On Fri, Aug 31, 2018 at 01:17:20PM -0700, Greg Hackmann wrote:
On 08/31/2018 01:12 PM, Greg Kroah-Hartman wrote:
On Fri, Aug 31, 2018 at 01:06:27PM -0700, Greg Hackmann wrote:
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