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Date: Thu, 15 Aug 2019 17:21:27 +0800
From: Jason Wang <jasowang@...hat.com>
To: Yang Yingliang <yangyingliang@...wei.com>, netdev@...r.kernel.org
Cc: xiyou.wangcong@...il.com, davem@...emloft.net
Subject: Re: [PATCH] tun: fix use-after-free when register netdev failed
On 2019/8/15 下午4:18, 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()
> tun_detach_all()
> synchronize_net()
> tun_do_read()
> tun_ring_recv()
> schedule()
> free_netdev()
> tun_put() <-- UAF
>
> Set a new bit in tun->flag if register_netdevice() successed,
> without this bit, tun_get() returns NULL to avoid using a
> freed tun pointer.
Good catch.
Some comments inline.
>
> Fixes: eb0fb363f920 ("tuntap: attach queue 0 before registering netdevice")
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
> ---
> drivers/net/tun.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index db16d7a13e00..cbd60c276c40 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -115,6 +115,7 @@ do { \
> /* High bits in flags field are unused. */
> #define TUN_VNET_LE 0x80000000
> #define TUN_VNET_BE 0x40000000
> +#define TUN_DEV_REGISTERED 0x20000000
>
> #define TUN_FEATURES (IFF_NO_PI | IFF_ONE_QUEUE | IFF_VNET_HDR | \
> IFF_MULTI_QUEUE | IFF_NAPI | IFF_NAPI_FRAGS)
> @@ -719,8 +720,10 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
> netif_carrier_off(tun->dev);
>
> if (!(tun->flags & IFF_PERSIST) &&
> - tun->dev->reg_state == NETREG_REGISTERED)
> + tun->dev->reg_state == NETREG_REGISTERED) {
> unregister_netdevice(tun->dev);
> + tun->flags &= ~TUN_DEV_REGISTERED;
> + }
> }
> if (tun)
> xdp_rxq_info_unreg(&tfile->xdp_rxq);
> @@ -884,8 +887,10 @@ static struct tun_struct *tun_get(struct tun_file *tfile)
>
> rcu_read_lock();
> tun = rcu_dereference(tfile->tun);
> - if (tun)
> + if (tun && (tun->flags & TUN_DEV_REGISTERED))
> dev_hold(tun->dev);
> + else
> + tun = NULL;
> rcu_read_unlock();
>
> return tun;
> @@ -2836,6 +2841,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
> err = register_netdevice(tun->dev);
> if (err < 0)
> goto err_detach;
> + tun->flags |= TUN_DEV_REGISTERED;
> }
>
> netif_carrier_on(tun->dev);
This looks just a duplicated of netdev->state? However it lacks
sufficient synchronization like barriers or locks. How about:
- call tun_set_real_num_queues() before register_netdevice() this can
have the same result as what eb0fb363f920 did.
- move tun_attach() after register_netdevice() this makes sure we won't
publish tfile->tun until we are sure at least one refcnt is held by
register_netdevice()?
Thanks
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