Re: mm: NULL ptr deref in unlink_file_vma

["Kirill A. Shutemov" <kirill@shutemov.name>]

[ fixed Davidlohr's address. ]

On Mon, Dec 22, 2014 at 08:01:02PM +0200, Kirill A. Shutemov wrote:
> On Mon, Dec 22, 2014 at 10:04:02AM -0500, Sasha Levin wrote:
> > Hi all,
> > 
> > While fuzzing with trinity inside a KVM tools guest running the latest -next
> > kernel, I've stumbled on the following spew:
> > 
> > [  432.376425] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
> > [  432.378876] IP: down_write (./arch/x86/include/asm/rwsem.h:105 ./arch/x86/include/asm/rwsem.h:121 kernel/locking/rwsem.c:71)
> 
> Looks like vma->vm_file->mapping is NULL. Somebody freed ->vm_file from
> under us?
> 
> I suspect Davidlohr's patchset on i_mmap_lock, but I cannot find any code
> path which could lead to the crash.
> 
> I've noticed one strange code path, which probably is not related to the
> issue:
> 
> unmap_mapping_range()
>   i_mmap_lock_read(mapping);
>   unmap_mapping_range_tree()
>     unmap_mapping_range_vma()
>       zap_page_range_single()
>         unmap_single_vma()
> 	  if (unlikely(is_vm_hugetlb_page(vma))) {
> 	    i_mmap_lock_write(vma->vm_file->f_mapping);
> 
> Is it legal to down_write() semaphore while we have it taken on read?
> It must be the same mapping, right?
> 
> > [  432.380085] PGD 57e5e0067 PUD 57e5e1067 PMD 0
> > [  432.380085] Oops: 0002 [#1] PREEMPT SMP KASAN
> > [  432.380085] Dumping ftrace buffer:
> > [  432.380085]    (ftrace buffer empty)
> > [  432.380085] Modules linked in:
> > [  432.380085] CPU: 4 PID: 9249 Comm: trinity-subchil Not tainted 3.18.0-next-20141219-sasha-00047-gaab33f6-dirty #1627
> > [  432.380085] task: ffff8806a88c8000 ti: ffff880664f3c000 task.ti: ffff880664f3c000
> > [  432.380085] RIP: down_write (./arch/x86/include/asm/rwsem.h:105 ./arch/x86/include/asm/rwsem.h:121 kernel/locking/rwsem.c:71)
> > [  432.380085] RSP: 0018:ffff880664f3fc98  EFLAGS: 00010292
> > [  432.380085] RAX: 0000000000000038 RBX: ffff880101aa7c00 RCX: 1ffff10020354f8f
> > [  432.380085] RDX: ffffffff00000001 RSI: 1ffff100fe326200 RDI: 0000000000000038
> > [  432.380085] RBP: ffff880664f3fcb8 R08: 0000000000000000 R09: ffff880101aa6258
> > [  432.380085] R10: 0000000000000000 R11: 0000000000000000 R12: ffff880000025900
> > [  432.380085] R13: 0000000000000038 R14: 0000000000000000 R15: ffff880101aa7c00
> > [  432.380085] FS:  00007f21149c4700(0000) GS:ffff880216400000(0000) knlGS:0000000000000000
> > [  432.380085] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > [  432.380085] CR2: 0000000000000038 CR3: 000000057a4f3000 CR4: 00000000000006a0
> > [  432.380085] Stack:
> > [  432.380085]  ffff880101aa7c00 ffff880101aa7c78 ffff880101aa6200 ffff880101aa7c00
> > [  432.380085]  ffff880664f3fce8 ffffffffa1953e9d[  432.400920] CONFIG_KASAN_INLINE enabled
> > [  432.400923] GPF could be caused by NULL-ptr deref or user memory access
> > 
> > [  432.402566]  ffff880101aa7c00 00007f210f9f3000
> > [  432.402566]  dfffe90000000000 ffff880101aa4600 ffff880664f3fd48 ffffffffa1937821
> > [  432.402566] Call Trace:
