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uprobes: Write_opcode()->__replace_page() can race with try_to_unmap()

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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>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120615154328.GA9571@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Oleg Nesterov 2012-06-15 17:43:28 +02:00 committed by Ingo Molnar
parent cc359d180f
commit 5323ce71e4
1 changed files with 13 additions and 28 deletions
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41
kernel/events/uprobes.c
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@ -129,33 +129,17 @@ 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;
return -EFAULT;
pgd = pgd_offset(mm, addr);
if (!pgd_present(*pgd))
goto out;
pud = pud_offset(pgd, addr);
if (!pud_present(*pud))
goto out;
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);
@ -174,10 +158,8 @@ 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;
}
/**
@ -222,9 +204,10 @@ 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:
/* Read the page with vaddr into memory */
ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &old_page, &vma);
if (ret <= 0)
@ -269,9 +252,9 @@ static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
/* poke the new insn in, ASSUMES we don't cross page boundary */
vaddr &= ~PAGE_MASK;
BUG_ON(vaddr + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
memcpy(vaddr_new + vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
pgoff = (vaddr & ~PAGE_MASK);
BUG_ON(pgoff + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
memcpy(vaddr_new + pgoff, &opcode, UPROBE_SWBP_INSN_SIZE);
kunmap_atomic(vaddr_new);
kunmap_atomic(vaddr_old);
@ -291,6 +274,8 @@ static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
put_out:
put_page(old_page);
if (unlikely(ret == -EAGAIN))
goto retry;
return ret;
}