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mm: avoid null pointer access in vm_struct via /proc/vmallocinfo

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.  This results in a null
pointer access and leads to a kernel panic.

Why this happens: In __vmalloc_node_range() called from vmalloc(), newly
allocated vm_struct is added to vmlist at __get_vm_area_node() and then,
some fields of vm_struct such as nr_pages and pages are set at
__vmalloc_area_node().  In other words, it is added to vmlist before it is
fully initialized.  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.

The patch adds the newly allocated vm_struct to the vmlist *after* it is
fully initialized.  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: David Rientjes <rientjes@google.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: <stable@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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1 parent 8c5fb8e commit f5252e009d5b87071a919221e4f6624184005368 Mitsuo Hayasaka committed with torvalds Nov 1, 2011
Showing with 49 additions and 17 deletions.
  1. +1 −0 include/linux/vmalloc.h
  2. +48 −17 mm/vmalloc.c
View
1 include/linux/vmalloc.h
@@ -13,6 +13,7 @@ struct vm_area_struct; /* vma defining user mapping in mm_types.h */
#define VM_MAP 0x00000004 /* vmap()ed pages */
#define VM_USERMAP 0x00000008 /* suitable for remap_vmalloc_range */
#define VM_VPAGES 0x00000010 /* buffer for pages was vmalloc'ed */
+#define VM_UNLIST 0x00000020 /* vm_struct is not listed in vmlist */
/* bits [20..32] reserved for arch specific ioremap internals */
/*
View
65 mm/vmalloc.c
@@ -1253,18 +1253,22 @@ EXPORT_SYMBOL_GPL(map_vm_area);
DEFINE_RWLOCK(vmlist_lock);
struct vm_struct *vmlist;
-static void insert_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
+static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
unsigned long flags, void *caller)
{
- struct vm_struct *tmp, **p;
-
vm->flags = flags;
vm->addr = (void *)va->va_start;
vm->size = va->va_end - va->va_start;
vm->caller = caller;
va->private = vm;
va->flags |= VM_VM_AREA;
+}
+
+static void insert_vmalloc_vmlist(struct vm_struct *vm)
+{
+ struct vm_struct *tmp, **p;
+ vm->flags &= ~VM_UNLIST;
write_lock(&vmlist_lock);
for (p = &vmlist; (tmp = *p) != NULL; p = &tmp->next) {
if (tmp->addr >= vm->addr)
@@ -1275,6 +1279,13 @@ static void insert_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
write_unlock(&vmlist_lock);
}
+static void insert_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
+ unsigned long flags, void *caller)
+{
+ setup_vmalloc_vm(vm, va, flags, caller);
+ insert_vmalloc_vmlist(vm);
+}
+
static struct vm_struct *__get_vm_area_node(unsigned long size,
unsigned long align, unsigned long flags, unsigned long start,
unsigned long end, int node, gfp_t gfp_mask, void *caller)
@@ -1313,7 +1324,18 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
return NULL;
}
- insert_vmalloc_vm(area, va, flags, caller);
+ /*
+ * When this function is called from __vmalloc_node_range,
+ * we do not add vm_struct to vmlist here to avoid
+ * accessing uninitialized members of vm_struct such as
+ * pages and nr_pages fields. They will be set later.
+ * To distinguish it from others, we use a VM_UNLIST flag.
+ */
+ if (flags & VM_UNLIST)
+ setup_vmalloc_vm(area, va, flags, caller);
+ else
+ insert_vmalloc_vm(area, va, flags, caller);
+
return area;
}
@@ -1381,17 +1403,20 @@ struct vm_struct *remove_vm_area(const void *addr)
va = find_vmap_area((unsigned long)addr);
if (va && va->flags & VM_VM_AREA) {
struct vm_struct *vm = va->private;
- struct vm_struct *tmp, **p;
- /*
- * remove from list and disallow access to this vm_struct
- * before unmap. (address range confliction is maintained by
- * vmap.)
- */
- write_lock(&vmlist_lock);
- for (p = &vmlist; (tmp = *p) != vm; p = &tmp->next)
- ;
- *p = tmp->next;
- write_unlock(&vmlist_lock);
+
+ if (!(vm->flags & VM_UNLIST)) {
+ struct vm_struct *tmp, **p;
+ /*
+ * remove from list and disallow access to
+ * this vm_struct before unmap. (address range
+ * confliction is maintained by vmap.)
+ */
+ write_lock(&vmlist_lock);
+ for (p = &vmlist; (tmp = *p) != vm; p = &tmp->next)
+ ;
+ *p = tmp->next;
+ write_unlock(&vmlist_lock);
+ }
vmap_debug_free_range(va->va_start, va->va_end);
free_unmap_vmap_area(va);
@@ -1602,15 +1627,21 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
if (!size || (size >> PAGE_SHIFT) > totalram_pages)
return NULL;
- area = __get_vm_area_node(size, align, VM_ALLOC, start, end, node,
- gfp_mask, caller);
+ area = __get_vm_area_node(size, align, VM_ALLOC | VM_UNLIST,
+ start, end, node, gfp_mask, caller);
if (!area)
return NULL;
addr = __vmalloc_area_node(area, gfp_mask, prot, node, caller);
/*
+ * In this function, newly allocated vm_struct is not added
+ * to vmlist at __get_vm_area_node(). so, it is added here.
+ */
+ insert_vmalloc_vmlist(area);
+
+ /*
* A ref_count = 3 is needed because the vm_struct and vmap_area
* structures allocated in the __get_vm_area_node() function contain
* references to the virtual address of the vmalloc'ed block.

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