Re: NULL pointer dereference in the kernel 3.10

[Hillf Danton]

On April 10, 2017 4:57 PM Xishi Qiu wrote: 
> 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.
> >
> We missed this patch in RHEL 7.2
> Could you please give more details for how it triggered?

Sorry, I could not. 
I guess it is UAF as described in the log of that commit.
And if it works for you, we know how.

Hillf