Re: [PATCH] Modify the check condition

[Peter Zijlstra]

On Sat, Sep 18, 2021 at 06:52:32AM +0000, cgel.zte@xxxxxxxxx wrote:
> From: Yang Guang <yang.guang5@xxxxxxxxxx>
> 
> The vma may be NULL, and accessing the member of vma like "vma->vm_start"
> in calling follow_phys may occur segmentation fault.
> So it should check vma at beginning. If vma is null, it will return. And
> the if condition won't execute "vm->vm_flags".
> 
> Signed-off-by: Yang Guang <yang.guang5@xxxxxxxxxx>
> ---
>  arch/x86/mm/pat/memtype.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c
> index 4ba2a3ee4bce..b7108b37b754 100644
> --- a/arch/x86/mm/pat/memtype.c
> +++ b/arch/x86/mm/pat/memtype.c
> @@ -1089,7 +1089,7 @@ void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
>  	resource_size_t paddr;
>  	unsigned long prot;
>  
> -	if (vma && !(vma->vm_flags & VM_PAT))
> +	if (!(vma) || !(vma->vm_flags & VM_PAT))
>  		return;

Yet another braindead patch that shows you don't actually understand C.