Messages in this thread | | | Date | Thu, 3 Feb 2011 13:01:50 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] Huge TLB: Potential NULL deref in arch/x86/mm/hugetlbpage.c:huge_pmd_share() |
| |
On Thu, 3 Feb 2011 21:50:04 +0100 (CET) Jesper Juhl <jj@chaosbits.net> wrote:
> In arch/x86/mm/hugetlbpage.c:huge_pmd_share() we call find_vma(mm, addr) > and then subsequently dereference the pointer returned without checking if > it was NULL. I can't find anything that guarantees that find_vma() will > never return NULL in this case, so I believe there's a genuine bug. > However, I'd greatly appreciate it if someone would take the time to > double check me. > This patch implements what I believe to be the correct handling of a NULL > return from find_vma(). Please consider for inclusion. > > Signed-off-by: Jesper Juhl <jj@chaosbits.net> > --- > hugetlbpage.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c > index 069ce7c..0ebd3d0 100644 > --- a/arch/x86/mm/hugetlbpage.c > +++ b/arch/x86/mm/hugetlbpage.c > @@ -61,14 +61,19 @@ static int vma_shareable(struct vm_area_struct *vma, unsigned long addr) > static void huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) > { > struct vm_area_struct *vma = find_vma(mm, addr); > - struct address_space *mapping = vma->vm_file->f_mapping; > - pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) + > - vma->vm_pgoff; > + struct address_space *mapping; > + pgoff_t idx; > struct prio_tree_iter iter; > struct vm_area_struct *svma; > unsigned long saddr; > pte_t *spte = NULL; > > + if (!vma) > + return; > + > + mapping = vma->vm_file->f_mapping; > + idx = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; > + > if (!vma_shareable(vma, addr)) > return;
mmap_sem is held and the caller (copy_hugetlb_page_range) knows that the virtual address at `addr' is within a vma. So it's a "can't happen".
The code's all undocumented and you got fooled. Cause, effect.
| |