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=-6.5 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 6D98AC352A4 for ; Wed, 12 Feb 2020 14:27:00 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id CCECA20873 for ; Wed, 12 Feb 2020 14:26:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CCECA20873 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-17788-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 1420 invoked by uid 550); 12 Feb 2020 14:26:53 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 1376 invoked from network); 12 Feb 2020 14:26:52 -0000 Date: Wed, 12 Feb 2020 15:26:38 +0100 From: Alexey Gladkov To: Al Viro Cc: LKML , Kernel Hardening , Linux API , Linux FS Devel , Linux Security Module , Akinobu Mita , Alexey Dobriyan , Andrew Morton , Andy Lutomirski , Daniel Micay , Djalal Harouni , "Dmitry V . Levin" , "Eric W . Biederman" , Greg Kroah-Hartman , Ingo Molnar , "J . Bruce Fields" , Jeff Layton , Jonathan Corbet , Kees Cook , Linus Torvalds , Oleg Nesterov , Solar Designer Subject: Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances Message-ID: <20200212142637.dhcrgy252qw6eg42@comp-core-i7-2640m-0182e6> Mail-Followup-To: Al Viro , LKML , Kernel Hardening , Linux API , Linux FS Devel , Linux Security Module , Akinobu Mita , Alexey Dobriyan , Andrew Morton , Andy Lutomirski , Daniel Micay , Djalal Harouni , "Dmitry V . Levin" , "Eric W . Biederman" , Greg Kroah-Hartman , Ingo Molnar , "J . Bruce Fields" , Jeff Layton , Jonathan Corbet , Kees Cook , Linus Torvalds , Oleg Nesterov , Solar Designer References: <20200210150519.538333-1-gladkov.alexey@gmail.com> <20200210150519.538333-8-gladkov.alexey@gmail.com> <20200211224553.GK23230@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200211224553.GK23230@ZenIV.linux.org.uk> On Tue, Feb 11, 2020 at 10:45:53PM +0000, Al Viro wrote: > On Mon, Feb 10, 2020 at 04:05:15PM +0100, Alexey Gladkov wrote: > > This allows to flush dcache entries of a task on multiple procfs mounts > > per pid namespace. > > > > The RCU lock is used because the number of reads at the task exit time > > is much larger than the number of procfs mounts. > > > > Cc: Kees Cook > > Cc: Andy Lutomirski > > Signed-off-by: Djalal Harouni > > Suggested-by: Linus Torvalds > > Signed-off-by: Alexey Gladkov > > --- > > fs/proc/base.c | 20 +++++++++++++++----- > > fs/proc/root.c | 27 ++++++++++++++++++++++++++- > > include/linux/pid_namespace.h | 2 ++ > > include/linux/proc_fs.h | 2 ++ > > 4 files changed, 45 insertions(+), 6 deletions(-) > > > > diff --git a/fs/proc/base.c b/fs/proc/base.c > > index 4ccb280a3e79..24b7c620ded3 100644 > > --- a/fs/proc/base.c > > +++ b/fs/proc/base.c > > @@ -3133,7 +3133,7 @@ static const struct inode_operations proc_tgid_base_inode_operations = { > > .permission = proc_pid_permission, > > }; > > > > -static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid) > > +static void proc_flush_task_mnt_root(struct dentry *mnt_root, pid_t pid, pid_t tgid) > > { > > struct dentry *dentry, *leader, *dir; > > char buf[10 + 1]; > > @@ -3142,7 +3142,7 @@ static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid) > > name.name = buf; > > name.len = snprintf(buf, sizeof(buf), "%u", pid); > > /* no ->d_hash() rejects on procfs */ > > - dentry = d_hash_and_lookup(mnt->mnt_root, &name); > > + dentry = d_hash_and_lookup(mnt_root, &name); > > if (dentry) { > > d_invalidate(dentry); > ... which can block > > dput(dentry); > ... and so can this > > > + rcu_read_lock(); > > + list_for_each_entry_rcu(fs_info, &upid->ns->proc_mounts, pidns_entry) { > > + mnt_root = fs_info->m_super->s_root; > > + proc_flush_task_mnt_root(mnt_root, upid->nr, tgid->numbers[i].nr); > > ... making that more than slightly unsafe. I see. So, I can't use rcu locks here as well as spinlocks. Thanks! -- Rgrds, legion