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Subject[PATCH 5.0 110/238] mm/vmalloc: fix size check for remap_vmalloc_range_partial()
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Roman Penyaev <rpenyaev@suse.de>

commit 401592d2e095947344e10ec0623adbcd58934dd4 upstream.

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);
}

Link: http://lkml.kernel.org/r/20190103145954.16942-2-rpenyaev@suse.de
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Acked-by: 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: <stable@vger.kernel.org>
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@linuxfoundation.org>

---
mm/vmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2248,7 +2248,7 @@ int remap_vmalloc_range_partial(struct v
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 {

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