Commit 7b142d8f authored Jun 16, 2016 by Jann Horn Committed by Greg Kroah-Hartman Aug 15, 2016

android: binder: fix dangling pointer comparison



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.

v2: use the right refcounter

Fixes: a906d693 ("android: binder: Sanity check at binder ioctl")
Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Chen Feng <puck.chen@hisilicon.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 7ef9153d

drivers/android/binder.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -2962,6 +2962,7 @@ static int binder_open(struct inode nodp, struct file filp)
		return -ENOMEM;
		get_task_struct(current);
		proc->tsk = current;
		atomic_inc(&current->mm->mm_count);
		proc->vma_vm_mm = current->mm;
		INIT_LIST_HEAD(&proc->todo);
		init_waitqueue_head(&proc->wait);
		@@ -3167,6 +3168,7 @@ static void binder_deferred_release(struct binder_proc *proc)
		vfree(proc->buffer);
		}

		mmdrop(proc->vma_vm_mm);
		put_task_struct(proc->tsk);

		binder_debug(BINDER_DEBUG_OPEN_CLOSE,

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