[patch 10/24] futexes: Fix infinite loop in get_futex_key() on huge page

[Greg KH]

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

------------------

From: Sonny Rao <sonnyrao@xxxxxxxxxx>

commit ce2ae53b750abfaa012ce408e93da131a5b5649b upstream.

get_futex_key() can infinitely loop if it is called on a
virtual address that is within a huge page but not aligned to
the beginning of that page.  The call to get_user_pages_fast
will return the struct page for a sub-page within the huge page
and the check for page->mapping will always fail.

The fix is to call compound_head on the page before checking
that it's mapped.

Signed-off-by: Sonny Rao <sonnyrao@xxxxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: anton@xxxxxxxxx
Cc: rajamony@xxxxxxxxxx
Cc: speight@xxxxxxxxxx
Cc: mstephen@xxxxxxxxxx
Cc: grimm@xxxxxxxxxx
Cc: mikey@xxxxxxxxxxxxxxxxx
LKML-Reference: <20090710231313.GA23572@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 kernel/futex.c |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -241,6 +241,7 @@ again:
 	if (err < 0)
 		return err;
 
+	page = compound_head(page);
 	lock_page(page);
 	if (!page->mapping) {
 		unlock_page(page);


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