Messages in this thread Patch in this message | | | From | Mitsuo Hayasaka <> | Subject | [PATCH v2] avoid null pointer access in vm_struct | Date | Fri, 19 Aug 2011 19:51:33 +0900 |
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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;
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