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>

2 files changed, 49 insertions, 17 deletions

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 9332e52ea8c2..687fb11e2010 100644
--- a/include/linux/vmalloc.h
+++ b/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 */
 
 /*
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5016f19e1661..56faf3163ee2 100644
--- a/mm/vmalloc.c
+++ b/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);
@@ -1602,8 +1627,8 @@ 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;
@@ -1611,6 +1636,12 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
         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.