Re: NULL pointer dereference in the kernel 3.10

[Xishi Qiu]

On 2017/4/10 14:42, Hillf Danton wrote:

> On April 08, 2017 9:40 PM zhong Jiang wrote: 
>>
>> when runing the stabile docker cases in the vm.   The following issue will come up.
>>
>> #40 [ffff8801b57ffb30] async_page_fault at ffffffff8165c9f8
>>     [exception RIP: down_read_trylock+5]
>>     RIP: ffffffff810aca65  RSP: ffff8801b57ffbe8  RFLAGS: 00010202
>>     RAX: 0000000000000000  RBX: ffff88018ae858c1  RCX: 0000000000000000
>>     RDX: 0000000000000000  RSI: 0000000000000000  RDI: 0000000000000008
>>     RBP: ffff8801b57ffc10   R8: ffffea0006903de0   R9: ffff8800b3c61810
>>     R10: 00000000000022cb  R11: 0000000000000000  R12: ffff88018ae858c0
>>     R13: ffffea0006903dc0  R14: 0000000000000008  R15: ffffea0006903dc0
>>     ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0000
>> #41 [ffff8801b57ffbe8] page_lock_anon_vma_read at ffffffff811b241c
>> #42 [ffff8801b57ffc18] page_referenced at ffffffff811b26a7
>> #43 [ffff8801b57ffc90] shrink_active_list at ffffffff8118d634
>> #44 [ffff8801b57ffd48] balance_pgdat at ffffffff8118f088
>> #45 [ffff8801b57ffe20] kswapd at ffffffff8118f633
>> #46 [ffff8801b57ffec8] kthread at ffffffff810a795f
>> #47 [ffff8801b57fff50] ret_from_fork at ffffffff81665398
>> crash> struct page.mapping ffffea0006903dc0
>>   mapping = 0xffff88018ae858c1
>> crash> struct anon_vma 0xffff88018ae858c0
>> struct anon_vma {
>>   root = 0x0,
>>   rwsem = {
>>     count = 0,
>>     wait_lock = {
>>       raw_lock = {
>>         {
>>           head_tail = 1,
>>           tickets = {
>>             head = 1,
>>             tail = 0
>>           }
>>         }
>>       }
>>     },
>>     wait_list = {
>>       next = 0x0,
>>       prev = 0x0
>>     }
>>   },
>>   refcount = {
>>     counter = 0
>>   },
>>   rb_root = {
>>     rb_node = 0x0
>>   }
>> }
>>
>> This maks me wonder,  the anon_vma do not come from slab structure.
>> and the content is abnormal. IMO,  At least anon_vma->root will not NULL.
>> The issue can be reproduced every other week.
>>
> Check please if commit 
> 624483f3ea8 ("mm: rmap: fix use-after-free in __put_anon_vma")
> is included in the 3.10 you are running.
> 

Hi Hillf,

We missed this patch in RHEL 7.2
Could you please give more details for how it triggered?

Thanks,
Xishi QIu

> btw, why not run the mainline?
> 
> Hillf
> 
> 
> 
> .
>