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Message-ID: <20230720184148.GA3899@monkey>
Date: Thu, 20 Jul 2023 11:41:48 -0700
From: Mike Kravetz <mike.kravetz@...cle.com>
To: Linke Li <lilinke99@...mail.com>
Cc: linux-mm@...ck.org, muchun.song@...ux.dev, nathan@...nel.org,
ndesaulniers@...gle.com, trix@...hat.com,
linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
dan.carpenter@...aro.org, Linke Li <lilinke99@...il.com>
Subject: Re: [PATCH v3] hugetlbfs: Fix integer overflow check in
hugetlbfs_file_mmap()
On 07/20/23 22:49, Linke Li wrote:
> From: Linke Li <lilinke99@...il.com>
>
> ```
> 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;
> ```
>
> There is a signed integer overflow in the code, which is undefined
> behavior according to the C stacnard. Although this works, it's
> still a bit ugly and static checkers will complain.
>
> Using macro "check_add_overflow" to do the overflow check can
> effectively detect integer overflow and avoid any undefined behavior.
>
> Signed-off-by: Linke Li <lilinke99@...il.com>
> ---
> v3: fix checkpatch warning and better description.
> fs/hugetlbfs/inode.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 7b17ccfa039d..326a8c0af5f6 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -154,10 +154,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
> if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))
> return -EINVAL;
>
> - vma_len = (loff_t)(vma->vm_end - vma->vm_start);
I don't think you wanted to delete the above line as ...
> - len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
> - /* check for overflow */
> - if (len < vma_len)
> + if (check_add_overflow(vma_len, (loff_t)vma->vm_pgoff << PAGE_SHIFT, &len))
.. vma_len is uninitialized here.
> return -EINVAL;
>
> inode_lock(inode);
> --
> 2.25.1
>
--
Mike Kravetz
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