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

the following script:

 # tc qdisc add dev crash0 clsact
 # tc filter add dev crash0 egress matchall \
 > action skbmod set smac 00:c1:a0:c1:a0:00 pass index 90
 # tc actions replace action skbmod \
 > set smac 00:c1:a0:c1:a0:00 goto chain 42 index 90 cookie c1a0c1a0
 # tc actions show action skbmod

had the following output:

 src MAC address <00:c1:a0:c1:a0:00>
 src MAC address <00:c1:a0:c1:a0:00>
 Error: Failed to init TC action chain.
 We have an error talking to the kernel
 total acts 1

         action order 0: skbmod goto chain 42 set smac 00:c1:a0:c1:a0:00
          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 800000002d5c7067 P4D 800000002d5c7067 PUD 77e16067 PMD 0
 Oops: 0000 [#1] SMP PTI
 CPU: 3 PID: 0 Comm: swapper/3 Not tainted 5.0.0-rc4.gotochain_crash+ #536
 Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
 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:ffff8987ffd83be0 EFLAGS: 00010246
 RAX: 000000002000002a RBX: ffff8987aeb68800 RCX: ffff8987fa263640
 RDX: 0000000000000000 RSI: ffff8987f51c8802 RDI: 00000000000000a0
 RBP: ffff8987ffd83c80 R08: ffff8987f939bac8 R09: 0000000000000000
 R10: 0000000000000000 R11: 0000000000000000 R12: ffff8987f5c77d00
 R13: ffff8987f5c77d08 R14: 0000000000000001 R15: ffff8987f0c29f00
 FS:  0000000000000000(0000) GS:ffff8987ffd80000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000000 CR3: 000000007832c004 CR4: 00000000001606e0
 Call Trace:
  <IRQ>
  tcf_classify+0x58/0x120
  __dev_queue_xmit+0x40a/0x890
  ? ip6_finish_output2+0x369/0x590
  ip6_finish_output2+0x369/0x590
  ? ip6_output+0x68/0x110
  ip6_output+0x68/0x110
  ? nf_hook.constprop.35+0x79/0xc0
  mld_sendpack+0x16f/0x220
  mld_ifc_timer_expire+0x195/0x2c0
  ? igmp6_timer_handler+0x70/0x70
  call_timer_fn+0x2b/0x130
  run_timer_softirq+0x3e8/0x440
  ? tick_sched_timer+0x37/0x70
  __do_softirq+0xe3/0x2f5
  irq_exit+0xf0/0x100
  smp_apic_timer_interrupt+0x6c/0x130
  apic_timer_interrupt+0xf/0x20
  </IRQ>
 RIP: 0010:native_safe_halt+0x2/0x10
 Code: 56 ff ff ff 7f f3 c3 65 48 8b 04 25 00 5c 01 00 f0 80 48 02 20 48 8b 00 a8 08 74 8b eb c1 90 90 90 90 90 90 90 90 90 90 fb f4 <c3> 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 f4 c3 90 90 90 90 90 90
 RSP: 0018:ffffa2a1c038feb8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
 RAX: ffffffffa94184f0 RBX: 0000000000000003 RCX: 0000000000000001
 RDX: 0000000000000001 RSI: 0000000000000087 RDI: 0000000000000003
 RBP: 0000000000000003 R08: 001123cfc2ba71ac R09: 0000000000000000
 R10: 0000000000000000 R11: 00000000000f4240 R12: 0000000000000000
 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
  ? __sched_text_end+0x1/0x1
  default_idle+0x1c/0x140
  do_idle+0x1c4/0x280
  cpu_startup_entry+0x19/0x20
  start_secondary+0x1a7/0x200
  secondary_startup_64+0xa4/0xb0
 Modules linked in: act_skbmod veth ip6table_filter ip6_tables iptable_filter binfmt_misc ext4 crct10dif_pclmul crc32_pclmul ghash_clmulni_intel mbcache jbd2 snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hwdep snd_hda_core snd_seq snd_seq_device aesni_intel crypto_simd cryptd glue_helper snd_pcm joydev pcspkr virtio_balloon snd_timer snd i2c_piix4 soundcore nfsd auth_rpcgss nfs_acl lockd grace sunrpc ip_tables xfs ata_generic pata_acpi qxl drm_kms_helper syscopyarea sysfillrect virtio_net sysimgblt fb_sys_fops net_failover virtio_console ttm virtio_blk failover drm crc32c_intel serio_raw ata_piix virtio_pci libata virtio_ring virtio floppy dm_mirror dm_region_hash dm_log dm_mod
 CR2: 0000000000000000

Validating the control action within tcf_skbmod_init() proved to fix the
above issue. A TDC selftest is added to verify the correct behavior.

