Linux内核网络调度器的漏洞和利用——专属SLAB提权
背景
The u32 filter Overview
所在模块：
net/sched/cls_u32.cUgly (or Universal) 32bit key Packet Classifier.
Linux TC(traffic control) 流量控制介绍
Linux TC 对多个特定的ip施加不同的吞吐量throughput以及延迟delay限制
netlink与TC
TC是基于Netlink协议实现的。
默认的Qdisc
多队列默认Qdisc
一个定制的qdisc设置
一个例子
传输质量控制，传输的带宽和延时
使用一些SHELL命令就可以实现对TC的使用。也可以通过Netlink编程实现。
漏洞挖掘
为了2021年天府杯比赛，我整理了syzkaller之前本地打出来的漏洞。发现一个UAF在专属SLAB上的漏洞，因为这种漏洞之前没有过利用，但报着试试看的心态给
漏洞给刘永进行分析，发现这个UAF在专属SLAB上的漏洞，可能可以实现提权。大概在10月左右实现漏洞利用。又因为还有其它漏洞可以参加比赛，而这个漏洞的隐蔽性和提权成功率相对比较好，而且一个漏洞可以完成信息泄漏和提权，所以予以保留。
[ 203.112091] ==================================================================
[ 203.112113] BUG: KASAN: use-after-free in sock_prot_inuse_add+0x80/0x90
[ 203.112121] Read of size 8 at addr ffff888106660188 by task poc/6597
[ 203.112134] CPU: 0 PID: 6597 Comm: poc Tainted: G ---------r- - 4.18.0+ #32
[ 203.112138] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/22/2020
[ 203.112140] Call Trace:
[ 203.112148] dump_stack+0xa4/0xea
[ 203.112164] print_address_description.constprop.5+0x1e/0x230
[ 203.112197] __kasan_report.cold.7+0x37/0x82
[ 203.112210] kasan_report+0x3b/0x50
[ 203.112217] sock_prot_inuse_add+0x80/0x90
[ 203.112224] netlink_release+0x97f/0x1190
[ 203.112257] __sock_release+0xd3/0x2b0
[ 203.112262] sock_close+0x1e/0x30
[ 203.112267] __fput+0x2d4/0x840
[ 203.112275] task_work_run+0x16e/0x1d0
[ 203.112284] exit_to_usermode_loop+0x207/0x230
[ 203.112290] do_syscall_64+0x3f5/0x470
[ 203.112302] entry_SYSCALL_64_after_hwframe+0x65/0xca
[ 203.112308] RIP: 0033:0x7fee34abd1a8
[ 203.112315] Code: 07 02 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 f3 0f 1e fa 48 8d 05 b5 44 2d 00 8b 00 85 c0 75 17 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 40 c3 0f 1f 80 00 00 00 00 53 89 fb 48 83 ec
[ 203.112318] RSP: 002b:00007ffdb62366c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
[ 203.112323] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007fee34abd1a8
[ 203.112327] RDX: 0000000000000000 RSI: 00000000200001c0 RDI: 0000000000000004
[ 203.112330] RBP: 00007ffdb62366e0 R08: 00007ffdb62366e0 R09: 00007ffdb62366e0
[ 203.112333] R10: 00007ffdb62366e0 R11: 0000000000000246 R12: 0000000000400f50
[ 203.112337] R13: 00007ffdb6236820 R14: 0000000000000000 R15: 0000000000000000
[ 203.112345] Allocated by task 6247:
[ 203.112353] kasan_save_stack+0x1d/0x80
[ 203.112359] __kasan_kmalloc.constprop.10+0xc1/0xd0
[ 203.112367] slab_post_alloc_hook+0x43/0x280
[ 203.112377] kmem_cache_alloc+0x131/0x280
[ 203.112386] copy_net_ns+0xec/0x330
[ 203.112395] create_new_namespaces+0x583/0x9a0
[ 203.112404] unshare_nsproxy_namespaces+0xcb/0x200
[ 203.112414] ksys_unshare+0x468/0x8d0
[ 203.112423] __x64_sys_unshare+0x36/0x50
[ 203.112432] do_syscall_64+0xe4/0x470
[ 203.112443] entry_SYSCALL_64_after_hwframe+0x65/0xca
[ 203.112453] Freed by task 59:
[ 203.112487] kasan_save_stack+0x1d/0x80
[ 203.112510] kasan_set_track+0x20/0x30
[ 203.112535] kasan_set_free_info+0x1f/0x30
[ 203.112557] __kasan_slab_free+0x108/0x150
[ 203.112578] kmem_cache_free+0x83/0x430
[ 203.112593] net_drop_ns+0x7d/0x90
[ 203.112604] cleanup_net+0x6ee/0x960
[ 203.112619] process_one_work+0x742/0x1030
[ 203.112632] worker_thread+0x95/0xce0
[ 203.112643] kthread+0x32c/0x3f0
