Re: [PATCH v2] ipvs: Fix use-after-free in ip_vs_in

[Julian Anastasov]

	Hello,

On Fri, 17 May 2019, YueHaibing wrote:

> BUG: KASAN: use-after-free in ip_vs_in.part.29+0xe8/0xd20 [ip_vs]
> Read of size 4 at addr ffff8881e9b26e2c by task sshd/5603
> 
> CPU: 0 PID: 5603 Comm: sshd Not tainted 4.19.39+ #30
> Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> Call Trace:
>  dump_stack+0x71/0xab
>  print_address_description+0x6a/0x270
>  kasan_report+0x179/0x2c0
>  ip_vs_in.part.29+0xe8/0xd20 [ip_vs]
>  ip_vs_in+0xd8/0x170 [ip_vs]
>  nf_hook_slow+0x5f/0xe0
>  __ip_local_out+0x1d5/0x250
>  ip_local_out+0x19/0x60
>  __tcp_transmit_skb+0xba1/0x14f0
>  tcp_write_xmit+0x41f/0x1ed0
>  ? _copy_from_iter_full+0xca/0x340
>  __tcp_push_pending_frames+0x52/0x140
>  tcp_sendmsg_locked+0x787/0x1600
>  ? tcp_sendpage+0x60/0x60
>  ? inet_sk_set_state+0xb0/0xb0
>  tcp_sendmsg+0x27/0x40
>  sock_sendmsg+0x6d/0x80
>  sock_write_iter+0x121/0x1c0
>  ? sock_sendmsg+0x80/0x80
>  __vfs_write+0x23e/0x370
>  vfs_write+0xe7/0x230
>  ksys_write+0xa1/0x120
>  ? __ia32_sys_read+0x50/0x50
>  ? __audit_syscall_exit+0x3ce/0x450
>  do_syscall_64+0x73/0x200
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7ff6f6147c60
> Code: 73 01 c3 48 8b 0d 28 12 2d 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d 5d 73 2d 00 00 75 10 b8 01 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83
> RSP: 002b:00007ffd772ead18 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 0000000000000034 RCX: 00007ff6f6147c60
> RDX: 0000000000000034 RSI: 000055df30a31270 RDI: 0000000000000003
> RBP: 000055df30a31270 R08: 0000000000000000 R09: 0000000000000000
> R10: 00007ffd772ead70 R11: 0000000000000246 R12: 00007ffd772ead74
> R13: 00007ffd772eae20 R14: 00007ffd772eae24 R15: 000055df2f12ddc0
> 
> Allocated by task 6052:
>  kasan_kmalloc+0xa0/0xd0
>  __kmalloc+0x10a/0x220
>  ops_init+0x97/0x190
>  register_pernet_operations+0x1ac/0x360
>  register_pernet_subsys+0x24/0x40
>  0xffffffffc0ea016d
>  do_one_initcall+0x8b/0x253
>  do_init_module+0xe3/0x335
>  load_module+0x2fc0/0x3890
>  __do_sys_finit_module+0x192/0x1c0
>  do_syscall_64+0x73/0x200
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Freed by task 6067:
>  __kasan_slab_free+0x130/0x180
>  kfree+0x90/0x1a0
>  ops_free_list.part.7+0xa6/0xc0
>  unregister_pernet_operations+0x18b/0x1f0
>  unregister_pernet_subsys+0x1d/0x30
>  ip_vs_cleanup+0x1d/0xd2f [ip_vs]
>  __x64_sys_delete_module+0x20c/0x300
>  do_syscall_64+0x73/0x200
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> The buggy address belongs to the object at ffff8881e9b26600 which belongs to the cache kmalloc-4096 of size 4096
> The buggy address is located 2092 bytes inside of 4096-byte region [ffff8881e9b26600, ffff8881e9b27600)
> The buggy address belongs to the page:
> page:ffffea0007a6c800 count:1 mapcount:0 mapping:ffff888107c0e600 index:0x0 compound_mapcount: 0
> flags: 0x17ffffc0008100(slab|head)
> raw: 0017ffffc0008100 dead000000000100 dead000000000200 ffff888107c0e600
> raw: 0000000000000000 0000000080070007 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> 
> while unregistering ipvs module, ops_free_list calls
> __ip_vs_cleanup, then nf_unregister_net_hooks be called to
> do remove nf hook entries. It need a RCU period to finish,
> however net->ipvs is set to NULL immediately, which will
> trigger NULL pointer dereference when a packet is hooked
> and handled by ip_vs_in where net->ipvs is dereferenced.
> 
> Another scene is ops_free_list call ops_free to free the
> net_generic directly while __ip_vs_cleanup finished, then
> calling ip_vs_in will triggers use-after-free.
> 
> This patch moves nf_unregister_net_hooks from __ip_vs_cleanup()
> to __ip_vs_dev_cleanup(),  where rcu_barrier() is called by
> unregister_pernet_device -> unregister_pernet_operations,
> that will do the needed grace period.
> 
> Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> Fixes: efe41606184e ("ipvs: convert to use pernet nf_hook api")
> Suggested-by: Julian Anastasov <ja@xxxxxx>
> Signed-off-by: YueHaibing <yuehaibing@xxxxxxxxxx>

	Looks good to me, thanks!

Acked-by: Julian Anastasov <ja@xxxxxx>

	It should restore the order of unregistrations before
the mentioned commit and to ensure grace period before stopping
the traffic and unregistering ipvs_core_ops where traffic is not
expected.

> ---
> v2: fix by moving nf_unregister_net_hooks from __ip_vs_cleanup() to __ip_vs_dev_cleanup()
> ---
>  net/netfilter/ipvs/ip_vs_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
> index 14457551bcb4..8ebf21149ec3 100644
> --- a/net/netfilter/ipvs/ip_vs_core.c
> +++ b/net/netfilter/ipvs/ip_vs_core.c
> @@ -2312,7 +2312,6 @@ static void __net_exit __ip_vs_cleanup(struct net *net)
>  {
>  	struct netns_ipvs *ipvs = net_ipvs(net);
>  
> -	nf_unregister_net_hooks(net, ip_vs_ops, ARRAY_SIZE(ip_vs_ops));
>  	ip_vs_service_net_cleanup(ipvs);	/* ip_vs_flush() with locks */
>  	ip_vs_conn_net_cleanup(ipvs);
>  	ip_vs_app_net_cleanup(ipvs);
> @@ -2327,6 +2326,7 @@ static void __net_exit __ip_vs_dev_cleanup(struct net *net)
>  {
>  	struct netns_ipvs *ipvs = net_ipvs(net);
>  	EnterFunction(2);
> +	nf_unregister_net_hooks(net, ip_vs_ops, ARRAY_SIZE(ip_vs_ops));
>  	ipvs->enable = 0;	/* Disable packet reception */
>  	smp_wmb();
>  	ip_vs_sync_net_cleanup(ipvs);
> -- 
> 2.20.1

Regards

--
Julian Anastasov <ja@xxxxxx>