On Fri, Aug 31, 2018 at 01:17:20PM -0700, Greg Hackmann wrote:

On 08/31/2018 01:12 PM, Greg Kroah-Hartman wrote:

quoted

On Fri, Aug 31, 2018 at 01:06:27PM -0700, Greg Hackmann wrote:

quoted

The ION_IOC_{MAP,SHARE} ioctls drop and reacquire client->lock several
times while operating on one of the client's ion_handles.  This creates
windows where userspace can call ION_IOC_FREE on the same client with
the same handle, and effectively make the kernel drop its own reference.
For example:

- thread A: ION_IOC_ALLOC creates an ion_handle with refcount 1
- thread A: starts ION_IOC_MAP and increments the refcount to 2
- thread B: ION_IOC_FREE decrements the refcount to 1
- thread B: ION_IOC_FREE decrements the refcount to 0 and frees the
            handle
- thread A: continues ION_IOC_MAP with a dangling ion_handle * to
            freed memory

Fix this by holding client->lock for the duration of
ION_IOC_{MAP,SHARE}, preventing the concurrent ION_IOC_FREE.  Also
remove ion_handle_get_by_id(), since there's literally no way to use it
safely.

This patch is applied on top of 4.9.y.  Kernels 4.12 and later are
unaffected, since all the underlying ion_handle infrastructure has been
ripped out.

Does 4.4.y or older also need this?  If so, can you send backports, as
this one does not apply there.

thanks,

greg k-h

Yes, 4.4.y and older will need this.  If there are no objections to this
patch, I'll send backports ASAP.

None from me, thanks!

greg k-h