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

the following script:

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

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: connmark zone 0 goto chain 42
          index 90 ref 2 bind 1
         cookie c1a0c1a0

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

 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: 0 PID: 302 Comm: kworker/0:2 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:ffff9bea406c3ad0 EFLAGS: 00010246
 RAX: 000000002000002a RBX: ffff8c5dfc009f00 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: ffff9bea406c3a80 RDI: ffff8c5dfb9d6ec0
 RBP: ffff9bea406c3b70 R08: ffff8c5dfda222a0 R09: ffffffff90933c3c
 R10: 0000000000000000 R11: 0000000092793f7d R12: ffff8c5df48b3c00
 R13: ffff8c5df48b3c08 R14: 0000000000000001 R15: ffff8c5dfb9d6e40
 FS:  0000000000000000(0000) GS:ffff8c5dfda00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000000 CR3: 0000000062e0e006 CR4: 00000000001606f0
 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_connmark nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 veth ip6table_filter ip6_tables iptable_filter binfmt_misc ext4 crct10dif_pclmul mbcache crc32_pclmul jbd2 snd_hda_codec_generic ghash_clmulni_intel snd_hda_intel snd_hda_codec snd_hwdep snd_hda_core snd_seq snd_seq_device snd_pcm aesni_intel snd_timer crypto_simd cryptd snd glue_helper joydev virtio_balloon pcspkr soundcore i2c_piix4 nfsd auth_rpcgss nfs_acl lockd grace sunrpc ip_tables xfs ata_generic pata_acpi qxl drm_kms_helper virtio_net net_failover syscopyarea virtio_blk failover virtio_console sysfillrect sysimgblt fb_sys_fops ttm drm ata_piix crc32c_intel serio_raw libata virtio_pci virtio_ring virtio floppy dm_mirror dm_region_hash dm_log dm_mod
 CR2: 0000000000000000

Validating the control action within tcf_connmark_init() proved to fix the
above issue. 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_connmark.c

@@ -21,6 +21,7 @@
 #include <net/netlink.h>
 #include <net/pkt_sched.h>
 #include <net/act_api.h>
+#include <net/pkt_cls.h>
 #include <uapi/linux/tc_act/tc_connmark.h>
 #include <net/tc_act/tc_connmark.h>
 
@@ -101,10 +102,11 @@ static int tcf_connmark_init(struct net *net, struct nlattr *nla,
 			     struct netlink_ext_ack *extack)
 {
 	struct tc_action_net *tn = net_generic(net, connmark_net_id);
+	struct tcf_chain *newchain = NULL, *oldchain;
 	struct nlattr *tb[TCA_CONNMARK_MAX + 1];
 	struct tcf_connmark_info *ci;
 	struct tc_connmark *parm;
-	int ret = 0;
+	int ret = 0, err;
 
 	if (!nla)
 		return -EINVAL;
@@ -129,6 +131,12 @@ static int tcf_connmark_init(struct net *net, struct nlattr *nla,
 		}
 
 		ci = to_connmark(*a);
+		err = tcf_action_check_ctrlact(parm->action, tp, &newchain,
+					       extack);
+		if (err)
+			goto release_idr;
+		oldchain = ci->tcf_goto_chain;
+		ci->tcf_goto_chain = newchain;
 		ci->tcf_action = parm->action;
 		ci->net = net;
 		ci->zone = parm->zone;
@@ -143,15 +151,29 @@ static int tcf_connmark_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;
 		/* replacing action and zone */
 		spin_lock_bh(&ci->tcf_lock);
+		oldchain = ci->tcf_goto_chain;
+		ci->tcf_goto_chain = newchain;
 		ci->tcf_action = parm->action;
 		ci->zone = parm->zone;
 		spin_unlock_bh(&ci->tcf_lock);
 		ret = 0;
+	} else {
+		goto end;
 	}
 
+	if (oldchain)
+		tcf_chain_put_by_act(oldchain);
+end:
 	return ret;
+release_idr:
+	tcf_idr_release(*a, bind);
+	return err;
 }
 
 static inline int tcf_connmark_dump(struct sk_buff *skb, struct tc_action *a,

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

@@ -287,5 +287,30 @@
         "teardown": [
             "$TC actions flush action connmark"
         ]
+    },
+    {
+        "id": "c506",
+        "name": "Replace connmark with invalid goto chain control",
+        "category": [
+            "actions",
+            "connmark"
+        ],
+        "setup": [
+            [
+                "$TC actions flush action connmark",
+                0,
+                1,
+                255
+            ],
+            "$TC actions add action connmark pass index 90"
+        ],
+        "cmdUnderTest": "$TC actions replace action connmark goto chain 42 index 90 cookie c1a0c1a0",
+        "expExitCode": "255",
+        "verifyCmd": "$TC actions get action connmark index 90",
+        "matchPattern": "action order [0-9]+: connmark zone 0 pass.*index 90 ref",
+        "matchCount": "1",
+        "teardown": [
+            "$TC actions flush action connmark"
+        ]
     }
 ]