[ 203.112654] ret_from_fork+0x35/0x40
[ 203.112686] The buggy address belongs to the object at ffff888106660000
which belongs to the cache net_namespace of size 8000
[ 203.112698] The buggy address is located 392 bytes inside of
8000-byte region [ffff888106660000, ffff888106661f40)
[ 203.112704] The buggy address belongs to the page:
[ 203.112739] page:ffffea0004199800 refcount:1 mapcount:0 mapping:00000000306a7880 index:0xffff888106664080 head:ffffea0004199800 order:3 compound_mapcount:0 compound_pincount:0
[ 203.112752] flags: 0x17ffffc0008100(slab|head)
[ 203.112774] raw: 0017ffffc0008100 dead000000000100 dead000000000200 ffff88810b6ff600
[ 203.112792] raw: ffff888106664080 0000000080030002 00000001ffffffff ffff888101f819c1
[ 203.112798] page dumped because: kasan: bad access detected
[ 203.112803] pages's memcg:ffff888101f819c1
[ 203.112814] Memory state around the buggy address:
[ 203.112831] ffff888106660080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 203.112857] ffff888106660100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 203.112868] >ffff888106660180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 203.112873] ^
[ 203.112884] ffff888106660200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 203.112894] ffff888106660280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 203.112900] =================================================================
但是在2022/04/12在syzbot上与打出了类似的漏洞，是一个Warning，随后被社区修复。最后这个漏洞利用输出到国内的安全大赛。
漏洞原理
原始PoC
syzkaller自动转化的PoC可以稳定地触发漏洞。
分配
unshare
|-> __x64_sys_unshare
|-> ksys_unshare
|-> unshare_nsproxy_namespaces
|-> copy_net_ns
|-> kmem_cache_alloc
释放
exit_process
|-> ret_from_fork
|-> kthread
|-> worker_thread
|-> process_one_work
|-> cleanup_net
|-> net_drop_ns
|-> kmem_cache_free
UAF
sock_close
|-> exit_to_usermode_loop
|-> task_work_run
|-> __fput
|-> sock_close
|-> __sock_release
|-> sock_prot_inuse_add
分配net的源代码
net/core/net_namespace.c
445 struct net *copy_net_ns(unsigned long flags,
446 struct user_namespace *user_ns, struct net *old_net)
447 {
448 struct ucounts *ucounts;
449 struct net *net;
450 int rv;
451
452 if (!(flags & CLONE_NEWNET))
453 return get_net(old_net);
454
455 ucounts = inc_net_namespaces(user_ns);
456 if (!ucounts)
457 return ERR_PTR(-ENOSPC);
458
459 net = net_alloc(); <---
460 if (!net) {
461 rv = -ENOMEM;
462 goto dec_ucounts;
463 }
464 refcount_set(&net->passive, 1);
465 net->ucounts = ucounts;
466 get_user_ns(user_ns);
....
487 return net;
488 }
395 static struct net *net_alloc(void)
396 {
397 struct net *net = NULL;
398 struct net_generic *ng;
399
400 ng = net_alloc_generic();
401 if (!ng)
402 goto out;
403
404 net = kmem_cache_zalloc(net_cachep, GFP_KERNEL); <---
405 if (!net)
406 goto out_free;
407
....
427 }
$ sudo cat /sys/kernel/slab/net_namespace/object_size
4928
$ sudo cat /sys/kernel/slab/net_namespace/order
3释放函数
437 void net_drop_ns(void *p)
438 {
439 struct net *net = (struct net *)p;
440
441 if (net)
442 net_free(net);
443 }
444UAF的结构（下文将net_namespace统称为net结构）
56 struct net {
57 /* First cache line can be often dirtied.
58 ¦* Do not place here read-mostly fields.
59 ¦*/
60 refcount_t passive; /* To decide when the network
61 ¦* namespace should be freed.
