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[209.132.180.67]) by mx.google.com with ESMTP id q9si2470032otc.86.2020.02.11.14.46.07; Tue, 11 Feb 2020 14:46:19 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727761AbgBKWqB (ORCPT + 99 others); Tue, 11 Feb 2020 17:46:01 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:55440 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727640AbgBKWqA (ORCPT ); Tue, 11 Feb 2020 17:46:00 -0500 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j1eHy-00B7M0-0S; Tue, 11 Feb 2020 22:45:54 +0000 Date: Tue, 11 Feb 2020 22:45:53 +0000 From: Al Viro To: Alexey Gladkov 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: <20200211224553.GK23230@ZenIV.linux.org.uk> References: <20200210150519.538333-1-gladkov.alexey@gmail.com> <20200210150519.538333-8-gladkov.alexey@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200210150519.538333-8-gladkov.alexey@gmail.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.