Messages in this thread | | | Date | Tue, 19 Jan 2016 14:40:59 -0800 (PST) | From | David Rientjes <> | Subject | Re: [PATCH v2] android: binder: Sanity check at binder ioctl |
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On Tue, 19 Jan 2016, Chen Feng wrote:
> 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. >
Why does exit_mm(), the point where tsk->mm == NULL, signify the point at which the binder can now be used by other threads?
> 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. > > V2: Fix compile error for error commit > > Signed-off-by: Chen Feng <puck.chen@hisilicon.com> > Signed-off-by: Wei Dong <weidong2@hisilicon.com> > Signed-off-by: Junmin Zhao <zhaojunmin@huawei.com> > Reviewed-by: Zhuangluan Su <suzhuangluan@hisilicon.com> > --- > 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); >
I would imagine that you would want to do READ_ONCE(proc->tsk->mm) so you are guaranteed to be testing the same value.
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