62 ¦*/
63 spinlock_t rules_mod_lock;
64
65 unsigned int dev_unreg_count;
66
67 unsigned int dev_base_seq; /* protected by rtnl_mutex */
68 int ifindex;
69
70 spinlock_t nsid_lock;
71 atomic_t fnhe_genid;
72
73 struct list_head list; /* list of network namespaces */
74 struct list_head exit_list; /* To linked to call pernet exit
75 ¦* methods on dead net (
76 ¦* pernet_ops_rwsem read locked),
77 ¦* or to unregister pernet ops
78 ¦* (pernet_ops_rwsem write locked).
79 ¦*/
80 struct llist_node cleanup_list; /* namespaces on death row */
81
82 #ifdef CONFIG_KEYS
83 struct key_tag *key_domain; /* Key domain of operation tag */
84 #endif
85 struct user_namespace *user_ns; /* Owning user namespace */
86 struct ucounts *ucounts;
87 struct idr netns_ids;
88
89 struct ns_common ns; <---/*现实任意地址读*/
90
91 struct list_head dev_base_head;
92 struct proc_dir_entry *proc_net;
93 struct proc_dir_entry *proc_net_stat;
94
95 #ifdef CONFIG_SYSCTL
96 struct ctl_table_set sysctls;
97 #endif
98
99 struct sock *rtnl; /* rtnetlink socket */
100 struct sock *genl_sock;
101
102 struct uevent_sock *uevent_sock; /* uevent socket */
103
104 struct hlist_head *dev_name_head;
105 struct hlist_head *dev_index_head;
106 struct raw_notifier_head netdev_chain;
107
108 /* Note that @hash_mix can be read millions times per second,
109 ¦* it is critical that it is on a read_mostly cache line.
110 ¦*/
111 u32 hash_mix;
112
113 struct net_device *loopback_dev; /* The loopback */
114
115 /* core fib_rules */
116 struct list_head rules_ops;
117
118 struct netns_core core;
119 struct netns_mib mib;
120 struct netns_packet packet;
121 struct netns_unix unx;
122 struct netns_nexthop nexthop;
123 struct netns_ipv4 ipv4;
124 #if IS_ENABLED(CONFIG_IPV6)
125 struct netns_ipv6 ipv6;
126 #endif
127 #if IS_ENABLED(CONFIG_IEEE802154_6LOWPAN)
128 struct netns_ieee802154_lowpan ieee802154_lowpan;
129 #endif
130 #if defined(CONFIG_IP_SCTP) || defined(CONFIG_IP_SCTP_MODULE)
131 struct netns_sctp sctp;
132 #endif
133 #ifdef CONFIG_NETFILTER
134 struct netns_nf nf;
135 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
136 struct netns_ct ct;
137 #endif
138 #if defined(CONFIG_NF_TABLES) || defined(CONFIG_NF_TABLES_MODULE)
139 struct netns_nftables nft;
140 #endif
141 #endif
142 #ifdef CONFIG_WEXT_CORE
143 struct sk_buff_head wext_nlevents;
144 #endif
145 struct net_generic __rcu *gen;
146
147 /* Used to store attached BPF programs */
148 struct netns_bpf bpf;
149
150 /* Note : following structs are cache line aligned */
151 #ifdef CONFIG_XFRM
152 struct netns_xfrm xfrm;
153 #endif
154
155 u64 net_cookie; /* written once */
156
157 #if IS_ENABLED(CONFIG_IP_VS)
158 struct netns_ipvs *ipvs;
159 #endif
160 #if IS_ENABLED(CONFIG_MPLS)
161 struct netns_mpls mpls;
162 #endif
163 #if IS_ENABLED(CONFIG_CAN)
164 struct netns_can can;
165 #endif
166 #ifdef CONFIG_XDP_SOCKETS
167 struct netns_xdp xdp;
168 #endif
169 #if IS_ENABLED(CONFIG_MCTP)
170 struct netns_mctp mctp;
171 #endif
172 #if IS_ENABLED(CONFIG_CRYPTO_USER)
173 struct sock *crypto_nlsk;
174 #endif
175 struct sock *diag_nlsk;
176 #if IS_ENABLED(CONFIG_SMC)
177 struct netns_smc smc;
178 #endif
179 } __randomize_layout;
PoC改写
经过进一步的分析，是因为u32_change函数会错误地减少nets的引用计数，从而导致UAF的逻辑问题。从此出发，优化了PoC的触发路径。
u32_change()
|--> u32_destroy_key()
|--> tcf_exts_put_net()
|--> put_net()同时构造出对net上引用计数减1的逻辑原语。
优化后的触发流程如下：
[ 253.623920] ------------[ cut here ]------------
[ 253.623929] refcount_t: underflow; use-after-free.
