net/sched: act_mirred: validate the control action inside init()

the following script:

 # tc qdisc add dev crash0 clsact
 # tc filter add dev crash0 egress matchall \
 > action mirred ingress mirror dev lo pass
 # tc actions replace action mirred \
 > ingress mirror dev lo goto chain 42 index 90 cookie c1a0c1a0
 # tc actions show action mirred

had the following output:

 Error: Failed to init TC action chain.
 We have an error talking to the kernel
 total acts 1

         action order 0: mirred (Ingress Mirror to device lo) goto chain 42
         index 90 ref 2 bind 1
         cookie c1a0c1a0

Then, the first packet transmitted by crash0 made the kernel crash:

 Mirror/redirect action on
 BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
 #PF error: [normal kernel read fault]
 PGD 0 P4D 0
 Oops: 0000 [#1] SMP PTI
 CPU: 3 PID: 47 Comm: kworker/3:1 Not tainted 5.0.0-rc4.gotochain_crash+ torvalds#533
 Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
 Workqueue: ipv6_addrconf addrconf_dad_work
 RIP: 0010:tcf_action_exec+0xb8/0x100
 Code: 00 00 00 20 74 1d 83 f8 03 75 09 49 83 c4 08 4d 39 ec 75 bc 48 83 c4 10 5b 5d 41 5c 41 5d 41 5e 41 5f c3 49 8b 97 a8 00 00 00 <48> 8b 12 48 89 55 00 48 83 c4 10 5b 5d 41 5c 41 5d 41 5e 41 5f c3
 RSP: 0018:ffffa772404b7ad0 EFLAGS: 00010246
 RAX: 000000002000002a RBX: ffff9c5afc3f4300 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: ffff9c5afdba9380 RDI: 0000000000029380
 RBP: ffffa772404b7b70 R08: ffff9c5af7010028 R09: ffff9c5af7010029
 R10: 0000000000000000 R11: ffff9c5af94c6a38 R12: ffff9c5af7953000
 R13: ffff9c5af7953008 R14: 0000000000000001 R15: ffff9c5af7953d00
 FS:  0000000000000000(0000) GS:ffff9c5afdb80000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000000 CR3: 000000007c514004 CR4: 00000000001606e0
 Call Trace:
  tcf_classify+0x58/0x120
  __dev_queue_xmit+0x40a/0x890
  ? ndisc_next_option+0x50/0x50
  ? ___neigh_create+0x4d5/0x680
  ? ip6_finish_output2+0x1b5/0x590
  ip6_finish_output2+0x1b5/0x590
  ? ip6_output+0x68/0x110
  ip6_output+0x68/0x110
  ? nf_hook.constprop.28+0x79/0xc0
  ndisc_send_skb+0x248/0x2e0
  ndisc_send_ns+0xf8/0x200
  ? addrconf_dad_work+0x389/0x4b0
  addrconf_dad_work+0x389/0x4b0
  ? __switch_to_asm+0x34/0x70
  ? process_one_work+0x195/0x380
  ? addrconf_dad_completed+0x370/0x370
  process_one_work+0x195/0x380
  worker_thread+0x30/0x390
  ? process_one_work+0x380/0x380
  kthread+0x113/0x130
  ? kthread_park+0x90/0x90
  ret_from_fork+0x35/0x40
 Modules linked in: act_mirred veth ip6table_filter ip6_tables iptable_filter binfmt_misc ext4 crct10dif_pclmul snd_hda_codec_generic crc32_pclmul snd_hda_intel snd_hda_codec mbcache ghash_clmulni_intel jbd2 snd_hwdep snd_hda_core snd_seq snd_seq_device snd_pcm aesni_intel snd_timer snd crypto_simd cryptd glue_helper soundcore virtio_balloon joydev pcspkr i2c_piix4 nfsd auth_rpcgss nfs_acl lockd grace sunrpc ip_tables xfs ata_generic pata_acpi qxl drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops virtio_net ttm virtio_blk net_failover virtio_console failover drm ata_piix crc32c_intel virtio_pci serio_raw libata virtio_ring virtio floppy dm_mirror dm_region_hash dm_log dm_mod
 CR2: 0000000000000000

Validating the control action within tcf_mirred_init() proved to fix the
above issue. For the same reason, postpone the assignment of tcfa_action
and tcfm_eaction to avoid partial reconfiguration of a mirred rule when
it's replaced by another one that mirrors to a device that does not
exist. A TDC selftest is added to verify the correct behavior.

