Re: [PATCH v3 3/6] android: binder: Move buffer out of area shared with user space

[Dan Carpenter]

On Tue, Aug 29, 2017 at 05:46:59PM -0700, Sherry Yang wrote:
> Binder driver allocates buffer meta data in a region that is mapped
> in user space. These meta data contain pointers in the kernel.
> 
> This patch allocates buffer meta data on the kernel heap that is
> not mapped in user space, and uses a pointer to refer to the data mapped.
> 
> Also move alloc->buffers initialization from mmap to init since it's
> now used even when mmap failed or was not called.
> 
> Signed-off-by: Sherry Yang <sherryy@xxxxxxxxxxx>
> ---

The difference between v2 and v3 is that we've shifted some
initialization around to fix the crashing bug that kbuild found.  You
should not that difference here under the --- cut off.

>  drivers/android/binder_alloc.c          | 146 +++++++++++++++++++-------------
>  drivers/android/binder_alloc.h          |   2 +-
>  drivers/android/binder_alloc_selftest.c |  11 ++-
>  3 files changed, 91 insertions(+), 68 deletions(-)

But really we still need to have some answers or discussion about the
questions that Greg and I raised.  Greg asked if the other Android devs
had Acked this.  Please ping Arve to Ack this.

I was curious about the security impact or why we were writing this
patch 3/6.  It seems we are fixing an information disclosure bug.  Or is
it something worse than that?  Or have I misunderstood entirely.

We probably original put the buffers in userspace for accounting reasons
so we could kill programs that used too much RAM.  This patch doesn't
create a problem with that hopefully?  We're just moving the metadata to
kernel space?

regards,
dan carpenter