[ 253.623984] WARNING: CPU: 0 PID: 4009 at lib/refcount.c:28 refcount_warn_saturate+0x10c/0x1f0
[ 253.624026] Modules linked in: act_police cls_u32 ip6_gre gre ip6_tunnel tunnel6 uas usb_storage binfmt_misc snd_seq_dummy snd_hrtimer vsock_loopback vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vsock snd_ens1371 snd_ac97_codec gameport ac97_bus snd_pcm snd_seq_midi snd_seq_midi_event snd_rawmidi intel_rapl_msr intel_rapl_common nls_iso8859_1 snd_seq crct10dif_pclmul ghash_clmulni_intel sch_fq_codel aesni_intel snd_seq_device crypto_simd snd_timer cryptd snd vmw_balloon joydev rapl input_leds soundcore vmw_vmci serio_raw vmwgfx ttm drm_kms_helper mac_hid cec rc_core fb_sys_fops syscopyarea sysfillrect sysimgblt ipmi_devintf ipmi_msghandler msr parport_pc ppdev lp drm parport ip_tables x_tables autofs4 hid_generic crc32_pclmul psmouse usbhid ahci mptspi hid libahci mptscsih e1000 mptbase scsi_transport_spi i2c_piix4 pata_acpi floppy
[ 253.624306] CPU: 0 PID: 4009 Comm: apparmor_parser Tainted: G B 5.15.30+ #2
[ 253.624330] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/22/2020
[ 253.624338] RIP: 0010:refcount_warn_saturate+0x10c/0x1f0
[ 253.624351] Code: 1d 6d 3a 1d 03 31 ff 89 de e8 90 f1 18 ff 84 db 75 a0 e8 47 f6 18 ff 48 c7 c7 e0 f0 65 85 c6 05 4d 3a 1d 03 01 e8 f2 76 57 01 <0f> 0b eb 84 e8 2b f6 18 ff 0f b6 1d 36 3a 1d 03 31 ff 89 de e8 5b
[ 253.624361] RSP: 0000:ffff888137fafc90 EFLAGS: 00010282
[ 253.624369] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[ 253.624376] RDX: ffff88810caf0000 RSI: 0000000000000100 RDI: ffffed1026ff5f84
[ 253.624383] RBP: ffff888137fafca0 R08: 0000000000000100 R09: ffff8881e183098b
[ 253.624390] R10: 0000000000000000 R11: 0000000000000001 R12: ffff888120ec008c
[ 253.624397] R13: ffff888105f42000 R14: ffff888120ec0000 R15: ffff888120ec008c
[ 253.624404] FS: 00007fc64fc8d740(0000) GS:ffff8881e1800000(0000) knlGS:0000000000000000
[ 253.624414] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 253.624421] CR2: 000055893f3fadf9 CR3: 0000000135002001 CR4: 00000000003706f0
[ 253.624445] Call Trace:
[ 253.624451] <TASK>
[ 253.624458] __sk_destruct+0x693/0x790
[ 253.624478] sk_destruct+0xd3/0x100
[ 253.624494] __sk_free+0xfe/0x400
[ 253.624509] sk_free+0x88/0xc0
[ 253.624524] deferred_put_nlk_sk+0x170/0x320
[ 253.624544] rcu_core+0x51a/0x1250
[ 253.624607] rcu_core_si+0xe/0x10
[ 253.624618] __do_softirq+0x189/0x536
[ 253.624631] irq_exit_rcu+0xec/0x130
[ 253.624641] sysvec_apic_timer_interrupt+0x40/0x90
[ 253.624664] asm_sysvec_apic_timer_interrupt+0x12/0x20
[ 253.624675] RIP: 0033:0x55893f2e92d2
[ 253.624685] Code: c3 0f 1f 80 00 00 00 00 48 39 cb 74 3b 48 8b 7d 10 49 89 d8 4c 89 ee 48 8b 07 48 89 54 24 68 44 89 f2 48 89 4c 24 60 4c 89 e1 <48> 8b 40 38 48 83 c4 28 5b 5d 41 5c 41 5d 41 5e 41 5f ff e0 66 2e
[ 253.624694] RSP: 002b:00007ffc26b6c960 EFLAGS: 00000202
[ 253.624703] RAX: 000055893f3ec3a0 RBX: 0000558940c048d0 RCX: 000055893f3eb588
[ 253.624710] RDX: 0000000000000006 RSI: 0000000000000000 RDI: 000055893f3eb510
[ 253.624717] RBP: 000055893f3eb528 R08: 0000558940c048d0 R09: 000055893f3eb4a0
[ 253.624723] R10: 0000558940e14270 R11: 00007fc64fea9ce0 R12: 000055893f3eb588
[ 253.624730] R13: 0000000000000000 R14: 0000000000000006 R15: 000055893f3a48e8
[ 253.624740] </TASK>
[ 253.624743] ---[ end trace ddbeecae4d8b2b8c ]---
[ 253.626421] ------------[ cut here ]------------
[ 253.626431] refcount_t: saturated; leaking memory.
