Re: [PATCH] mm: fix NULL ptr deref when walking hugepages

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Wed, May 23, 2012 at 09:20:43AM +0200, Sasha Levin wrote:
> A missing vlidation of the value returned by find_vma() could cause a NULL ptr
> dereference when walking the pagetable.
> 
> This is triggerable from usermode by a simple user by trying to read a
> page info out of /proc/pid/pagemap which doesn't exist.
> 
> Introduced by commit 025c5b24 ("thp: optimize away unnecessary page table
> locking").
> 
> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
> ---
>  fs/proc/task_mmu.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 3e564f0..885830b 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -820,7 +820,7 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>  
>  	/* find the first VMA at or above 'addr' */
>  	vma = find_vma(walk->mm, addr);
> -	if (pmd_trans_huge_lock(pmd, vma) == 1) {
> +	if (vma && pmd_trans_huge_lock(pmd, vma) == 1) {
>  		for (; addr != end; addr += PAGE_SIZE) {
>  			unsigned long offset;
>  
> -- 

Thank you. I have no objection.

Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

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