Re: mm: NULL ptr deref in balance_dirty_pages_ratelimited

[Bob Liu]

On Wed, Feb 26, 2014 at 3:32 AM, Sasha Levin <sasha.levin@xxxxxxxxxx> wrote:
> Hi all,
>
> While fuzzing with trinity inside a KVM tools running latest -next kernel
> I've stumbled on the following spew:
>
> [  232.869443] BUG: unable to handle kernel NULL pointer dereference at
> 0000000000000020
> [  232.870230] IP: [<mm/page-writeback.c:1612>]
> balance_dirty_pages_ratelimited+0x1e/0x150
> [  232.870230] PGD 586e1d067 PUD 586e1e067 PMD 0
> [  232.870230] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
> [  232.870230] Dumping ftrace buffer:
> [  232.870230]    (ftrace buffer empty)
> [  232.870230] Modules linked in:
> [  232.870230] CPU: 36 PID: 9707 Comm: trinity-c36 Tainted: G        W
> 3.14.0-rc4-next-20140225-sasha-00010-ga117461 #42
> [  232.870230] task: ffff880586dfb000 ti: ffff880586e34000 task.ti:
> ffff880586e34000
> [  232.870230] RIP: 0010:[<mm/page-writeback.c:1612>]
> [<mm/page-writeback.c:1612>] balance_dirty_pages_ratelimited+0x1e/0x150
> [  232.870230] RSP: 0000:ffff880586e35c58  EFLAGS: 00010282
> [  232.870230] RAX: 0000000000000000 RBX: ffff880582831361 RCX:
> 0000000000000007
> [  232.870230] RDX: 0000000000000007 RSI: ffff880586dfbcc0 RDI:
> ffff880582831361
> [  232.870230] RBP: ffff880586e35c78 R08: 0000000000000000 R09:
> 0000000000000000
> [  232.870230] R10: 0000000000000001 R11: 0000000000000001 R12:
> 00007f58007ee000
> [  232.870230] R13: ffff880c8d6d4f70 R14: 0000000000000200 R15:
> ffff880c8dcce710
> [  232.870230] FS:  00007f58018bb700(0000) GS:ffff880c8e800000(0000)
> knlGS:0000000000000000
> [  232.870230] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [  232.870230] CR2: 0000000000000020 CR3: 0000000586e1c000 CR4:
> 00000000000006e0
> [  232.870230] Stack:
> [  232.870230]  ffff880586e35c78 ffff880586e33400 00007f58007ee000
> ffff880c8d6d4f70
> [  232.870230]  ffff880586e35cd8 ffffffff8127d241 0000000000000001
> 0000000000000001
> [  232.870230]  0000000000000000 ffffea0032337080 0000000080000000
> ffff880586e33400
> [  232.870230] Call Trace:
> [  232.870230]  [<mm/memory.c:3467>] do_shared_fault+0x1a1/0x1f0
> [  232.870230]  [<mm/memory.c:3487>] handle_pte_fault+0xc8/0x230
> [  232.870230]  [<arch/x86/include/asm/preempt.h:98>] ? delay_tsc+0xea/0x110
> [  232.870230]  [<mm/memory.c:3770>] __handle_mm_fault+0x36e/0x3a0
> [  232.870230]  [<include/linux/rcupdate.h:829>] ? rcu_read_unlock+0x5d/0x60
> [  232.870230]  [<include/linux/memcontrol.h:148>]
> handle_mm_fault+0x10b/0x1b0
> [  232.870230]  [<arch/x86/mm/fault.c:1147>] ? __do_page_fault+0x2e2/0x590
> [  232.870230]  [<arch/x86/mm/fault.c:1214>] __do_page_fault+0x551/0x590
> [  232.870230]  [<kernel/sched/cputime.c:681>] ?
> vtime_account_user+0x91/0xa0
> [  232.870230]  [<arch/x86/include/asm/atomic.h:26>] ?
> context_tracking_user_exit+0xa8/0x1c0
> [  232.870230]  [<arch/x86/include/asm/preempt.h:98>] ?
> _raw_spin_unlock+0x30/0x50
> [  232.870230]  [<kernel/sched/cputime.c:681>] ?
> vtime_account_user+0x91/0xa0
> [  232.870230]  [<arch/x86/include/asm/atomic.h:26>] ?
> context_tracking_user_exit+0xa8/0x1c0
> [  232.870230]  [<arch/x86/include/asm/atomic.h:26>] do_page_fault+0x3d/0x70
> [  232.870230]  [<arch/x86/kernel/kvm.c:263>] do_async_page_fault+0x35/0x100
> [  232.870230]  [<arch/x86/kernel/entry_64.S:1496>]
> async_page_fault+0x28/0x30
> [  232.870230] Code: 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 48
> 83 ec 20 48 89 5d e8 4c 89 65 f0 4c 89 6d f8 48 89 fb 48 8b 87 50 01 00 00
> <f6> 40 20 01 0f 85 18 01 00 00 65 48 8b 14 25 40 da 00 00 44 8b
> [  232.870230] RIP  [<mm/page-writeback.c:1612>]
> balance_dirty_pages_ratelimited+0x1e/0x150
> [  232.870230]  RSP <ffff880586e35c58>
> [  232.870230] CR2: 0000000000000020
>
>

Could you please test below patch? I think it may fix this issue.

diff --git a/mm/memory.c b/mm/memory.c
index 548d97e..90cea22 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3419,6 +3419,7 @@ static int do_shared_fault(struct mm_struct *mm,
struct vm_area_struct *vma,
  pgoff_t pgoff, unsigned int flags, pte_t orig_pte)
 {
  struct page *fault_page;
+ struct address_space *mapping;
  spinlock_t *ptl;
  pte_t *pte;
  int dirtied = 0;
@@ -3454,13 +3455,14 @@ static int do_shared_fault(struct mm_struct
*mm, struct vm_area_struct *vma,

  if (set_page_dirty(fault_page))
  dirtied = 1;
+ mapping = fault_page->mapping;
  unlock_page(fault_page);
- if ((dirtied || vma->vm_ops->page_mkwrite) && fault_page->mapping) {
+ if ((dirtied || vma->vm_ops->page_mkwrite) && mapping) {
  /*
  * Some device drivers do not set page.mapping but still
  * dirty their pages
  */
- balance_dirty_pages_ratelimited(fault_page->mapping);
+ balance_dirty_pages_ratelimited(mapping);
  }

  /* file_update_time outside page_lock */
--
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