[ 10/47] ARM: prevent VM_GROWSDOWN mmaps extending below FIRST_USER_ADDRESS

[Greg KH <gregkh@linuxfoundation.org>]

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

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

From: Russell King <rmk+kernel@arm.linux.org.uk>

commit 9b61a4d1b2064dbd0c9e61754305ac852170509f upstream.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arm/mm/fault.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -245,7 +245,9 @@ good_area:
 	return handle_mm_fault(mm, vma, addr & PAGE_MASK, flags);
 
 check_stack:
-	if (vma->vm_flags & VM_GROWSDOWN && !expand_stack(vma, addr))
+	/* Don't allow expansion below FIRST_USER_ADDRESS */
+	if (vma->vm_flags & VM_GROWSDOWN &&
+	    addr >= FIRST_USER_ADDRESS && !expand_stack(vma, addr))
 		goto good_area;
 out:
 	return fault;