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Date: Fri, 31 Aug 2018 13:12:32 -0700 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: Greg Hackmann <ghackmann@...roid.com> Cc: linux-kernel@...r.kernel.org, Laura Abbott <labbott@...hat.com>, Sumit Semwal <sumit.semwal@...aro.org>, devel@...verdev.osuosl.org, kernel-team@...roid.com, Greg Hackmann <ghackmann@...gle.com>, stable@...r.kernel.org Subject: Re: [PATCH] staging: android: ion: fix ION_IOC_{MAP,SHARE} use-after-free 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
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