[ 253.626489] WARNING: CPU: 3 PID: 309 at lib/refcount.c:19 refcount_warn_saturate+0x1bd/0x1f0
[ 253.626513] Modules linked in: act_police cls_u32 ip6_gre gre ip6_tunnel tunnel6 uas usb_storage binfmt_misc snd_seq_dummy snd_hrtimer vsock_loopback vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vsock snd_ens1371 snd_ac97_codec gameport ac97_bus snd_pcm snd_seq_midi snd_seq_midi_event snd_rawmidi intel_rapl_msr intel_rapl_common nls_iso8859_1 snd_seq crct10dif_pclmul ghash_clmulni_intel sch_fq_codel aesni_intel snd_seq_device crypto_simd snd_timer cryptd snd vmw_balloon joydev rapl input_leds soundcore vmw_vmci serio_raw vmwgfx ttm drm_kms_helper mac_hid cec rc_core fb_sys_fops syscopyarea sysfillrect sysimgblt ipmi_devintf ipmi_msghandler msr parport_pc ppdev lp drm parport ip_tables x_tables autofs4 hid_generic crc32_pclmul psmouse usbhid ahci mptspi hid libahci mptscsih e1000 mptbase scsi_transport_spi i2c_piix4 pata_acpi floppy
[ 253.626837] CPU: 3 PID: 309 Comm: kworker/u256:28 Tainted: G B W 5.15.30+ #2
[ 253.626851] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/22/2020
[ 253.626859] Workqueue: netns cleanup_net
[ 253.626874] RIP: 0010:refcount_warn_saturate+0x1bd/0x1f0
[ 253.626888] Code: 03 31 ff 89 de e8 e3 f0 18 ff 84 db 0f 85 ef fe ff ff e8 96 f5 18 ff 48 c7 c7 e0 ef 65 85 c6 05 9f 39 1d 03 01 e8 41 76 57 01 <0f> 0b e9 d0 fe ff ff e8 77 f5 18 ff 48 c7 c7 40 f1 65 85 c6 05 7c
[ 253.626899] RSP: 0000:ffff8881032ff688 EFLAGS: 00010282
[ 253.626908] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
[ 253.626915] RDX: ffff888103093380 RSI: 0000000000000000 RDI: ffffed102065fec3
[ 253.626922] RBP: ffff8881032ff698 R08: 0000000000000000 R09: ffff8881e19b098b
[ 253.626930] R10: 0000000000000000 R11: 0000000000000001 R12: ffff888120ec008c
[ 253.626936] R13: ffff88812dc76500 R14: dffffc0000000000 R15: 00000000c0000000
[ 253.626944] FS: 0000000000000000(0000) GS:ffff8881e1980000(0000) knlGS:0000000000000000
[ 253.626954] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 253.626961] CR2: 00007f2ede8e1024 CR3: 00000001736a6006 CR4: 00000000003706e0
[ 253.626993] Call Trace:
[ 253.626997] <TASK>
[ 253.627006] u32_clear_hnode+0x4c7/0x680 [cls_u32]
[ 253.627058] u32_destroy_hnode.isra.0+0xa4/0x240 [cls_u32]
[ 253.627069] u32_destroy+0x2da/0x390 [cls_u32]
[ 253.627080] tcf_proto_destroy+0x85/0x300
[ 253.627091] tcf_proto_put+0x9c/0xd0
[ 253.627101] tcf_chain_flush+0x1c0/0x310
[ 253.627112] __tcf_block_put+0x158/0x2e0
[ 253.627123] tcf_block_put+0xe3/0x130
[ 253.627178] fq_codel_destroy+0x3c/0xb0 [sch_fq_codel]
[ 253.627189] qdisc_destroy+0xb1/0x2a0
[ 253.627200] qdisc_put+0xe0/0x100
[ 253.627211] dev_shutdown+0x253/0x390
[ 253.627224] unregister_netdevice_many+0x7e0/0x1720
[ 253.627282] ip6gre_exit_batch_net+0x36b/0x450 [ip6_gre]
[ 253.627367] ops_exit_list+0x115/0x160
[ 253.627378] cleanup_net+0x475/0xb40
[ 253.627403] process_one_work+0x8bf/0x11d0
[ 253.627416] worker_thread+0x60b/0x1340
[ 253.627441] kthread+0x388/0x470
[ 253.627461] ret_from_fork+0x22/0x30
[ 253.627476] </TASK>
[ 253.627480] ---[ end trace ddbeecae4d8b2b8d ]---
漏洞补丁
在u32_change函数中，不应该执行tcf_exts_put_net函数（使得nets上的引用计数减少1）。
author Eric Dumazet <edumazet@google.com> 2022-04-13 10:35:41 -0700
