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

the following script:

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

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: skbedit  ptype host 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: 3 PID: 3467 Comm: kworker/3:3 Not tainted 5.0.0-rc4.gotochain_crash+ torvalds#536
 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:ffffb50a81e1fad0 EFLAGS: 00010246
 RAX: 000000002000002a RBX: ffff9aa47ba4ea00 RCX: 0000000000000001
 RDX: 0000000000000000 RSI: ffff9aa469eeb3c0 RDI: ffff9aa47ba4ea00
 RBP: ffffb50a81e1fb70 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000000000000 R11: ffff9aa47bce0638 R12: ffff9aa4793b0c00
 R13: ffff9aa4793b0c08 R14: 0000000000000001 R15: ffff9aa469eeb3c0
 FS:  0000000000000000(0000) GS:ffff9aa474780000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000000 CR3: 000000007360e005 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_skbedit veth ip6table_filter ip6_tables iptable_filter binfmt_misc crct10dif_pclmul crc32_pclmul ghash_clmulni_intel ext4 snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hwdep mbcache snd_hda_core jbd2 snd_seq snd_seq_device snd_pcm aesni_intel crypto_simd cryptd snd_timer glue_helper snd joydev soundcore pcspkr virtio_balloon 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 ttm virtio_net net_failover drm failover virtio_blk virtio_console ata_piix virtio_pci crc32c_intel serio_raw libata virtio_ring virtio floppy dm_mirror dm_region_hash dm_log dm_mod
 CR2: 0000000000000000

Validating the control action within tcf_skbedit_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]>

Author: dcaratti

net/sched/act_skbedit.c

@@ -26,6 +26,7 @@
 #include <net/ip.h>
 #include <net/ipv6.h>
 #include <net/dsfield.h>
+#include <net/pkt_cls.h>
 
 #include <linux/tc_act/tc_skbedit.h>
 #include <net/tc_act/tc_skbedit.h>
@@ -100,6 +101,7 @@ static int tcf_skbedit_init(struct net *net, struct nlattr *nla,
 			    struct netlink_ext_ack *extack)
 {
 	struct tc_action_net *tn = net_generic(net, skbedit_net_id);
+	struct tcf_chain *newchain = NULL, *oldchain;
 	struct tcf_skbedit_params *params_new;
 	struct nlattr *tb[TCA_SKBEDIT_MAX + 1];
 	struct tc_skbedit *parm;
@@ -187,12 +189,13 @@ static int tcf_skbedit_init(struct net *net, struct nlattr *nla,
 			return -EEXIST;
 		}
 	}
+	err = tcf_action_check_ctrlact(parm->action, tp, &newchain, extack);
+	if (err)
+		goto release_idr;
 
 	params_new = kzalloc(sizeof(*params_new), GFP_KERNEL);
-	if (unlikely(!params_new)) {
-		tcf_idr_release(*a, bind);
-		return -ENOMEM;
-	}
+	if (unlikely(!params_new))
+		goto put_chain;
 
 	params_new->flags = flags;
 	if (flags & SKBEDIT_F_PRIORITY)
@@ -209,6 +212,8 @@ static int tcf_skbedit_init(struct net *net, struct nlattr *nla,
 		params_new->mask = *mask;
 
 	spin_lock_bh(&d->tcf_lock);
+	oldchain = d->tcf_goto_chain;
+	d->tcf_goto_chain = newchain;
 	d->tcf_action = parm->action;
 	rcu_swap_protected(d->params, params_new,
 			   lockdep_is_held(&d->tcf_lock));
@@ -218,7 +223,16 @@ static int tcf_skbedit_init(struct net *net, struct nlattr *nla,
 
 	if (ret == ACT_P_CREATED)
 		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_skbedit_dump(struct sk_buff *skb, struct tc_action *a,

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

@@ -484,5 +484,30 @@
         "teardown": [
             "$TC actions flush action skbedit"
         ]
+    },
+    {
+        "id": "1b2b",
+        "name": "Replace skbedit action with invalid goto_chain control",
+        "category": [
+            "actions",
+            "skbedit"
+        ],
+        "setup": [
+            [
+                "$TC actions flush action skbedit",
+                0,
+                1,
+                255
+            ],
+            "$TC actions add action skbedit ptype host pass index 90"
+        ],
+        "cmdUnderTest": "$TC actions replace action skbedit ptype host goto chain 42 index 90 cookie c1a0c1a0",
+        "expExitCode": "255",
+        "verifyCmd": "$TC actions list action skbedit",
+        "matchPattern": "action order [0-9]*: skbedit  ptype host pass.*index 90 ref",
+        "matchCount": "1",
+        "teardown": [
+            "$TC actions flush action skbedit"
+        ]
     }
 ]