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-Tag: firefly_0821_release~9142^2~23
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=c0dab5ce4fc28c2a21edce5fa1edcb2b45eb2064;p=firefly-linux-kernel-4.4.55.git

ARM: prevent VM_GROWSDOWN mmaps extending below FIRST_USER_ADDRESS

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>
---

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index bc0e1d88fd3b..8799eae5da9b 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -266,7 +266,9 @@ good_area:
 	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;