linux-kernel - [PATCH v2] avoid null pointer access in vm

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Date:	Fri, 19 Aug 2011 19:51:33 +0900
From:	Mitsuo Hayasaka <mitsuo.hayasaka.hu@...achi.com>
To:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	yrl.pp-manager.tt@...achi.com,
	Mitsuo Hayasaka <mitsuo.hayasaka.hu@...achi.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Namhyung Kim <namhyung@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: [PATCH v2] avoid null pointer access in vm_struct

The /proc/vmallocinfo shows information about vmalloc allocations in vmlist
that is a linklist of vm_struct. It, however, may access pages field of
vm_struct where a page was not allocated, which results in a null pointer
access and leads to a kernel panic.

Why this happen:
In __vmalloc_area_node(), the nr_pages field of vm_struct are set to the
expected number of pages to be allocated, before the actual pages
allocations. At the same time, when the /proc/vmallocinfo is read, it
accesses the pages field of vm_struct according to the nr_pages field at
show_numa_info(). Thus, a null pointer access happens.

Patch:
This patch sets nr_pages field of vm_struct AFTER the pages allocations
finished in __vmalloc_area_node(). So, it can avoid accessing the pages
field with unallocated page when show_numa_info() is called.

Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@...achi.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Namhyung Kim <namhyung@...il.com>
Cc: David Rientjes <rientjes@...gle.com>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---

 mm/vmalloc.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 7ef0903..49d8aed 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1529,7 +1529,6 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	nr_pages = (area->size - PAGE_SIZE) >> PAGE_SHIFT;
 	array_size = (nr_pages * sizeof(struct page *));
 
-	area->nr_pages = nr_pages;
 	/* Please note that the recursion is strictly bounded. */
 	if (array_size > PAGE_SIZE) {
 		pages = __vmalloc_node(array_size, 1, nested_gfp|__GFP_HIGHMEM,
@@ -1538,15 +1537,15 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 	} else {
 		pages = kmalloc_node(array_size, nested_gfp, node);
 	}
-	area->pages = pages;
-	area->caller = caller;
-	if (!area->pages) {
+	if (!pages) {
 		remove_vm_area(area->addr);
 		kfree(area);
 		return NULL;
 	}
+	area->pages = pages;
+	area->caller = caller;
 
-	for (i = 0; i < area->nr_pages; i++) {
+	for (i = 0; i < nr_pages; i++) {
 		struct page *page;
 		gfp_t tmp_mask = gfp_mask | __GFP_NOWARN;
 
@@ -1562,6 +1561,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 		}
 		area->pages[i] = page;
 	}
+	area->nr_pages = nr_pages;
 
 	if (map_vm_area(area, prot, &pages))
 		goto fail;

--
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