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* Re: [PATCH] mm: mmap: Fix general protection fault in unlink_file_vma()
@ 2020-10-08  7:17 linmiaohe
  2020-10-09  4:23 ` Andrew Morton
  0 siblings, 1 reply; 6+ messages in thread
From: linmiaohe @ 2020-10-08  7:17 UTC (permalink / raw)
  To: Andrew Morton; +Cc: linux-mm, linux-kernel

Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 16 Sep 2020 05:07:33 -0400 Miaohe Lin <linmiaohe@huawei.com> wrote:
>
>> The syzbot reported the below general protection fault:
>> 
>> general protection fault, probably for non-canonical address
>> 0xe00eeaee0000003b: 0000 [#1] PREEMPT SMP KASAN
>> KASAN: maybe wild-memory-access in range 
>> [0x00777770000001d8-0x00777770000001df]
>> CPU: 1 PID: 10488 Comm: syz-executor721 Not tainted 
>> 5.9.0-rc3-syzkaller #0
>> Trace:
>>  free_pgtables+0x1b3/0x2f0 mm/memory.c:415
>>  exit_mmap+0x2c0/0x530 mm/mmap.c:3184
>>  __mmput+0x122/0x470 kernel/fork.c:1076
>> 
>> It's because the ->mmap() callback can change vma->vm_file and fput 
>> the original file. But the commit d70cec898324 ("mm: mmap: merge vma 
>> after
>> call_mmap() if possible") failed to catch this case and always fput() 
>> the original file, hence add an extra fput().
>> 
>> ...
>>
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -1815,7 +1815,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>>  			merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags,
>>  				NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX);
>>  			if (merge) {
>> -				fput(file);
>> +				/* ->mmap() can change vma->vm_file and fput the original file. So
>> +				 * fput the vma->vm_file here or we would add an extra fput for file
>> +				 * and cause general protection fault ultimately.
>> +				 */
>> +				fput(vma->vm_file);
>>  				vm_area_free(vma);
>>  				vma = merge;
>>  				/* Update vm_flags and possible addr to pick up the change. We 
>> don't
>
>What about the case where this code block does its `goto unmap_writable'?
>
>	/* Once vma denies write, undo our temporary denial count */
>	if (file) {
>unmap_writable:
>		if (vm_flags & VM_SHARED)
>			mapping_unmap_writable(file->f_mapping);
>		if (vm_flags & VM_DENYWRITE)
>			allow_write_access(file);
>	}
>	file = vma->vm_file;
>
>is this using the correct file?  I think it is, but please do check.
>

Many thanks for your reply.

Yes, I think so too. We do deny_write_access and mapping_map_writable on @file, so we should undo all of this on @file.
Since @file is unchanged over the second vma_merge() time, we'are using the correct @file to undo our temporary denial count.

But how should I check this explicitly ? I can't find out a way to do this. Could you please figure it out for me?
Thanks again.



^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH] mm: mmap: Fix general protection fault in unlink_file_vma()
@ 2020-10-09  6:39 linmiaohe
  0 siblings, 0 replies; 6+ messages in thread
From: linmiaohe @ 2020-10-09  6:39 UTC (permalink / raw)
  To: Andrew Morton; +Cc: linux-mm, linux-kernel

Andrew Morton <akpm@linux-foundation.org> wrote:
> On Thu, 8 Oct 2020 07:17:18 +0000 linmiaohe <linmiaohe@huawei.com> wrote:
>
>> Andrew Morton <akpm@linux-foundation.org> wrote:
>> > On Wed, 16 Sep 2020 05:07:33 -0400 Miaohe Lin <linmiaohe@huawei.com> wrote:
>> >
>> >> The syzbot reported the below general protection fault:
>>
>> >
>> >is this using the correct file?  I think it is, but please do check.
>> >
>> 
>> Many thanks for your reply.
>> 
>> Yes, I think so too. We do deny_write_access and mapping_map_writable on @file, so we should undo all of this on @file.
>> Since @file is unchanged over the second vma_merge() time, we'are using the correct @file to undo our temporary denial count.
>> 
>> But how should I check this explicitly ? I can't find out a way to do this. Could you please figure it out for me?
>
>I meant "please check (review) the code as it now is", not "please add a check" ;)
>

Oh, I see. I have reviewed the code carefully. The @file should be right one as I explained in previous email. ;)

Have a good day! ^_^



^ permalink raw reply	[flat|nested] 6+ messages in thread
* Re: [PATCH] mm: mmap: Fix general protection fault in unlink_file_vma()
@ 2020-10-07  2:51 linmiaohe
  0 siblings, 0 replies; 6+ messages in thread
From: linmiaohe @ 2020-10-07  2:51 UTC (permalink / raw)
  To: akpm; +Cc: linux-mm, linux-kernel

