From: Russell King <rmk+kernel@arm.linux.org.uk>
Date: Wed, 16 May 2012 14:19:20 +0000 (+0100)
Subject: ARM: prevent VM_GROWSDOWN mmaps extending below FIRST_USER_ADDRESS
X-Git-Url: http://git.alex.org.uk

ARM: prevent VM_GROWSDOWN mmaps extending below FIRST_USER_ADDRESS

Cc: <stable@vger.kernel.org>
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index f074675..5bb4835 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -247,7 +247,9 @@ 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;