[PATCH v2] binder: fix proc->files use-after-free

Todd Kjos tkjos at android.com
Thu Nov 16 20:37:02 UTC 2017

Sorry about that, do you want a v3 with correct annotations?

On Thu, Nov 16, 2017 at 12:27 PM, Greg KH <gregkh at linuxfoundation.org> wrote:
> On Thu, Nov 16, 2017 at 09:56:50AM -0800, Todd Kjos wrote:
>> proc->files cleanup is initiated by binder_vma_close. Therefore
>> a reference on the binder_proc is not enough to prevent the
>> files_struct from being released while the binder_proc still has
>> a reference. This can lead to an attempt to dereference the
>> stale pointer obtained from proc->files prior to proc->files
>> cleanup. This has been seen once in task_get_unused_fd_flags()
>> when __alloc_fd() is called with a stale "files".
>> The fix is to always use get_files_struct() to obtain struct_files
>> so that the refcount on the files_struct is used to prevent
>> a premature free. proc->files is removed since we get it every
>> time.
>> Signed-off-by: Todd Kjos <tkjos at google.com>
>> ---
>>  drivers/android/binder.c | 63 +++++++++++++++++++++++-------------------------
>>  1 file changed, 30 insertions(+), 33 deletions(-)
> For a v2 patch (or v3 or whatever), you need to put below the --- line
> what changed from the previous version(s).
> Documentation/SubmittingPatches describes this pretty well :)
> thanks,
> greg k-h

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