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: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>