linux-kernel - Re: [PATCH v2] hugetlbfs: fix bug in pgoff overflow checking

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Date:   Mon, 2 Apr 2018 18:21:01 +0200
From:   Anders Roxell <anders.roxell@...aro.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nic Losby <blurbdust@...il.com>, Dan Rue <dan.rue@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] hugetlbfs: fix bug in pgoff overflow checking

On 30 March 2018 at 16:54, Mike Kravetz <mike.kravetz@...cle.com> wrote:
> This is a fix for a regression in 32 bit kernels caused by an
> invalid check for pgoff overflow in hugetlbfs mmap setup.  The
> check incorrectly specified that the size of a loff_t was the
> same as the size of a long.  The regression prevents mapping
> hugetlbfs files at offsets greater than 4GB on 32 bit kernels.
>
> On 32 bit kernels conversion from a page based unsigned long can
> not overflow a loff_t byte offset.  Therefore, skip this check
> if sizeof(unsigned long) != sizeof(loff_t).
>
> Fixes: 63489f8e8211 ("hugetlbfs: check for pgoff value overflow")
> Cc: <stable@...r.kernel.org>
> Reported-by: Dan Rue <dan.rue@...aro.org>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>

Tested-by: Anders Roxell <anders.roxell@...aro.org>

> ---
>  fs/hugetlbfs/inode.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index b9a254dcc0e7..d508c7844681 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -138,10 +138,14 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
>
>         /*
>          * page based offset in vm_pgoff could be sufficiently large to
> -        * overflow a (l)off_t when converted to byte offset.
> +        * overflow a loff_t when converted to byte offset.  This can
> +        * only happen on architectures where sizeof(loff_t) ==
> +        * sizeof(unsigned long).  So, only check in those instances.
>          */
> -       if (vma->vm_pgoff & PGOFF_LOFFT_MAX)
> -               return -EINVAL;
> +       if (sizeof(unsigned long) == sizeof(loff_t)) {
> +               if (vma->vm_pgoff & PGOFF_LOFFT_MAX)
> +                       return -EINVAL;
> +       }
>
>         /* must be huge page aligned */
>         if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))
> --
> 2.13.6
>