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SubjectRe: mm: avoid null pointer access in vm_struct via /proc/vmallocinfo
Is this patch also relevant for the .32-stable tree?  I tried to
backport it, and only got one conflict, but I'm still not sure I got it
correct.

So, if someone wants this patch there, could they please provide me with
a backported version?

thanks,

greg k-h

On Mon, Oct 31, 2011 at 05:08:13PM -0700, Mitsuo Hayasaka wrote:
> From: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com>
>
> commit f5252e009d5b87071a919221e4f6624184005368 upstream.
>
> 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>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
>
> --- 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 5016f19..56faf31 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.


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