Re: [PATCH] fix proc_reg_get_unmapped_area()

[HATAYAMA Daisuke]

(2013/10/17 16:23), Jan Beulich wrote:
> > > > On 16.10.13 at 22:40, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > On Wed, 16 Oct 2013 12:32:40 +0100 "Jan Beulich" <JBeulich@xxxxxxxx> 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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