Commit de51257a authored Jul 30, 2010 by Hugh Dickins Committed by Linus Torvalds Jul 30, 2010

mm: fix ia64 crash when gcore reads gate area



Debian's ia64 autobuilders have been seeing kernel freeze or reboot
when running the gdb testsuite (Debian bug 588574): dannf bisected to
2.6.32 62eede62 "mm: ZERO_PAGE without
PTE_SPECIAL"; and reproduced it with gdb's gcore on a simple target.

I'd missed updating the gate_vma handling in __get_user_pages(): that
happens to use vm_normal_page() (nowadays failing on the zero page),
yet reported success even when it failed to get a page - boom when
access_process_vm() tried to copy that to its intermediate buffer.

Fix this, resisting cleanups: in particular, leave it for now reporting
success when not asked to get any pages - very probably safe to change,
but let's not risk it without testing exposure.

Why did ia64 crash with 16kB pages, but succeed with 64kB pages?
Because setup_gate() pads each 64kB of its gate area with zero pages.

Reported-by: Andreas Barth <aba@not.so.argh.org>
Bisected-by: dann frazier <dannf@debian.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Tested-by: dann frazier <dannf@dannf.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 51c20fcc

mm/memory.c

+13 −3

Original line number	Diff line number	Diff line
		@@ -1394,9 +1394,19 @@ int __get_user_pages(struct task_struct tsk, struct mm_struct mm,
		return i ? : -EFAULT;
		}
		if (pages) {
		struct page page = vm_normal_page(gate_vma, start, pte);
		struct page *page;

		page = vm_normal_page(gate_vma, start, *pte);
		if (!page) {
		if (!(gup_flags & FOLL_DUMP) &&
		is_zero_pfn(pte_pfn(*pte)))
		page = pte_page(*pte);
		else {
		pte_unmap(pte);
		return i ? : -EFAULT;
		}
		}
		pages[i] = page;
		if (page)
		get_page(page);
		}
		pte_unmap(pte);

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