[PATCH 090/241] s390/gup: add missing TASK_SIZE check to get_user_pages_fast()

[Herton Ronaldo Krzesinski]

3.5.7.2 -stable review patch.  If anyone has any objections, please let me know.

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

From: Heiko Carstens <heiko.carstens at de.ibm.com>

commit d55c4c613fc4d4ad2ba0fc6fa2b57176d420f7e4 upstream.

When walking page tables we need to make sure that everything
is within bounds of the ASCE limit of the task's address space.
Otherwise we might calculate e.g. a pud pointer which is not
within a pud and dereference it.
So check against TASK_SIZE (which is the ASCE limit) before
walking page tables.

Reviewed-by: Gerald Schaefer <gerald.schaefer at de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens at de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 arch/s390/mm/gup.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/mm/gup.c b/arch/s390/mm/gup.c
index 65cb06e..4ccf9f5 100644
--- a/arch/s390/mm/gup.c
+++ b/arch/s390/mm/gup.c
@@ -183,7 +183,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	addr = start;
 	len = (unsigned long) nr_pages << PAGE_SHIFT;
 	end = start + len;
-	if (end < start)
+	if ((end < start) || (end > TASK_SIZE))
 		goto slow_irqon;
 
 	/*
-- 
1.7.9.5