Messages in this thread |  | | Subject | Re: [PATCH] hugetlbfs: fix offset overflow in huegtlbfs mmap | From | Mike Kravetz <> | Date | Sat, 15 Apr 2017 15:58:59 -0700 |
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On 04/13/2017 08:32 PM, Naoya Horiguchi wrote: > On Tue, Apr 11, 2017 at 03:51:58PM -0700, Mike Kravetz wrote: > ... >> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c >> index 7163fe0..dde8613 100644 >> --- a/fs/hugetlbfs/inode.c >> +++ b/fs/hugetlbfs/inode.c >> @@ -136,17 +136,26 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma) >> vma->vm_flags |= VM_HUGETLB | VM_DONTEXPAND; >> vma->vm_ops = &hugetlb_vm_ops; >> >> + /* >> + * Offset passed to mmap (before page shift) could have been >> + * negative when represented as a (l)off_t. >> + */ >> + if (((loff_t)vma->vm_pgoff << PAGE_SHIFT) < 0) >> + return -EINVAL; >> + >> if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT)) >> return -EINVAL; >> >> vma_len = (loff_t)(vma->vm_end - vma->vm_start); >> + len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT); >> + /* check for overflow */ >> + if (len < vma_len) >> + return -EINVAL; > > Andrew sent this patch to Linus today, so I know it's a little too late, but > I think that getting len directly from vma like below might be a simpler fix. > > len = (loff_t)(vma->vm_end - vma->vm_start + (vma->vm_pgoff << PAGE_SHIFT)); > > This shouldn't overflow because vma->vm_{end|start|pgoff} are unsigned long, > but if worried you can add VM_BUG_ON_VMA(len < 0, vma).
Thanks Naoya,
I am pretty sure the checks are necessary. You are correct in that vma->vm_{end|start|pgoff} are unsigned long. However, pgoff can be a REALLY big value that becomes negative when shifted.
Note that pgoff is simply the off_t offset value passed from the user cast to unsigned long and shifted right by PAGE_SHIFT. There is nothing to prevent a user from passing a 'signed' negative value. In the reproducer provided, the value passed from user space is 0x8000000000000000ULL.
-- Mike Kravetz
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