfg->bpf_name = name;
 	cfg->filter = fp;
+	cfg->is_ebpf = true;
 
 	return 0;
 }
 
+static void tcf_bpf_cfg_cleanup(const struct tcf_bpf_cfg *cfg)
+{
+	if (cfg->is_ebpf)
+		bpf_prog_put(cfg->filter);
+	else
+		bpf_prog_destroy(cfg->filter);
+
+	kfree(cfg->bpf_ops);
+	kfree(cfg->bpf_name);
+}
+
+static void tcf_bpf_prog_fill_cfg(const struct tcf_bpf *prog,
+				  struct tcf_bpf_cfg *cfg)
+{
+	cfg->is_ebpf = tcf_bpf_is_ebpf(prog);
+	cfg->filter = prog->filter;
+
+	cfg->bpf_ops = prog->bpf_ops;
+	cfg->bpf_name = prog->bpf_name;
+}
+
 static int tcf_bpf_init(struct net *net, struct nlattr *nla,
 			struct nlattr *est, struct tc_action *act,
 			int replace, int bind)
 {
 	struct nlattr *tb[TCA_ACT_BPF_MAX + 1];
+	struct tcf_bpf_cfg cfg, old;
 	struct tc_act_bpf *parm;
 	struct tcf_bpf *prog;
-	struct tcf_bpf_cfg cfg;
 	bool is_bpf, is_ebpf;
 	int ret;
 
@@ -301,6 +325,9 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
 	prog = to_bpf(act);
 	spin_lock_bh(&prog->tcf_lock);
 
+	if (ret != ACT_P_CREATED)
+		tcf_bpf_prog_fill_cfg(prog, &old);
+
 	prog->bpf_ops = cfg.bpf_ops;
 	prog->bpf_name = cfg.bpf_name;
 
@@ -316,32 +343,22 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
 
 	if (ret == ACT_P_CREATED)
 		tcf_hash_insert(act);
+	else
+		tcf_bpf_cfg_cleanup(&old);
 
 	return ret;
 
 destroy_fp:
-	if (is_ebpf)
-		bpf_prog_put(cfg.filter);
-	else
-		bpf_prog_destroy(cfg.filter);
-
-	kfree(cfg.bpf_ops);
-	kfree(cfg.bpf_name);
-
+	tcf_bpf_cfg_cleanup(&cfg);
 	return ret;
 }
 
 static void tcf_bpf_cleanup(struct tc_action *act, int bind)
 {
-	const struct tcf_bpf *prog = act->priv;
-
-	if (tcf_bpf_is_ebpf(prog))
-		bpf_prog_put(prog->filter);
-	else
-		bpf_prog_destroy(prog->filter);
+	struct tcf_bpf_cfg tmp;
 
-	kfree(prog->bpf_ops);
-	kfree(prog->bpf_name);
+	tcf_bpf_prog_fill_cfg(act->priv, &tmp);
+	tcf_bpf_cfg_cleanup(&tmp);
 }
 
 static struct tc_action_ops act_bpf_ops __read_mostly = {