Friendly ping.
> The syzbot reported the below general protection fault:
>
> general protection fault, probably for non-canonical address
> 0xe00eeaee0000003b: 0000 [#1] PREEMPT SMP KASAN
> KASAN: maybe wild-memory-access in range [0x00777770000001d8-0x00777770000001df]
> CPU: 1 PID: 10488 Comm: syz-executor721 Not tainted 5.9.0-rc3-syzkaller #0
>
> It's because the ->mmap() callback can change vma->vm_file and fput the original file. But the commit d70cec898324 ("mm: mmap: merge vma after
> call_mmap() if possible") failed to catch this case and always fput() the original file, hence add an extra fput().
>
> [ Thanks Hillf for pointing this extra fput() out. ]
>
> @@ -1815,7 +1815,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>  			merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags,
>  				NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX);
>  			if (merge) {
> -				fput(file);
> +				/* ->mmap() can change vma->vm_file and fput the original file. So
> +				 * fput the vma->vm_file here or we would add an extra fput for file
> +				 * and cause general protection fault ultimately.
> +				 */
> +				fput(vma->vm_file);
>  				vm_area_free(vma);
>  				vma = merge;
>  				/* Update vm_flags and possible addr to pick up the change. We don't
> --
> 2.19.1
>


^ permalink raw reply	[flat|nested] 6+ messages in thread
* [PATCH] mm: mmap: Fix general protection fault in unlink_file_vma()
@ 2020-09-16  9:07 Miaohe Lin
  2020-10-07 19:04 ` Andrew Morton
  0 siblings, 1 reply; 6+ messages in thread
From: Miaohe Lin @ 2020-09-16  9:07 UTC (permalink / raw)
  To: akpm; +Cc: linux-mm, linux-kernel, linmiaohe

The syzbot reported the below general protection fault:

general protection fault, probably for non-canonical address
0xe00eeaee0000003b: 0000 [#1] PREEMPT SMP KASAN
KASAN: maybe wild-memory-access in range
[0x00777770000001d8-0x00777770000001df]
CPU: 1 PID: 10488 Comm: syz-executor721 Not tainted 5.9.0-rc3-syzkaller #0
RIP: 0010:unlink_file_vma+0x57/0xb0 mm/mmap.c:164
Code: 4c 8b a5 a0 00 00 00 4d 85 e4 74 4e e8 92 d7 cd ff 49 8d bc 24
d8 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c
02 00 75 3d 4d 8b b4 24 d8 01 00 00 4d 8d 6e 78 4c 89 ef e8
RSP: 0018:ffffc9000ac0f9b0 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff88800010ceb0 RCX: ffffffff81592421
RDX: 000eeeee0000003b RSI: ffffffff81a6736e RDI: 00777770000001d8
RBP: ffff88800010ceb0 R08: 0000000000000001 R09: ffff88801291a50f
R10: ffffed10025234a1 R11: 0000000000000001 R12: 0077777000000000
R13: 00007f1eea0da000 R14: 00007f1eea0d9000 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8880ae700000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1eea11a9d0 CR3: 000000000007e000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 free_pgtables+0x1b3/0x2f0 mm/memory.c:415
 exit_mmap+0x2c0/0x530 mm/mmap.c:3184
 __mmput+0x122/0x470 kernel/fork.c:1076
 mmput+0x53/0x60 kernel/fork.c:1097
 exit_mm kernel/exit.c:483 [inline]
 do_exit+0xa8b/0x29f0 kernel/exit.c:793
 do_group_exit+0x125/0x310 kernel/exit.c:903
 get_signal+0x428/0x1f00 kernel/signal.c:2757
 arch_do_signal+0x82/0x2520 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:136 [inline]
 exit_to_user_mode_prepare+0x1ae/0x200 kernel/entry/common.c:167
 syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:242
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

It's because the ->mmap() callback can change vma->vm_file and fput the
original file. But the commit d70cec898324 ("mm: mmap: merge vma after
call_mmap() if possible") failed to catch this case and always fput() the
original file, hence add an extra fput().

[ Thanks Hillf for pointing this extra fput() out. ]

Fixes: d70cec898324 ("mm: mmap: merge vma after call_mmap() if possible")
Reported-by: syzbot+c5d5a51dcbb558ca0cb5@syzkaller.appspotmail.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/mmap.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index e3a1c1b48909..37c985850dc6 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1815,7 +1815,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 			merge = vma_merge(mm, prev, vma->vm_start, vma->vm_end, vma->vm_flags,
 				NULL, vma->vm_file, vma->vm_pgoff, NULL, NULL_VM_UFFD_CTX);
 			if (merge) {
-				fput(file);
+				/* ->mmap() can change vma->vm_file and fput the original file. So
+				 * fput the vma->vm_file here or we would add an extra fput for file
+				 * and cause general protection fault ultimately.
+				 */
+				fput(vma->vm_file);
 				vm_area_free(vma);
 				vma = merge;
 				/* Update vm_flags and possible addr to pick up the change. We don't
-- 
2.19.1



^ permalink raw reply related	[flat|nested] 6+ messages in thread
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2020-10-08  7:17 [PATCH] mm: mmap: Fix general protection fault in unlink_file_vma() linmiaohe
2020-10-09  4:23 ` Andrew Morton
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2020-10-09  6:39 linmiaohe
2020-10-07  2:51 linmiaohe
2020-09-16  9:07 Miaohe Lin
2020-10-07 19:04 ` Andrew Morton

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