Commit c517ee74 authored Jul 29, 2012 by Oleg Nesterov Committed by Ingo Molnar Jul 30, 2012

uprobes: __replace_page() should not use page_address_in_vma()



page_address_in_vma(old_page) in __replace_page() is ugly and
wrong. The caller already knows the correct virtual address,
this page was found by get_user_pages(vaddr).

However, page_address_in_vma() can actually fail if
page->mapping was cleared by __delete_from_page_cache() after
get_user_pages() returns. But this means the race with page
reclaim, write_opcode() should not fail, it should retry and
read this page again. Probably the race with remove_mapping() is
not possible due to page_freeze_refs() logic, but afaics at
least shmem_writepage()->shmem_delete_from_page_cache() can
clear ->mapping.

We could change __replace_page() to return -EAGAIN in this case,
but it would be better to simply use the caller's vaddr and rely
on page_check_address().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar.vnet.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20120729182216.GA20311@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent f403072c

kernel/events/uprobes.c

+4 −7

Original line number	Diff line number	Diff line
		@@ -127,22 +127,19 @@ static loff_t vma_address(struct vm_area_struct *vma, loff_t offset)
		* based on replace_page in mm/ksm.c
		*
		* @vma: vma that holds the pte pointing to page
		* @addr: address the old @page is mapped at
		* @page: the cowed page we are replacing by kpage
		* @kpage: the modified page we replace page by
		*
		* Returns 0 on success, -EFAULT on failure.
		*/
		static int __replace_page(struct vm_area_struct vma, struct page page, struct page *kpage)
		static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
		struct page page, struct page kpage)
		{
		struct mm_struct *mm = vma->vm_mm;
		unsigned long addr;
		spinlock_t *ptl;
		pte_t *ptep;

		addr = page_address_in_vma(page, vma);
		if (addr == -EFAULT)
		return -EFAULT;

		ptep = page_check_address(page, mm, addr, &ptl, 0);
		if (!ptep)
		return -EAGAIN;
		@@ -243,7 +240,7 @@ retry:
		goto unlock_out;

		lock_page(new_page);
		ret = __replace_page(vma, old_page, new_page);
		ret = __replace_page(vma, vaddr, old_page, new_page);
		unlock_page(new_page);

		unlock_out:

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