From: Roman Penyaev <rpenyaev@suse.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Joe Perches <joe@perches.com>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH 1/3] mm/vmalloc: fix size check for remap_vmalloc_range_partial()
Date: Fri, 04 Jan 2019 12:06:44 +0100 [thread overview]
Message-ID: <c41a065f04c89d0a1f0312b1b4fa7b1e@suse.de> (raw)
In-Reply-To: <20190103145954.16942-2-rpenyaev@suse.de>
Hi Andrew,
Could you please update the commit message with something as
the following (I hope it will become a bit clearer now):
-------------
When VM_NO_GUARD is not set area->size includes adjacent guard page,
thus for correct size checking get_vm_area_size() should be used,
but not area->size.
This fixes possible kernel oops when userspace tries to mmap an area
on 1 page bigger than was allocated by vmalloc_user() call: the size
check inside remap_vmalloc_range_partial() accounts non-existing
guard page also, so check successfully passes but vmalloc_to_page()
returns NULL (guard page does not physically exist).
The following code pattern example should trigger an oops:
static int oops_mmap(struct file *file, struct vm_area_struct *vma)
{
void *mem;
mem = vmalloc_user(4096);
BUG_ON(!mem);
/* Do not care about mem leak */
return remap_vmalloc_range(vma, mem, 0);
}
And userspace simply mmaps size + PAGE_SIZE:
mmap(NULL, 8192, PROT_WRITE|PROT_READ, MAP_PRIVATE, fd, 0);
Possible candidates for oops which do not have any explicit size
checks:
*** drivers/media/usb/stkwebcam/stk-webcam.c:
v4l_stk_mmap[789] ret = remap_vmalloc_range(vma, sbuf->buffer, 0);
Or the following one:
*** drivers/video/fbdev/core/fbmem.c
static int
fb_mmap(struct file *file, struct vm_area_struct * vma)
...
res = fb->fb_mmap(info, vma);
Where fb_mmap callback calls remap_vmalloc_range() directly without
any explicit checks:
*** drivers/video/fbdev/vfb.c
static int vfb_mmap(struct fb_info *info,
struct vm_area_struct *vma)
{
return remap_vmalloc_range(vma, (void *)info->fix.smem_start,
vma->vm_pgoff);
}
--------
--
Roman
On 2019-01-03 15:59, Roman Penyaev wrote:
> area->size can include adjacent guard page but get_vm_area_size()
> returns actual size of the area.
>
> This fixes possible kernel crash when userspace tries to map area
> on 1 page bigger: size check passes but the following vmalloc_to_page()
> returns NULL on last guard (non-existing) page.
>
> Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Joe Perches <joe@perches.com>
> Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Cc: stable@vger.kernel.org
> ---
> mm/vmalloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 871e41c55e23..2cd24186ba84 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2248,7 +2248,7 @@ int remap_vmalloc_range_partial(struct
> vm_area_struct *vma, unsigned long uaddr,
> if (!(area->flags & VM_USERMAP))
> return -EINVAL;
>
> - if (kaddr + size > area->addr + area->size)
> + if (kaddr + size > area->addr + get_vm_area_size(area))
> return -EINVAL;
>
> do {
next prev parent reply other threads:[~2019-01-04 11:06 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190103145954.16942-1-rpenyaev@suse.de>
2019-01-03 14:59 ` [PATCH 1/3] mm/vmalloc: fix size check for remap_vmalloc_range_partial() Roman Penyaev
2019-01-03 15:13 ` Michal Hocko
2019-01-03 19:27 ` Roman Penyaev
2019-01-03 19:40 ` Michal Hocko
2019-01-03 20:31 ` Roman Penyaev
2019-01-04 9:38 ` Michal Hocko
2019-01-04 10:21 ` Roman Penyaev
2019-01-04 10:28 ` Michal Hocko
2019-01-03 19:59 ` Michal Hocko
2019-01-04 11:06 ` Roman Penyaev [this message]
2019-01-11 19:19 ` Andrey Ryabinin
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