linux-kernel - Re: [PATCH] mm/migrate: check for null vma before dereferencing it

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Message-Id: <20170411142633.d01ba0aaeb3e6075d517208c@linux-foundation.org>
Date:   Tue, 11 Apr 2017 14:26:33 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Colin King <colin.king@...onical.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>, Minchan Kim <minchan@...nel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-mm@...ck.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/migrate: check for null vma before dereferencing it

On Tue, 11 Apr 2017 13:51:02 +0100 Colin King <colin.king@...onical.com> wrote:

> From: Colin Ian King <colin.king@...onical.com>
> 
> check if vma is null before dereferencing it, this avoiding any
> potential null pointer dereferences on vma via the is_vm_hugetlb_page
> call or the direct vma->vm_flags reference.
> 
> Detected with CoverityScan, CID#1427995 ("Dereference before null check")
> 
> ...
>
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2757,10 +2757,10 @@ int migrate_vma(const struct migrate_vma_ops *ops,
>  	/* Sanity check the arguments */
>  	start &= PAGE_MASK;
>  	end &= PAGE_MASK;
> -	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL))
> -		return -EINVAL;
>  	if (!vma || !ops || !src || !dst || start >= end)
>  		return -EINVAL;
> +	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL))
> +		return -EINVAL;
>  	if (start < vma->vm_start || start >= vma->vm_end)
>  		return -EINVAL;
>  	if (end <= vma->vm_start || end > vma->vm_end)

I don't know what kernel version this is against but I don't think it's
anything recent?