On Wed, Jun 15, 2016 at 3:09 PM, Jann Horn <jannh@xxxxxxxxxx> wrote: > If /dev/binder is opened and the opener process then e.g. calls execve, > proc->vma_vm_mm will still point to the location of the now-freed > mm_struct. If the process then calls ioctl(binder_fd, ...), the dangling > proc->vma_vm_mm pointer will be compared to current->mm. > > Let the binder take a reference to the mm_struct to avoid this. > > In the current code, the BUG_ON() will never trigger; it's just there > in case someone changes the conditions under which get_task_mm() can > fail. Just WARN_ON() wouldn't work because of the mmput(), and I don't > want to complicate the code with a dead error handling code path. > (If the BUG_ON() is unacceptable, I'd replace the get_task_mm() with > a direct refcount increment or just omit the BUG_ON().) > > This shouldn't cause additional memory usage in a well-behaved system > because you're not supposed to keep binder fds open over fork() or > execve(). > > Fixes: a906d6931f3ccaf7de805643190765ddd7378e27 > Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> > --- > drivers/android/binder.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/drivers/android/binder.c b/drivers/android/binder.c > index 16288e7..4e9131d 100644 > --- a/drivers/android/binder.c > +++ b/drivers/android/binder.c > @@ -2962,7 +2962,8 @@ static int binder_open(struct inode *nodp, struct file *filp) > return -ENOMEM; > get_task_struct(current); > proc->tsk = current; > - proc->vma_vm_mm = current->mm; > + proc->vma_vm_mm = get_task_mm(current); > + BUG_ON(proc->vma_vm_mm == NULL); > INIT_LIST_HEAD(&proc->todo); > init_waitqueue_head(&proc->wait); > proc->default_priority = task_nice(current); > @@ -3167,6 +3168,7 @@ static void binder_deferred_release(struct binder_proc *proc) > vfree(proc->buffer); > } > > + mmput(proc->vma_vm_mm); > put_task_struct(proc->tsk); > > binder_debug(BINDER_DEBUG_OPEN_CLOSE, > -- > 2.8.0.rc3.226.g39d4020 > Does this work? In the past, holding a reference to a task's mm while the driver is open would prevent vma close which in turn would prevent release of the fd. -- Arve Hjønnevåg _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
