linux-kernel - Re: [PATCH] fix proc_reg_get_unmapped

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Date:	Thu, 17 Oct 2013 10:16:26 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"HATAYAMA Daisuke" <d.hatayama@...fujitsu.com>
Cc:	<davem@...emloft.net>, <adobriyan@...il.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fix proc_reg_get_unmapped_area()

>>> On 17.10.13 at 10:36, HATAYAMA Daisuke <d.hatayama@...fujitsu.com> wrote:
> (2013/10/17 16:23), Jan Beulich wrote:
>>>>> On 16.10.13 at 22:40, Andrew Morton <akpm@...ux-foundation.org> wrote:
>>> On Wed, 16 Oct 2013 12:32:40 +0100 "Jan Beulich" <JBeulich@...e.com> wrote:
>>>
>>>> Commit c4fe24485729fc2cbff324c111e67a1cc2f9adea ("sparc: fix PCI device
>>>> proc file mmap(2)"), while fixing one problem, introduced two new ones:
>>>> - the function truncates the return value from ->get_unmapped_area() on
>>>>    64-bit architectures,
>>>> - _all_ descendants are now required to set .get_unmapped_area to non-
>>>>    NULL, which wasn't necessary before (and shouldn't be).
>>>>
>>>> Both - afaict - are a result from a too simplistic copy'n'paste from
>>>> proc_reg_mmap() done in that change.
>>>>
>>>> This likely also addresses reports like the one at
>>>>
>>> 
> http://linux-kernel.2935.n7.nabble.com/mmap-for-proc-vmcore-broken-since-3-12-rc1-td729 
> 
>>> 326.html.
>>>>
>>>> ...
>>>>
>>>> --- 3.12-rc5/fs/proc/inode.c
>>>> +++ 3.12-rc5-proc-get-unmapped-area/fs/proc/inode.c
>>>> @@ -288,12 +288,12 @@ static int proc_reg_mmap(struct file *fi
>>>>   static unsigned long proc_reg_get_unmapped_area(struct file *file, 
> unsigned
>>> long orig_addr, unsigned long len, unsigned long pgoff, unsigned long flags)
>>>>   {
>>>>   	struct proc_dir_entry *pde = PDE(file_inode(file));
>>>> -	int rv = -EIO;
>>>> -	unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned
>>> long, unsigned long, unsigned long);
>>>> +	unsigned long rv = -EIO;
>>>> +
>>>>   	if (use_pde(pde)) {
>>>> -		get_unmapped_area = pde->proc_fops->get_unmapped_area;
>>>> -		if (get_unmapped_area)
>>>> -			rv = get_unmapped_area(file, orig_addr, len, pgoff, flags);
>>>> +		rv = (pde->proc_fops->get_unmapped_area
>>>> +		      ?: current->mm->get_unmapped_area)(file, orig_addr, len,
>>>> +							 pgoff, flags);
>>>>   		unuse_pde(pde);
>>>>   	}
>>>>   	return rv;
>>>
>>> I think these two patches will address the problems:
>>>
>>> http://ozlabs.org/~akpm/mmots/broken-out/procfs-fix-unintended-truncation-of-retur 
>>> ned-mapped-address.patch
>>> http://ozlabs.org/~akpm/mmots/broken-out/procfs-call-default-get_unmapped_area-on- 
>>> mmu-present-architectures.patch
>>>
>>> I'll be sending those Linuswards today.  Please check them.  (I think
>>> your version would break the nommu build).
>>
>> Yes indeed - I did search for existing patches, but didn't find them.
>> I see Linus merged them already, so there's no point anymore
>> sending Reviewed-by tags.
>>
>> I think though that in the !MMU case the second of them leaves an
>> issue unfixed nevertheless: If the specific procfs handler has no
>> .get_unmapped_area, the operation would still fail in that case
>> rather than succeed as it did before that wrapper got added.)
>>
>> Jan
>>
> 
> Yes, there remains difference on no-mmu that if mmap is not defined, mmap() 
> now returns
> EIO, it should return ENODEV.

No, afaict it should succeed (and simply use the address that came in).

Jan

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