> > [  432.402566] unlink_file_vma (mm/mmap.c:264)
> > [  432.402566] free_pgtables (mm/memory.c:548)
> > [  432.402566] exit_mmap (mm/mmap.c:2846)
> > [  432.402566] ? kmem_cache_free (mm/slub.c:2712 mm/slub.c:2721)
> > [  432.402566] mmput (kernel/fork.c:659)
> > [  432.402566] do_exit (./arch/x86/include/asm/thread_info.h:164 kernel/exit.c:438 kernel/exit.c:732)
> > [  432.402566] ? preempt_count_sub (kernel/sched/core.c:2620)
> > [  432.402566] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63)
> > [  432.402566] do_group_exit (include/linux/sched.h:775 kernel/exit.c:858)
> > [  432.402566] SyS_exit_group (kernel/exit.c:886)
> > [  432.402566] system_call_fastpath (arch/x86/kernel/entry_64.S:423)
> > [ 432.402566] Code: 79 05 e8 f9 e9 a6 f2 5d c3 0f 1f 80 00 00 00 00 66 66 66 66 90 48 ba 01 00 00 00 ff ff ff ff 55 48 89 f8 48 89 e5 53 48 83 ec 18 <f0> 48 0f c1 10 85 d2 74 05 e8 f7 e9 a6 f2 65 48 8b 1c 25 80 b9
> > All code
> > ========
> >    0:	79 05                	jns    0x7
> >    2:	e8 f9 e9 a6 f2       	callq  0xfffffffff2a6ea00
> >    7:	5d                   	pop    %rbp
> >    8:	c3                   	retq
> >    9:	0f 1f 80 00 00 00 00 	nopl   0x0(%rax)
> >   10:	66 66 66 66 90       	data32 data32 data32 xchg %ax,%ax
> >   15:	48 ba 01 00 00 00 ff 	movabs $0xffffffff00000001,%rdx
> >   1c:	ff ff ff
> >   1f:	55                   	push   %rbp
> >   20:	48 89 f8             	mov    %rdi,%rax
> >   23:	48 89 e5             	mov    %rsp,%rbp
> >   26:	53                   	push   %rbx
> >   27:	48 83 ec 18          	sub    $0x18,%rsp
> >   2b:*	f0 48 0f c1 10       	lock xadd %rdx,(%rax)		<-- trapping instruction
> >   30:	85 d2                	test   %edx,%edx
> >   32:	74 05                	je     0x39
> >   34:	e8 f7 e9 a6 f2       	callq  0xfffffffff2a6ea30
> >   39:	65                   	gs
> >   3a:	48                   	rex.W
> >   3b:	8b                   	.byte 0x8b
> >   3c:	1c 25                	sbb    $0x25,%al
> >   3e:	80                   	.byte 0x80
> >   3f:	b9                   	.byte 0xb9
> > 	...
> > 
> > Code starting with the faulting instruction
> > ===========================================
> >    0:	f0 48 0f c1 10       	lock xadd %rdx,(%rax)
> >    5:	85 d2                	test   %edx,%edx
> >    7:	74 05                	je     0xe
> >    9:	e8 f7 e9 a6 f2       	callq  0xfffffffff2a6ea05
> >    e:	65                   	gs
> >    f:	48                   	rex.W
> >   10:	8b                   	.byte 0x8b
> >   11:	1c 25                	sbb    $0x25,%al
> >   13:	80                   	.byte 0x80
> >   14:	b9                   	.byte 0xb9
> > 	...
> > [  432.402566] RIP down_write (./arch/x86/include/asm/rwsem.h:105 ./arch/x86/include/asm/rwsem.h:121 kernel/locking/rwsem.c:71)
> > [  432.402566]  RSP <ffff880664f3fc98>
> > [  432.402566] CR2: 0000000000000038
> > 
> > 
> > Thanks,
> > Sasha
> > --
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> 
> -- 
>  Kirill A. Shutemov
> 
> --
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-- 
 Kirill A. Shutemov

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