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SubjectRe: [PATCH] fix proc_reg_get_unmapped_area()
(2013/10/17 16:23), Jan Beulich wrote:
>>>> On 16.10.13 at 22:40, Andrew Morton <akpm@linux-foundation.org> wrote:
>> On Wed, 16 Oct 2013 12:32:40 +0100 "Jan Beulich" <JBeulich@suse.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.

In mm/nommu.c,

/* eliminate any capabilities that we can't support on this
* device */
if (!file->f_op->get_unmapped_area)
capabilities &= ~BDI_CAP_MAP_DIRECT;

and

*/
if (capabilities & BDI_CAP_MAP_DIRECT) {
addr = file->f_op->get_unmapped_area(file, addr, len,
pgoff, flags);
if (IS_ERR_VALUE(addr)) {
ret = addr;
if (ret != -ENOSYS)
goto error_just_free;

/* the driver refused to tell us where to site
* the mapping so we'll have to attempt to copy
* it */
ret = -ENODEV;
if (!(capabilities & BDI_CAP_MAP_COPY))
goto error_just_free;

capabilities &= ~BDI_CAP_MAP_DIRECT;
} else {
vma->vm_start = region->vm_start = addr;
vma->vm_end = region->vm_end = addr + len;
}
}

So, how about let proc_reg_get_unmapped_area() return ENOSYS, not EIO?

--
Thanks.
HATAYAMA, Daisuke



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