committer Jakub Kicinski <kuba@kernel.org> 2022-04-15 14:26:11 -0700
commit 3db09e762dc79584a69c10d74a6b98f89a9979f8 (patch)
tree 1a269d290124f61d42c2cb059de92a0661f818a5
parent f3226eed54318e7bdc186f8f7ed27bcd3cb8b681 (diff)
download linux-3db09e762dc79584a69c10d74a6b98f89a9979f8.tar.gz
net/sched: cls_u32: fix netns refcount changes in u32_change()
We are now able to detect extra put_net() at the moment
they happen, instead of much later in correct code paths.
u32_init_knode() / tcf_exts_init() populates the ->exts.net
pointer, but as mentioned in tcf_exts_init(),
the refcount on netns has not been elevated yet.
The refcount is taken only once tcf_exts_get_net()
is called.
So the two u32_destroy_key() calls from u32_change()
are attempting to release an invalid reference on the netns.
syzbot report:
refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 0 PID: 21708 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
Modules linked in:
CPU: 0 PID: 21708 Comm: syz-executor.5 Not tainted 5.18.0-rc2-next-20220412-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
Code: 1d 14 b6 b2 09 31 ff 89 de e8 6d e9 89 fd 84 db 75 e0 e8 84 e5 89 fd 48 c7 c7 40 aa 26 8a c6 05 f4 b5 b2 09 01 e8 e5 81 2e 05 <0f> 0b eb c4 e8 68 e5 89 fd 0f b6 1d e3 b5 b2 09 31 ff 89 de e8 38
RSP: 0018:ffffc900051af1b0 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff8160a0c8 RDI: fffff52000a35e28
RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff81604a9e R11: 0000000000000000 R12: 1ffff92000a35e3b
R13: 00000000ffffffef R14: ffff8880211a0194 R15: ffff8880577d0a00
FS: 00007f25d183e700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f19c859c028 CR3: 0000000051009000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__refcount_dec include/linux/refcount.h:344 [inline]
refcount_dec include/linux/refcount.h:359 [inline]
ref_tracker_free+0x535/0x6b0 lib/ref_tracker.c:118
netns_tracker_free include/net/net_namespace.h:327 [inline]
put_net_track include/net/net_namespace.h:341 [inline]
tcf_exts_put_net include/net/pkt_cls.h:255 [inline]
u32_destroy_key.isra.0+0xa7/0x2b0 net/sched/cls_u32.c:394
u32_change+0xe01/0x3140 net/sched/cls_u32.c:909
tc_new_tfilter+0x98d/0x2200 net/sched/cls_api.c:2148
rtnetlink_rcv_msg+0x80d/0xb80 net/core/rtnetlink.c:6016
netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2495
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x904/0xe00 net/netlink/af_netlink.c:1921
sock_sendmsg_nosec net/socket.c:705 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:725
____sys_sendmsg+0x6e2/0x800 net/socket.c:2413
___sys_sendmsg+0xf3/0x170 net/socket.c:2467
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2496
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f25d0689049
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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
RSP: 002b:00007f25d183e168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f25d079c030 RCX: 00007f25d0689049
RDX: 0000000000000000 RSI: 0000000020000340 RDI: 0000000000000005
RBP: 00007f25d06e308d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd0b752e3f R14: 00007f25d183e300 R15: 0000000000022000
</TASK>
