Re: [PATCH] fix proc_reg_get_unmapped_area()

[Andrew Morton]

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-td729326.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-returned-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).

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