Fixes: db50514f ("net: sched: add termination action to allow goto chain")
Fixes: 97763dc0 ("net_sched: reject unknown tcfa_action values")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_skbmod.c

@@ -16,6 +16,7 @@
 #include <linux/rtnetlink.h>
 #include <net/netlink.h>
 #include <net/pkt_sched.h>
+#include <net/pkt_cls.h>
 
 #include <linux/tc_act/tc_skbmod.h>
 #include <net/tc_act/tc_skbmod.h>
@@ -88,6 +89,7 @@ static int tcf_skbmod_init(struct net *net, struct nlattr *nla,
 	struct tc_action_net *tn = net_generic(net, skbmod_net_id);
 	struct nlattr *tb[TCA_SKBMOD_MAX + 1];
 	struct tcf_skbmod_params *p, *p_old;
+	struct tcf_chain *goto_ch = NULL;
 	struct tc_skbmod *parm;
 	struct tcf_skbmod *d;
 	bool exists = false;
@@ -154,21 +156,24 @@ static int tcf_skbmod_init(struct net *net, struct nlattr *nla,
 		tcf_idr_release(*a, bind);
 		return -EEXIST;
 	}
+	err = tcf_action_check_ctrlact(parm->action, tp, &goto_ch, extack);
+	if (err < 0)
+		goto release_idr;
 
 	d = to_skbmod(*a);
 
 	p = kzalloc(sizeof(struct tcf_skbmod_params), GFP_KERNEL);
 	if (unlikely(!p)) {
-		tcf_idr_release(*a, bind);
-		return -ENOMEM;
+		err = -ENOMEM;
+		goto put_chain;
 	}
 
 	p->flags = lflags;
-	d->tcf_action = parm->action;
 
 	if (ovr)
 		spin_lock_bh(&d->tcf_lock);
 	/* Protected by tcf_lock if overwriting existing action. */
+	goto_ch = tcf_action_set_ctrlact(*a, parm->action, goto_ch);
 	p_old = rcu_dereference_protected(d->skbmod_p, 1);
 
 	if (lflags & SKBMOD_F_DMAC)
@@ -184,10 +189,18 @@ static int tcf_skbmod_init(struct net *net, struct nlattr *nla,
 
 	if (p_old)
 		kfree_rcu(p_old, rcu);
+	if (goto_ch)
+		tcf_chain_put_by_act(goto_ch);
 
 	if (ret == ACT_P_CREATED)
 		tcf_idr_insert(tn, *a);
 	return ret;
+put_chain:
+	if (goto_ch)
+		tcf_chain_put_by_act(goto_ch);
+release_idr:
+	tcf_idr_release(*a, bind);
+	return err;
 }
 
 static void tcf_skbmod_cleanup(struct tc_action *a)

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

@@ -392,5 +392,30 @@
         "teardown": [
             "$TC actions flush action skbmod"
         ]
+    },
+    {
+        "id": "b651",
+        "name": "Replace skbmod action with invalid goto_chain control",
+        "category": [
+            "actions",
+            "skbmod"
+        ],
+        "setup": [
+            [
+                "$TC actions flush action skbmod",
+                0,
+                1,
+                255
+            ],
+            "$TC actions add action skbmod set etype 0x1111 pass index 90"
+        ],
+        "cmdUnderTest": "$TC actions replace action skbmod set etype 0x1111 goto chain 42 index 90 cookie c1a0c1a0",
+        "expExitCode": "255",
+        "verifyCmd": "$TC actions ls action skbmod",
+        "matchPattern": "action order [0-9]*: skbmod pass set etype 0x1111\\s+index 90 ref",
+        "matchCount": "1",
+        "teardown": [
+            "$TC actions flush action skbmod"
+        ]
     }
 ]