Re: [PATCH v2] tun: fix use-after-free when register netdev failed

[Jason Wang <jasowang@redhat.com>]

On 2019/8/16 下午7:00, Yang Yingliang wrote:
> I got a UAF repport in tun driver when doing fuzzy test:
>
> [  466.269490] ==================================================================
> [  466.271792] BUG: KASAN: use-after-free in tun_chr_read_iter+0x2ca/0x2d0
> [  466.271806] Read of size 8 at addr ffff888372139250 by task tun-test/2699
> [  466.271810]
> [  466.271824] CPU: 1 PID: 2699 Comm: tun-test Not tainted 5.3.0-rc1-00001-g5a9433db2614-dirty #427
> [  466.271833] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
> [  466.271838] Call Trace:
> [  466.271858]  dump_stack+0xca/0x13e
> [  466.271871]  ? tun_chr_read_iter+0x2ca/0x2d0
> [  466.271890]  print_address_description+0x79/0x440
> [  466.271906]  ? vprintk_func+0x5e/0xf0
> [  466.271920]  ? tun_chr_read_iter+0x2ca/0x2d0
> [  466.271935]  __kasan_report+0x15c/0x1df
> [  466.271958]  ? tun_chr_read_iter+0x2ca/0x2d0
> [  466.271976]  kasan_report+0xe/0x20
> [  466.271987]  tun_chr_read_iter+0x2ca/0x2d0
> [  466.272013]  do_iter_readv_writev+0x4b7/0x740
> [  466.272032]  ? default_llseek+0x2d0/0x2d0
> [  466.272072]  do_iter_read+0x1c5/0x5e0
> [  466.272110]  vfs_readv+0x108/0x180
> [  466.299007]  ? compat_rw_copy_check_uvector+0x440/0x440
> [  466.299020]  ? fsnotify+0x888/0xd50
> [  466.299040]  ? __fsnotify_parent+0xd0/0x350
> [  466.299064]  ? fsnotify_first_mark+0x1e0/0x1e0
> [  466.304548]  ? vfs_write+0x264/0x510
> [  466.304569]  ? ksys_write+0x101/0x210
> [  466.304591]  ? do_preadv+0x116/0x1a0
> [  466.304609]  do_preadv+0x116/0x1a0
> [  466.309829]  do_syscall_64+0xc8/0x600
> [  466.309849]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [  466.309861] RIP: 0033:0x4560f9
> [  466.309875] Code: 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> [  466.309889] RSP: 002b:00007ffffa5166e8 EFLAGS: 00000206 ORIG_RAX: 0000000000000127
> [  466.322992] RAX: ffffffffffffffda RBX: 0000000000400460 RCX: 00000000004560f9
> [  466.322999] RDX: 0000000000000003 RSI: 00000000200008c0 RDI: 0000000000000003
> [  466.323007] RBP: 00007ffffa516700 R08: 0000000000000004 R09: 0000000000000000
> [  466.323014] R10: 0000000000000000 R11: 0000000000000206 R12: 000000000040cb10
> [  466.323021] R13: 0000000000000000 R14: 00000000006d7018 R15: 0000000000000000
> [  466.323057]
> [  466.323064] Allocated by task 2605:
> [  466.335165]  save_stack+0x19/0x80
> [  466.336240]  __kasan_kmalloc.constprop.8+0xa0/0xd0
> [  466.337755]  kmem_cache_alloc+0xe8/0x320
> [  466.339050]  getname_flags+0xca/0x560
> [  466.340229]  user_path_at_empty+0x2c/0x50
> [  466.341508]  vfs_statx+0xe6/0x190
> [  466.342619]  __do_sys_newstat+0x81/0x100
> [  466.343908]  do_syscall_64+0xc8/0x600
> [  466.345303]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [  466.347034]
> [  466.347517] Freed by task 2605:
> [  466.348471]  save_stack+0x19/0x80
> [  466.349476]  __kasan_slab_free+0x12e/0x180
> [  466.350726]  kmem_cache_free+0xc8/0x430
> [  466.351874]  putname+0xe2/0x120
> [  466.352921]  filename_lookup+0x257/0x3e0
> [  466.354319]  vfs_statx+0xe6/0x190
> [  466.355498]  __do_sys_newstat+0x81/0x100
> [  466.356889]  do_syscall_64+0xc8/0x600
> [  466.358037]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [  466.359567]
> [  466.360050] The buggy address belongs to the object at ffff888372139100
> [  466.360050]  which belongs to the cache names_cache of size 4096
> [  466.363735] The buggy address is located 336 bytes inside of
> [  466.363735]  4096-byte region [ffff888372139100, ffff88837213a100)
> [  466.367179] The buggy address belongs to the page:
> [  466.368604] page:ffffea000dc84e00 refcount:1 mapcount:0 mapping:ffff8883df1b4f00 index:0x0 compound_mapcount: 0
> [  466.371582] flags: 0x2fffff80010200(slab|head)
> [  466.372910] raw: 002fffff80010200 dead000000000100 dead000000000122 ffff8883df1b4f00
> [  466.375209] raw: 0000000000000000 0000000000070007 00000001ffffffff 0000000000000000
> [  466.377778] page dumped because: kasan: bad access detected
> [  466.379730]
> [  466.380288] Memory state around the buggy address:
> [  466.381844]  ffff888372139100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  466.384009]  ffff888372139180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  466.386131] >ffff888372139200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  466.388257]                                                  ^
> [  466.390234]  ffff888372139280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  466.392512]  ffff888372139300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [  466.394667] ==================================================================
>
> tun_chr_read_iter() accessed the memory which freed by free_netdev()
> called by tun_set_iff():
>
>         CPUA                                     CPUB
>     tun_set_iff()
>       alloc_netdev_mqs()
>       tun_attach()
>                                             tun_chr_read_iter()
>                                               tun_get()
>       register_netdevice() <-- inject error
>       tun_detach_all()
>         synchronize_net()
>                                               tun_do_read()
>                                                 tun_ring_recv()
>                                                   schedule()
>       free_netdev()
>         netdev_freemem()
>                                               tun_put()
>                                                 dev_put() <-- UAF
>
> Move tun_set_real_num_queues() out of tun_attach() and call it
> before register_netdevice() in tun_set_iff().
>
> Call tun_attach() after register_netdevice() to make sure tfile->tun
> is not published until the netdevice is registered. So the read/write
> thread can not use the tun pointer that may freed by free_netdev().
> (The tun and dev pointer are allocated by alloc_netdev_mqs(), they can
> be freed by netdev_freemem().)
>
> ---
> Changes in v2:
>  - add a param in tun_set_real_num_queues()
>  - move tun_set_real_num_queues() out of tun_attach()
>  - call tun_set_real_num_queues() before register_netdevice()
>  - call tun_attach() after register_netdevice()
> ---
>
> Cc: Yang Yingliang <yangyingliang@huawei.com>
> Fixes: eb0fb363f920 ("tuntap: attach queue 0 before registering netdevice")
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Suggested-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
> ---
>  drivers/net/tun.c | 38 +++++++++++++++++++++-----------------
>  1 file changed, 21 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index db16d7a13e00..a19f864c5f8d 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -626,10 +626,11 @@ static inline bool tun_not_capable(struct tun_struct *tun)
>  		!ns_capable(net->user_ns, CAP_NET_ADMIN);
>  }
>  
> -static void tun_set_real_num_queues(struct tun_struct *tun)
> +static void tun_set_real_num_queues(struct tun_struct *tun,
> +				    unsigned int numqueues)
>  {
> -	netif_set_real_num_tx_queues(tun->dev, tun->numqueues);
> -	netif_set_real_num_rx_queues(tun->dev, tun->numqueues);
> +	netif_set_real_num_tx_queues(tun->dev, numqueues);
> +	netif_set_real_num_rx_queues(tun->dev, numqueues);
>  }
>  
>  static void tun_disable_queue(struct tun_struct *tun, struct tun_file *tfile)
> @@ -708,7 +709,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
>  		tun_flow_delete_by_queue(tun, tun->numqueues + 1);
>  		/* Drop read queue */
>  		tun_queue_purge(tfile);
> -		tun_set_real_num_queues(tun);
> +		tun_set_real_num_queues(tun, tun->numqueues);
>  	} else if (tfile->detached && clean) {
>  		tun = tun_enable_queue(tfile);
>  		sock_put(&tfile->sk);
> @@ -873,7 +874,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file,
>  	rcu_assign_pointer(tfile->tun, tun);
>  	rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile);
>  	tun->numqueues++;
> -	tun_set_real_num_queues(tun);
>  out:
>  	return err;
>  }
> @@ -2734,6 +2734,8 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>  		if (err < 0)
>  			return err;
>  
> +		tun_set_real_num_queues(tun, tun->numqueues);
> +
>  		if (tun->flags & IFF_MULTI_QUEUE &&
>  		    (tun->numqueues + tun->numdisabled > 1)) {
>  			/* One or more queue has already been attached, no need
> @@ -2828,14 +2830,18 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>  			      (ifr->ifr_flags & TUN_FEATURES);
>  
>  		INIT_LIST_HEAD(&tun->disabled);
> -		err = tun_attach(tun, file, false, ifr->ifr_flags & IFF_NAPI,
> -				 ifr->ifr_flags & IFF_NAPI_FRAGS);
> -		if (err < 0)
> -			goto err_free_flow;
> +
> +		tun_set_real_num_queues(tun, tun->numqueues + 1);