Fixes: db50514 ("net: sched: add termination action to allow goto chain")
Fixes: 97763dc ("net_sched: reject unknown tcfa_action values")
Signed-off-by: Davide Caratti <[email protected]>

net/sched/act_mirred.c

@@ -99,6 +99,7 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
 {
 	struct tc_action_net *tn = net_generic(net, mirred_net_id);
 	struct nlattr *tb[TCA_MIRRED_MAX + 1];
+	struct tcf_chain *newchain = NULL, *oldchain;
 	bool mac_header_xmit = false;
 	struct tc_mirred *parm;
 	struct tcf_mirred *m;
@@ -158,18 +159,20 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
 		tcf_idr_release(*a, bind);
 		return -EEXIST;
 	}
+	err = tcf_action_check_ctrlact(parm->action, tp, &newchain, extack);
+	if (err)
+		goto release_idr;
+
 	m = to_mirred(*a);
 
 	spin_lock_bh(&m->tcf_lock);
-	m->tcf_action = parm->action;
-	m->tcfm_eaction = parm->eaction;
 
 	if (parm->ifindex) {
 		dev = dev_get_by_index(net, parm->ifindex);
 		if (!dev) {
 			spin_unlock_bh(&m->tcf_lock);
-			tcf_idr_release(*a, bind);
-			return -ENODEV;
+			err = -ENODEV;
+			goto put_chain;
 		}
 		mac_header_xmit = dev_is_mac_header_xmit(dev);
 		rcu_swap_protected(m->tcfm_dev, dev,
@@ -178,6 +181,10 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
 			dev_put(dev);
 		m->tcfm_mac_header_xmit = mac_header_xmit;
 	}
+	oldchain = m->tcf_goto_chain;
+	m->tcf_goto_chain = newchain;
+	m->tcf_action = parm->action;
+	m->tcfm_eaction = parm->eaction;
 	spin_unlock_bh(&m->tcf_lock);
 
 	if (ret == ACT_P_CREATED) {
@@ -188,7 +195,15 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla,
 		tcf_idr_insert(tn, *a);
 	}
 
+	if (oldchain)
+		tcf_chain_put_by_act(oldchain);
 	return ret;
+put_chain:
+	if (newchain)
+		tcf_chain_put_by_act(newchain);
+release_idr:
+	tcf_idr_release(*a, bind);
+	return err;
 }
 
 static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,

tools/testing/selftests/tc-testing/tc-tests/actions/mirred.json

@@ -434,5 +434,30 @@
         "teardown": [
             "$TC actions flush action mirred"
         ]
+    },
+    {
+        "id": "2a9a",
+        "name": "Replace mirred action with invalid goto chain control",
+        "category": [
+            "actions",
+            "mirred"
+        ],
+        "setup": [
+            [
+                "$TC actions flush action mirred",
+                0,
+                1,
+                255
+            ],
+            "$TC actions add action mirred ingress mirror dev lo drop index 90"
+        ],
+        "cmdUnderTest": "$TC actions replace action mirred ingress mirror dev lo goto chain 42 index 90 cookie c1a0c1a0",
+        "expExitCode": "255",
+        "verifyCmd": "$TC actions get action mirred index 90",
+        "matchPattern": "action order [0-9]*: mirred \\(Ingress Mirror to device lo\\) drop.*index 90 ref",
+        "matchCount": "1",
+        "teardown": [
+            "$TC actions flush action mirred"
+        ]
     }
 ]