[PATCH v2] avoid null pointer access in vm_struct

Mitsuo Hayasaka
2011-08-19T10:46:46Z

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@hitachi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.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;