lkml.org 
[lkml]   [2012]   [Jun]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 3/3] uprobes: write_opcode()->__replace_page() can race with try_to_unmap()

* Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote:

> > ---
> > Subject: [PATCH] uprobes: write_opcode()->__replace_page() can race with try_to_unmap()
> >
> > write_opcode() gets old_page via get_user_pages() and then calls
> > __replace_page() which assumes that this old_page is still mapped
> > after pte_offset_map_lock().
> >
> > This is not true if this old_page was already try_to_unmap()'ed,
> > and in this case everything __replace_page() does with old_page
> > is wrong. Just for example, put_page() is not balanced.
> >
> > I think it is possible to teach __replace_page() to handle this
> > unlikely case correctly, but this patch simply changes it to use
> > page_check_address() and return -EAGAIN if it fails. The caller
> > should notice this error code and retry.
> >
> > Note: write_opcode() asks for the cleanups, I'll try to do this
> > in a separate patch.
> >
> > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> > ---
> > kernel/events/uprobes.c | 41 +++++++++++++----------------------------
> > 1 files changed, 13 insertions(+), 28 deletions(-)
> >
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index 9c53bc2..54c8780 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -135,33 +135,17 @@ static loff_t vma_address(struct vm_area_struct *vma, loff_t offset)
> > static int __replace_page(struct vm_area_struct *vma, struct page *page, struct page *kpage)
> > {
> > struct mm_struct *mm = vma->vm_mm;
> > - pgd_t *pgd;
> > - pud_t *pud;
> > - pmd_t *pmd;
> > - pte_t *ptep;
> > - spinlock_t *ptl;
> > unsigned long addr;
> > - int err = -EFAULT;
> > + spinlock_t *ptl;
> > + pte_t *ptep;
> >
> > addr = page_address_in_vma(page, vma);
> > if (addr == -EFAULT)
> > - goto out;
> > -
> > - pgd = pgd_offset(mm, addr);
> > - if (!pgd_present(*pgd))
> > - goto out;
> > -
> > - pud = pud_offset(pgd, addr);
> > - if (!pud_present(*pud))
> > - goto out;
> > + return -EFAULT;
> >
> > - pmd = pmd_offset(pud, addr);
> > - if (!pmd_present(*pmd))
> > - goto out;
> > -
> > - ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
> > + ptep = page_check_address(page, mm, addr, &ptl, 0);
> > if (!ptep)
> > - goto out;
> > + return -EAGAIN;
> >
> > get_page(kpage);
> > page_add_new_anon_rmap(kpage, vma, addr);
> > @@ -180,10 +164,8 @@ static int __replace_page(struct vm_area_struct *vma, struct page *page, struct
> > try_to_free_swap(page);
> > put_page(page);
> > pte_unmap_unlock(ptep, ptl);
> > - err = 0;
> >
> > -out:
> > - return err;
> > + return 0;
> > }
> >
> > /**
> > @@ -228,9 +210,10 @@ static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
> > void *vaddr_old, *vaddr_new;
> > struct vm_area_struct *vma;
> > struct uprobe *uprobe;
> > + unsigned long pgoff;
> > loff_t addr;
> > int ret;
> > -
> > +retry:
>
> Just a check on coding style: Shouldnt we have a preceeding blank
> line before the goto label.

Yeah, that's most likely helpful to readability.

Thanks,

Ingo


\
 
 \ /
  Last update: 2012-06-15 15:01    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site