Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932773Ab2FBQyh (ORCPT ); Sat, 2 Jun 2012 12:54:37 -0400 Received: from mail-pz0-f46.google.com ([209.85.210.46]:34381 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759618Ab2FBQyg (ORCPT ); Sat, 2 Jun 2012 12:54:36 -0400 From: Siddhesh Poyarekar To: linux-kernel@vger.kernel.org Cc: Oleg Nesterov , Tejun Heo , Andrew Morton , David Howells , "Eric W. Biederman" , Siddhesh Poyarekar Subject: [PATCH] Avoid dereferencing a possibly NULL mm Date: Sat, 2 Jun 2012 22:24:22 +0530 Message-Id: <1338656062-25008-1-git-send-email-siddhesh.poyarekar@gmail.com> X-Mailer: git-send-email 1.7.7.6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1192 Lines: 42 The NULL check for mm in exit_mm occurs after mm_release is called. This looks wrong because mm_release dereferences mm: ... if (!(tsk->flags & PF_SIGNALED) && atomic_read(&mm->mm_users) > 1) { /* ... This dereference seems unsafe and hence is fixed by moving the NULL check above mm_release. Signed-off-by: Siddhesh Poyarekar --- kernel/exit.c | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index 34867cc..15fe63c 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -640,9 +640,11 @@ static void exit_mm(struct task_struct * tsk) struct mm_struct *mm = tsk->mm; struct core_state *core_state; - mm_release(tsk, mm); if (!mm) return; + + mm_release(tsk, mm); + /* * Serialize with any possible pending coredump. * We must hold mmap_sem around checking core_state -- 1.7.7.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/