Subject: Re: [PATCH net 07/16] net/sched: act_connmark: validate the control action inside init()

From: Vlad Buslov <[email-masked]>
Date: Fri, 1 Mar 2019 16:35:55 +0000

On Wed 27 Feb 2019 at 17:40, Davide Caratti <[email-masked]> wrote:
> 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+ #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: db50514f9a9c ("net: sched: add termination action to allow goto chain")
> Fixes: 97763dc0f401 ("net_sched: reject unknown tcfa_action values")
> Signed-off-by: Davide Caratti <[email-masked]>
> ---
>  net/sched/act_connmark.c                      | 24 +++++++++++++++++-
>  .../tc-testing/tc-tests/actions/connmark.json | 25 +++++++++++++++++++
>  2 files changed, 48 insertions(+), 1 deletion(-)
>
> diff --git a/net/sched/act_connmark.c b/net/sched/act_connmark.c
> index 30c4c109c80c..5e02f9f6850a 100644
> --- a/net/sched/act_connmark.c
> +++ b/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;

Maybe just initialize oldchain to NULL to avoid this goto?

>  	}
>  
> +	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,
> diff --git a/tools/testing/selftests/tc-testing/tc-tests/actions/connmark.json b/tools/testing/selftests/tc-testing/tc-tests/actions/connmark.json
> index 13147a1f5731..cadde8f41fcd 100644
> --- a/tools/testing/selftests/tc-testing/tc-tests/actions/connmark.json
> +++ b/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"
> +        ]
>      }
>  ]