From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0C46C04AAF for ; Mon, 20 May 2019 12:28:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 79A4E216E3 for ; Mon, 20 May 2019 12:28:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558355317; bh=4MqpRGZefz7Um9TTQzbpqPbOnyQLQcMfqVf5dEROAJ4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=DQR+iPzYa5eqcer2zrOybcO2J7eCeZLjNij3m1Jp64VWeb8hKuAaYYBrwi75N1mXY mwVgq36uu8HlTjWyaSOuZJZefv/h5JZ/1V0zV1UCiotqRu/Bpp81qs0uyCYGaxF7p9 OYSG10PUDHWqYOW3V7w3smGrIHV66+mR22l4paP0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389705AbfETM2f (ORCPT ); Mon, 20 May 2019 08:28:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:44366 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389693AbfETM2d (ORCPT ); Mon, 20 May 2019 08:28:33 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F0EA620645; Mon, 20 May 2019 12:28:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558355312; bh=4MqpRGZefz7Um9TTQzbpqPbOnyQLQcMfqVf5dEROAJ4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=hV+GHCdLW0fTy8JH9ylG3YoOM5xyn6EVs2j/wMP8cPGaCw/Li0ypnd5RZn46yAE9O pnAWO8buj0JrxMG2XogOGzzhZ3wA1v7n7gVWG4k7CSIj+ZELTk+55HQu9nfg+bukxj erEFIOr2vhjWtB62vlRI/vUh+1Xm7/7VFIsNpWfg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Andrea Arcangeli , zhong jiang , syzbot+cbb52e396df3e565ab02@syzkaller.appspotmail.com, Oleg Nesterov , Jann Horn , Hugh Dickins , Mike Rapoport , Mike Kravetz , Peter Xu , Jason Gunthorpe , "Kirill A . Shutemov" , Michal Hocko , Andrew Morton , Linus Torvalds Subject: [PATCH 5.0 072/123] userfaultfd: use RCU to free the task struct when fork fails Date: Mon, 20 May 2019 14:14:12 +0200 Message-Id: <20190520115249.634554502@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190520115245.439864225@linuxfoundation.org> References: <20190520115245.439864225@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Andrea Arcangeli commit c3f3ce049f7d97cc7ec9c01cb51d9ec74e0f37c2 upstream. The task structure is freed while get_mem_cgroup_from_mm() holds rcu_read_lock() and dereferences mm->owner. get_mem_cgroup_from_mm() failing fork() ---- --- task = mm->owner mm->owner = NULL; free(task) if (task) *task; /* use after free */ The fix consists in freeing the task with RCU also in the fork failure case, exactly like it always happens for the regular exit(2) path. That is enough to make the rcu_read_lock hold in get_mem_cgroup_from_mm() (left side above) effective to avoid a use after free when dereferencing the task structure. An alternate possible fix would be to defer the delivery of the userfaultfd contexts to the monitor until after fork() is guaranteed to succeed. Such a change would require more changes because it would create a strict ordering dependency where the uffd methods would need to be called beyond the last potentially failing branch in order to be safe. This solution as opposed only adds the dependency to common code to set mm->owner to NULL and to free the task struct that was pointed by mm->owner with RCU, if fork ends up failing. The userfaultfd methods can still be called anywhere during the fork runtime and the monitor will keep discarding orphaned "mm" coming from failed forks in userland. This race condition couldn't trigger if CONFIG_MEMCG was set =n at build time. [aarcange@redhat.com: improve changelog, reduce #ifdefs per Michal] Link: http://lkml.kernel.org/r/20190429035752.4508-1-aarcange@redhat.com Link: http://lkml.kernel.org/r/20190325225636.11635-2-aarcange@redhat.com Fixes: 893e26e61d04 ("userfaultfd: non-cooperative: Add fork() event") Signed-off-by: Andrea Arcangeli Tested-by: zhong jiang Reported-by: syzbot+cbb52e396df3e565ab02@syzkaller.appspotmail.com Cc: Oleg Nesterov Cc: Jann Horn Cc: Hugh Dickins Cc: Mike Rapoport Cc: Mike Kravetz Cc: Peter Xu Cc: Jason Gunthorpe Cc: "Kirill A . Shutemov" Cc: Michal Hocko Cc: zhong jiang Cc: syzbot+cbb52e396df3e565ab02@syzkaller.appspotmail.com Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- kernel/fork.c | 31 +++++++++++++++++++++++++++++-- 1 file changed, 29 insertions(+), 2 deletions(-) --- a/kernel/fork.c +++ b/kernel/fork.c @@ -953,6 +953,15 @@ static void mm_init_aio(struct mm_struct #endif } +static __always_inline void mm_clear_owner(struct mm_struct *mm, + struct task_struct *p) +{ +#ifdef CONFIG_MEMCG + if (mm->owner == p) + WRITE_ONCE(mm->owner, NULL); +#endif +} + static void mm_init_owner(struct mm_struct *mm, struct task_struct *p) { #ifdef CONFIG_MEMCG @@ -1332,6 +1341,7 @@ static struct mm_struct *dup_mm(struct t free_pt: /* don't put binfmt in mmput, we haven't got module yet */ mm->binfmt = NULL; + mm_init_owner(mm, NULL); mmput(mm); fail_nomem: @@ -1663,6 +1673,21 @@ static inline void rcu_copy_process(stru #endif /* #ifdef CONFIG_TASKS_RCU */ } +static void __delayed_free_task(struct rcu_head *rhp) +{ + struct task_struct *tsk = container_of(rhp, struct task_struct, rcu); + + free_task(tsk); +} + +static __always_inline void delayed_free_task(struct task_struct *tsk) +{ + if (IS_ENABLED(CONFIG_MEMCG)) + call_rcu(&tsk->rcu, __delayed_free_task); + else + free_task(tsk); +} + /* * This creates a new process as a copy of the old one, * but does not actually start it yet. @@ -2124,8 +2149,10 @@ bad_fork_cleanup_io: bad_fork_cleanup_namespaces: exit_task_namespaces(p); bad_fork_cleanup_mm: - if (p->mm) + if (p->mm) { + mm_clear_owner(p->mm, p); mmput(p->mm); + } bad_fork_cleanup_signal: if (!(clone_flags & CLONE_THREAD)) free_signal_struct(p->signal); @@ -2156,7 +2183,7 @@ bad_fork_cleanup_count: bad_fork_free: p->state = TASK_DEAD; put_task_stack(p); - free_task(p); + delayed_free_task(p); fork_out: spin_lock_irq(¤t->sighand->siglock); hlist_del_init(&delayed.node);