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 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
