[02/34] mm: fix ia64 crash when gcore reads gate area

From: Greg KH
Date: Fri Aug 06 2010 - 15:14:55 EST

2.6.32-stable review patch. If anyone has any objections, please let us know.


From: Hugh Dickins <hughd@xxxxxxxxxx>

commit de51257aa301652876ab6e8f13ea4eadbe4a3846 upstream.

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 62eede62dafb4a6633eae7ffbeb34c60dba5e7b1 "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@xxxxxxxxxxxxxxx>
Bisected-by: dann frazier <dannf@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Tested-by: dann frazier <dannf@xxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

mm/memory.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1282,10 +1282,20 @@ int __get_user_pages(struct task_struct
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);
+ get_page(page);
if (vmas)

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/