Fixes: 35c55fc156d8 ("cls_u32: use tcf_exts_get_net() before call_rcu()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat
-rw-r--r-- net/sched/cls_u32.c 16
1 files changed, 10 insertions, 6 deletions
diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index cf5649292ee00..fcba6c43ba509 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -386,14 +386,19 @@ static int u32_init(struct tcf_proto *tp)
return 0;
}
-static int u32_destroy_key(struct tc_u_knode *n, bool free_pf)
+static void __u32_destroy_key(struct tc_u_knode *n)
{
struct tc_u_hnode *ht = rtnl_dereference(n->ht_down);
tcf_exts_destroy(&n->exts);
- tcf_exts_put_net(&n->exts);
if (ht && --ht->refcnt == 0)
kfree(ht);
+ kfree(n);
+}
+
+static void u32_destroy_key(struct tc_u_knode *n, bool free_pf)
+{
+ tcf_exts_put_net(&n->exts);
#ifdef CONFIG_CLS_U32_PERF
if (free_pf)
free_percpu(n->pf);
@@ -402,8 +407,7 @@ static int u32_destroy_key(struct tc_u_knode *n, bool free_pf)
if (free_pf)
free_percpu(n->pcpu_success);
#endif
- kfree(n);
- return 0;
+ __u32_destroy_key(n);
}
/* u32_delete_key_rcu should be called when free'ing a copied
@@ -900,13 +904,13 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
extack);
if (err) {
- u32_destroy_key(new, false);
+ __u32_destroy_key(new);
return err;
}
err = u32_replace_hw_knode(tp, new, flags, extack);
if (err) {
- u32_destroy_key(new, false);
+ __u32_destroy_key(new);
return err;
}
问题引入
commit 35c55fc156d85a396a975fc17636f560fc02fd65
Author: Cong Wang <xiyou.wangcong@gmail.com>
Date: Mon Nov 6 13:47:30 2017 -0800
cls_u32: use tcf_exts_get_net() before call_rcu()
Hold netns refcnt before call_rcu() and release it after
the tcf_exts_destroy() is done.
Note, on ->destroy() path we have to respect the return value
of tcf_exts_get_net(), on other paths it should always return
true, so we don't need to care.
Cc: Lucas Bates <lucasb@mojatatu.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index dadd1b344497..b58eccb21f03 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -399,6 +399,7 @@ static int u32_destroy_key(struct tcf_proto *tp, struct tc_u_knode *n,
bool free_pf)
{
tcf_exts_destroy(&n->exts);
+ tcf_exts_put_net(&n->exts);
if (n->ht_down)
n->ht_down->refcnt--;
#ifdef CONFIG_CLS_U32_PERF
@@ -476,6 +477,7 @@ static int u32_delete_key(struct tcf_proto *tp, struct tc_u_knode *key)
RCU_INIT_POINTER(*kp, key->next);
tcf_unbind_filter(tp, &key->res);
+ tcf_exts_get_net(&key->exts);
call_rcu(&key->rcu, u32_delete_key_freepf_rcu);
return 0;
}
所以，漏洞影响的时间范围2017年11月6日~2022年4月13日，持续4年半。
时间轴
| 时间 | |
|---|---|
| 2021年7月27日 | 确认漏洞 |
| 2021年10月 | 完成漏洞利用 |
| 2022年4月12日 | syzbot打出类似漏洞 |
| 2022年4月13日 | 社区修补 |
| 2022年8月 | 参加国内比赛 |
漏洞利用
漏洞利用的步骤分为：
1.通过信息泄漏，过地址随机化；
2.通过run_cmd提升权限。
信息泄漏
第一步：堆布局
1: 填充SLAB中空闲的net
将cache中的net专属SLAB的页全部吃掉，为了让新分配的net使用系统新分配出来的页。图中黄色区域代表堆喷的net objects，如图中的SLAB 1和SLAB 2。
2: 再从新分配的slab中创建victim net
图中红色区域所示。
3:再把victim所在的slab全部吃掉；
如图中的slab A和slab B，其中都用net对象将该8个页大小的slab填满；
第二步：mount net name space
为了后面通过该文件访问victim的引用。
mount("/proc/self/ns/net", "./mynetns", "nsfs", MS_BIND, NULL)第三步：把victim所在的页还到伙伴系统
通过u32_destroy_key将Victim的引用计数减少1
第四步：用户态mmap堆喷victim所在的物理页
将刚刚第三步还回系统的物理页，通过mmap分配得到。
第五步：构造任意地址读
在之前通过mount得到的文件上，调用ioctl(NS_GET_NSTYPE)，用户态就可以得到ns->ops->type的值，因为ops的值可控，所以就能实现任意地址读。
第六步：读取cpu_area_entry，绕过Kaslr
