linux-kernel - [PATCH 1/3] mm/vmalloc: fix size check for remap_vmalloc_range

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Date:   Thu,  3 Jan 2019 15:59:52 +0100
From:   Roman Penyaev <rpenyaev@...e.de>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Roman Penyaev <rpenyaev@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Joe Perches <joe@...ches.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH 1/3] mm/vmalloc: fix size check for remap_vmalloc_range_partial()

area->size can include adjacent guard page but get_vm_area_size()
returns actual size of the area.

This fixes possible kernel crash when userspace tries to map area
on 1 page bigger: size check passes but the following vmalloc_to_page()
returns NULL on last guard (non-existing) page.

Signed-off-by: Roman Penyaev <rpenyaev@...e.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc: Joe Perches <joe@...ches.com>
Cc: "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org
---
 mm/vmalloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 871e41c55e23..2cd24186ba84 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2248,7 +2248,7 @@ int remap_vmalloc_range_partial(struct vm_area_struct *vma, unsigned long uaddr,
 	if (!(area->flags & VM_USERMAP))
 		return -EINVAL;
 
-	if (kaddr + size > area->addr + area->size)
+	if (kaddr + size > area->addr + get_vm_area_size(area))
 		return -EINVAL;
 
 	do {
-- 
2.19.1