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

[Andrew Morton]

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

> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> 
> 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?