[PATCH RESEND] android: binder: Sanity check at binder ioctl

From: Chen Feng
Date: Mon Jan 18 2016 - 22:50:10 EST

When a process fork a child process, we should not allow the
child process use the binder which opened by parent process.

But if the binder-object creater is a thread of one process who exit,
the other thread can also use this binder-object normally.
We can distinguish this by the member proc->tsk->mm.
If the thread exit the tsk->mm will be NULL.

proc->tsk->mm != current->mm && proc->tsk->mm

So only allow the shared mm_struct to use the same binder-object and
check the existence of mm_struct.

Signed-off-by: Chen Feng <puck.chen@xxxxxxxxxxxxx>
Signed-off-by: Wei Dong <weidong2@xxxxxxxxxxxxx>
Signed-off-by: Junmin Zhao <zhaojunmin@xxxxxxxxxx>
Reviewed-by: Zhuangluan Su <suzhuangluan@xxxxxxxxxxxxx>
drivers/android/binder.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index a39e85f..279063c 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2736,6 +2736,8 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)

/*pr_info("binder_ioctl: %d:%d %x %lx\n",
proc->pid, current->pid, cmd, arg);*/
+ if (unlikely(proc->tsk->mm != current->mm && proc->tsk->mm))
+ return -EINVAL;

trace_binder_ioctl(cmd, arg);