linux-kernel - Re: [PATCH] hugetlbfs: Fix integer overflow check in hugetlbfs_file

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Message-ID: <65f4c60a-9534-56dc-099f-ee7a96e0ccaf@redhat.com>
Date:   Tue, 11 Jul 2023 13:49:06 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Linke Li <lilinke99@...mail.com>, linux-mm@...ck.org
Cc:     llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        trix@...hat.com, ndesaulniers@...gle.com, nathan@...nel.org,
        muchun.song@...ux.dev, mike.kravetz@...cle.com,
        Linke Li <lilinke99@...il.com>
Subject: Re: [PATCH] hugetlbfs: Fix integer overflow check in
 hugetlbfs_file_mmap()

On 10.07.23 10:32, 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;
> 
> The existing code includes an integer overflow check, which indicates
> that the variable len has the potential to overflow, leading to undefined
>   behavior according to the C standard. However, both GCC and Clang
> compilers may eliminate this overflow check based on the assumption
> that there will be no undefined behavior. Although the Linux kernel
> disables these optimizations by using the -fno-strict-overflow option,
> there is still a risk if the compilers make mistakes in the future.

So we're adding code to handle eventual future compiler bugs? That 
sounds wrong, but maybe I misunderstood the problem you are trying to solve?

-- 
Cheers,

David / dhildenb