[ 46/53] ARM: prevent VM_GROWSDOWN mmaps extending below FIRST_USER_ADDRESS

[Ben Hutchings]

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

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

From: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>

commit 9b61a4d1b2064dbd0c9e61754305ac852170509f upstream.

Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/arm/mm/fault.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- linux.orig/arch/arm/mm/fault.c
+++ linux/arch/arm/mm/fault.c
@@ -267,7 +267,9 @@
 	return fault;
 
 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;


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