因为系统中cpu_area_entry的虚拟地址(0xfffffe0000000000)是固定的， 而该地址里含有一个被Kaslr后的内核代码段地址。所以可以计算出偏移，进而绕过Kaslr。
fs/nsfs.c
88 static long ns_ioctl(struct file *filp, unsigned int ioctl,
189 unsigned long arg)
190 {
191 struct user_namespace *user_ns;
192 struct ns_common *ns = get_proc_ns(file_inode(filp));
193 uid_t __user *argp;
194 uid_t uid;
195
196 switch (ioctl) {
197 case NS_GET_USERNS:
198 return open_related_ns(ns, ns_get_owner);
199 case NS_GET_PARENT:
200 if (!ns->ops->get_parent)
201 return -EINVAL;
202 return open_related_ns(ns, ns->ops->get_parent);
203 case NS_GET_NSTYPE:
204 return ns->ops->type; <---/*现实任意地址读*/
205 case NS_GET_OWNER_UID:
206 if (ns->ops->type != CLONE_NEWUSER)
207 return -EINVAL;
208 user_ns = container_of(ns, struct user_namespace, ns);
209 argp = (uid_t __user *) arg;
210 uid = from_kuid_munged(current_user_ns(), user_ns->owner);
211 return put_user(uid, argp);
212 default:
213 return -ENOTTY;
214 }
215 }
include/linux/ns_common.h
9 struct ns_common {
10 atomic_long_t stashed;
11 const struct proc_ns_operations *ops; <---
12 unsigned int inum;
13 refcount_t count;
14 };
通过run_cmd提权
在绕过地址随机化后，就可以进行下一步的提权。
第一步：读取victim net的地址
通过task_list读取中当前的task_struct结构，再读取task_struct上的nsproxy的地址，再读取nsproxy上的net指针来实现。
第二步：在用户态构造fake ops
将ops指针指向fake ops
第三步：劫持PC
147 int open_related_ns(struct ns_common *ns,
148 ¦ struct ns_common *(*get_ns)(struct ns_common *ns))
149 {
150 struct path path = {};
151 struct file *f;
152 int err;
153 int fd;
154
155 fd = get_unused_fd_flags(O_CLOEXEC);
156 if (fd < 0)
157 return fd;
158
159 do {
160 struct ns_common *relative;
161
162 relative = get_ns(ns);
163 if (IS_ERR(relative)) {
164 put_unused_fd(fd);
165 return PTR_ERR(relative);
166 }
167
168 err = __ns_get_path(&path, relative);
169 } while (err == -EAGAIN);
170
171 if (err) {
172 put_unused_fd(fd);
173 return err;
174 }
175
176 f = dentry_open(&path, O_RDONLY, current_cred());
177 path_put(&path);
178 if (IS_ERR(f)) {
179 put_unused_fd(fd);
180 fd = PTR_ERR(f);
181 } else
182 fd_install(fd, f);
183
184 return fd;
185 }
owner就是最后劫持的PC，而且ns的数据也可以控制，所以就可以执行run_cmd完成提权。
1371 struct ns_common *ns_get_owner(struct ns_common *ns)
1372 {
1373 struct user_namespace *my_user_ns = current_user_ns();
1374 struct user_namespace *owner, *p;
1375
1376 /* See if the owner is in the current user namespace */
1377 owner = p = ns->ops->owner(ns); <---/*劫持PC*/
1378 for (;;) {
1379 if (!p)
1380 return ERR_PTR(-EPERM);
1381 if (p == my_user_ns)
1382 break;
1383 p = p->parent;
1384 }
1385
1386 return &get_user_ns(owner)->ns;
1387 }
16 struct proc_ns_operations {
17 const char *name;
18 const char *real_ns_name;
19 int type;
20 struct ns_common *(*get)(struct task_struct *task);
21 void (*put)(struct ns_common *ns);
22 int (*install)(struct nsset *nsset, struct ns_common *ns);
23 struct user_namespace *(*owner)(struct ns_common *ns); <---
24 struct ns_common *(*get_parent)(struct ns_common *ns);
25 } __randomize_layout;
参考链接
[1] https://github.com/xdp-project/bpf-examples/tree/master/tc-basic-classifier
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3db09e762dc79584a69c10d74a6b98f89a9979f8
[3] https://syzkaller.appspot.com/bug?id=0ca897284a4e1bbc149ad96f15917e8b31a85d70