net/sched: fix NULL dereference in the error path of tcf_bpf_init()

when tcf_bpf_init_from_ops() fails (e.g. because of program having invalid
number of instructions), tcf_bpf_cfg_cleanup() calls bpf_prog_put(NULL) or
bpf_prog_destroy(NULL). Unless CONFIG_BPF_SYSCALL is unset, this causes
the following error:

 BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
 PGD 800000007345a067 P4D 800000007345a067 PUD 340e1067 PMD 0
 Oops: 0000 [#1] SMP PTI
 Modules linked in: act_bpf(E) ip6table_filter ip6_tables iptable_filter binfmt_misc ext4 mbcache jbd2 crct10dif_pclmul crc32_pclmul ghash_clmulni_intel snd_hda_codec_generic pcbc snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device snd_pcm aesni_intel crypto_simd glue_helper cryptd joydev snd_timer snd virtio_balloon pcspkr soundcore i2c_piix4 nfsd auth_rpcgss nfs_acl lockd grace sunrpc ip_tables xfs libcrc32c ata_generic pata_acpi qxl drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm virtio_blk drm virtio_net virtio_console i2c_core crc32c_intel serio_raw virtio_pci ata_piix libata virtio_ring floppy virtio dm_mirror dm_region_hash dm_log dm_mod [last unloaded: act_bpf]
 CPU: 3 PID: 5654 Comm: tc Tainted: G            E    4.16.0.bpf_test+ #408
 Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
 RIP: 0010:__bpf_prog_put+0xc/0xc0
 RSP: 0018:ffff9594003ef728 EFLAGS: 00010202
 RAX: 0000000000000000 RBX: ffff9594003ef758 RCX: 0000000000000024
 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
 RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000044
 R10: 0000000000000220 R11: ffff8a7ab9f17131 R12: 0000000000000000
 R13: ffff8a7ab7c3c8e0 R14: 0000000000000001 R15: ffff8a7ab88f1054
 FS:  00007fcb2f17c740(0000) GS:ffff8a7abfd80000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000020 CR3: 000000007c888006 CR4: 00000000001606e0
 Call Trace:
  tcf_bpf_cfg_cleanup+0x2f/0x40 [act_bpf]
  tcf_bpf_cleanup+0x4c/0x70 [act_bpf]
  __tcf_idr_release+0x79/0x140
  tcf_bpf_init+0x125/0x330 [act_bpf]
  tcf_action_init_1+0x2cc/0x430
  ? get_page_from_freelist+0x3f0/0x11b0
  tcf_action_init+0xd3/0x1b0
  tc_ctl_action+0x18b/0x240
  rtnetlink_rcv_msg+0x29c/0x310
  ? _cond_resched+0x15/0x30
  ? __kmalloc_node_track_caller+0x1b9/0x270
  ? rtnl_calcit.isra.29+0x100/0x100
  netlink_rcv_skb+0xd2/0x110
  netlink_unicast+0x17c/0x230
  netlink_sendmsg+0x2cd/0x3c0
  sock_sendmsg+0x30/0x40
  ___sys_sendmsg+0x27a/0x290
  ? mem_cgroup_commit_charge+0x80/0x130
  ? page_add_new_anon_rmap+0x73/0xc0
  ? do_anonymous_page+0x2a2/0x560
  ? __handle_mm_fault+0xc75/0xe20
  __sys_sendmsg+0x58/0xa0
  do_syscall_64+0x6e/0x1a0
  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
 RIP: 0033:0x7fcb2e58eba0
 RSP: 002b:00007ffc93c496c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
 RAX: ffffffffffffffda RBX: 00007ffc93c497f0 RCX: 00007fcb2e58eba0
 RDX: 0000000000000000 RSI: 00007ffc93c49740 RDI: 0000000000000003
 RBP: 000000005ac6a646 R08: 0000000000000002 R09: 0000000000000000
 R10: 00007ffc93c49120 R11: 0000000000000246 R12: 0000000000000000
 R13: 00007ffc93c49804 R14: 0000000000000001 R15: 000000000066afa0
 Code: 5f 00 48 8b 43 20 48 c7 c7 70 2f 7c b8 c7 40 10 00 00 00 00 5b e9 a5 8b 61 00 0f 1f 44 00 00 0f 1f 44 00 00 41 54 55 48 89 fd 53 <48> 8b 47 20 f0 ff 08 74 05 5b 5d 41 5c c3 41 89 f4 0f 1f 44 00
 RIP: __bpf_prog_put+0xc/0xc0 RSP: ffff9594003ef728
 CR2: 0000000000000020

Fix it in tcf_bpf_cfg_cleanup(), ensuring that bpf_prog_{put,destroy}(f)
is called only when f is not NULL.

Fixes: bbc09e78 ("net/sched: fix idr leak on the error path of tcf_bpf_init()")
Reported-by: Lucas Bates <lucasb@mojatatu.com>
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_bpf.c

@@ -248,10 +248,14 @@ static int tcf_bpf_init_from_efd(struct nlattr **tb, struct tcf_bpf_cfg *cfg)
 
 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);
+	struct bpf_prog *filter = cfg->filter;
+
+	if (filter) {
+		if (cfg->is_ebpf)
+			bpf_prog_put(filter);
+		else
+			bpf_prog_destroy(filter);
+	}
 
 	kfree(cfg->bpf_ops);
 	kfree(cfg->bpf_name);