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SubjectRe: [PATCH] fix proc_reg_get_unmapped_area()
>>> 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



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