From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752339AbeB1MPO (ORCPT ); Wed, 28 Feb 2018 07:15:14 -0500 Received: from foss.arm.com ([217.140.101.70]:48536 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752192AbeB1MPN (ORCPT ); Wed, 28 Feb 2018 07:15:13 -0500 From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: Mark Rutland , Andrew Morton , Ingo Molnar , Mathieu Desnoyers , Michal Hocko , Peter Zijlstra , Rik van Riel , Will Deacon Subject: [PATCH] Detect early free of a live mm Date: Wed, 28 Feb 2018 12:14:58 +0000 Message-Id: <20180228121458.2230-1-mark.rutland@arm.com> X-Mailer: git-send-email 2.11.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org KASAN splats indicate that in some cases we free a live mm, then continue to access it, with potentially disastrous results. This is likely due to a mismatched mmdrop() somewhere in the kernel, but so far the culprit remains elusive. Let's have __mmdrop() verify that the mm isn't live for the current task, similar to the existing check for init_mm. This way, we can catch this class of issue earlier, and without requiring KASAN. Signed-off-by: Mark Rutland Cc: Andrew Morton Cc: Ingo Molnar Cc: Mathieu Desnoyers Cc: Michal Hocko Cc: Peter Zijlstra Cc: Rik van Riel Cc: Will Deacon --- kernel/fork.c | 2 ++ 1 file changed, 2 insertions(+) Hi, For context, we're seeing an intermittent use-after-free of an mm on arm64 [1], where it looks like an mm has been freed earlier than expected. So far KASAN has only caught legitimate mmdrop() uses, where mm_count is presumably already bogus. Mark. [1] https://lkml.kernel.org/r/20180214120254.qq4w4s42ecxio7lu@lakrids.cambridge.arm.com diff --git a/kernel/fork.c b/kernel/fork.c index e5d9d405ae4e..6922d93551b8 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -595,6 +595,8 @@ static void check_mm(struct mm_struct *mm) void __mmdrop(struct mm_struct *mm) { BUG_ON(mm == &init_mm); + BUG_ON(mm == current->mm); + BUG_ON(mm == current->active_mm); mm_free_pgd(mm); destroy_context(mm); hmm_mm_destroy(mm); -- 2.11.0