This looks tricky, why not simply call netif_set_real_num_tx/rx_queues()
here?

Thanks


>  
>  		err = register_netdevice(tun->dev);
>  		if (err < 0)
> -			goto err_detach;
> +			/* register_netdevice() already called tun_free_netdev() */
> +			goto err_free_dev;
> +
> +		err = tun_attach(tun, file, false, ifr->ifr_flags & IFF_NAPI,
> +				 ifr->ifr_flags & IFF_NAPI_FRAGS);
> +		if (err < 0)
> +			goto err_unregister;
>  	}
>  
>  	netif_carrier_on(tun->dev);
> @@ -2851,14 +2857,10 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>  	strcpy(ifr->ifr_name, tun->dev->name);
>  	return 0;
>  
> -err_detach:
> -	tun_detach_all(dev);
> -	/* register_netdevice() already called tun_free_netdev() */
> -	goto err_free_dev;
> +err_unregister:
> +	unregister_netdevice(dev);
> +	return err;
>  
> -err_free_flow:
> -	tun_flow_uninit(tun);
> -	security_tun_dev_free_security(tun->security);
>  err_free_stat:
>  	free_percpu(tun->pcpu_stats);
>  err_free_dev:
> @@ -2979,6 +2981,8 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr)
>  			goto unlock;
>  		ret = tun_attach(tun, file, false, tun->flags & IFF_NAPI,
>  				 tun->flags & IFF_NAPI_FRAGS);
> +		if (!ret)
> +			tun_set_real_num_queues(tun, tun->numqueues);
>  	} else if (ifr->ifr_flags & IFF_DETACH_QUEUE) {
>  		tun = rtnl_dereference(tfile->tun);
>  		if (!tun || !(tun->flags & IFF_MULTI_QUEUE) || tfile->detached)