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Message-ID: <20200228203915.jelui3l5xue5utpx@wittgenstein>
Date: Fri, 28 Feb 2020 21:39:15 +0100
From: Christian Brauner <christian.brauner@...ntu.com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux API <linux-api@...r.kernel.org>,
Linux FS Devel <linux-fsdevel@...r.kernel.org>,
Linux Security Module <linux-security-module@...r.kernel.org>,
Akinobu Mita <akinobu.mita@...il.com>,
Alexey Dobriyan <adobriyan@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>,
Daniel Micay <danielmicay@...il.com>,
Djalal Harouni <tixxdz@...il.com>,
"Dmitry V . Levin" <ldv@...linux.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Ingo Molnar <mingo@...nel.org>,
"J . Bruce Fields" <bfields@...ldses.org>,
Jeff Layton <jlayton@...chiereds.net>,
Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>,
Oleg Nesterov <oleg@...hat.com>,
Alexey Gladkov <gladkov.alexey@...il.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Jeff Dike <jdike@...toit.com>, Richard Weinberger <richard@....at>,
Anton Ivanov <anton.ivanov@...bridgegreys.com>
Subject: Re: [PATCH 3/3] proc: Remove the now unnecessary internal mount of
proc
On Fri, Feb 28, 2020 at 02:19:22PM -0600, Eric W. Biederman wrote:
>
> There remains no more code in the kernel using pids_ns->proc_mnt,
> therefore remove it from the kernel.
>
> The big benefit of this change is that one of the most error prone and
> tricky parts of the pid namespace implementation, maintaining kernel
> mounts of proc is removed.
>
> In addition removing the unnecessary complexity of the kernel mount
> fixes a regression that caused the proc mount options to be ignored.
> Now that the initial mount of proc comes from userspace, those mount
> options are again honored. This fixes Android's usage of the proc
> hidepid option.
>
> Reported-by: Alistair Strachan <astrachan@...gle.com>
> Fixes: e94591d0d90c ("proc: Convert proc_mount to use mount_ns.")
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
> fs/proc/root.c | 36 -----------------------------------
What about proc_flush_task()? Or is this on top of your other series?
> include/linux/pid_namespace.h | 2 --
> include/linux/proc_ns.h | 5 -----
> kernel/pid.c | 8 --------
> kernel/pid_namespace.c | 7 -------
> 5 files changed, 58 deletions(-)
>
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index 608233dfd29c..2633f10446c3 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -292,39 +292,3 @@ struct proc_dir_entry proc_root = {
> .subdir = RB_ROOT,
> .name = "/proc",
> };
> -
> -int pid_ns_prepare_proc(struct pid_namespace *ns)
> -{
> - struct proc_fs_context *ctx;
> - struct fs_context *fc;
> - struct vfsmount *mnt;
> -
> - fc = fs_context_for_mount(&proc_fs_type, SB_KERNMOUNT);
> - if (IS_ERR(fc))
> - return PTR_ERR(fc);
> -
> - if (fc->user_ns != ns->user_ns) {
> - put_user_ns(fc->user_ns);
> - fc->user_ns = get_user_ns(ns->user_ns);
> - }
> -
> - ctx = fc->fs_private;
> - if (ctx->pid_ns != ns) {
> - put_pid_ns(ctx->pid_ns);
> - get_pid_ns(ns);
> - ctx->pid_ns = ns;
> - }
> -
> - mnt = fc_mount(fc);
> - put_fs_context(fc);
> - if (IS_ERR(mnt))
> - return PTR_ERR(mnt);
> -
> - ns->proc_mnt = mnt;
> - return 0;
> -}
> -
> -void pid_ns_release_proc(struct pid_namespace *ns)
> -{
> - kern_unmount(ns->proc_mnt);
> -}
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index 2ed6af88794b..4956e362e55e 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -33,7 +33,6 @@ struct pid_namespace {
> unsigned int level;
> struct pid_namespace *parent;
> #ifdef CONFIG_PROC_FS
> - struct vfsmount *proc_mnt;
> struct dentry *proc_self;
> struct dentry *proc_thread_self;
> #endif
> @@ -42,7 +41,6 @@ struct pid_namespace {
> #endif
> struct user_namespace *user_ns;
> struct ucounts *ucounts;
> - struct work_struct proc_work;
> kgid_t pid_gid;
> int hide_pid;
> int reboot; /* group exit code if this pidns was rebooted */
> diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
> index 4626b1ac3b6c..e1106a077c1a 100644
> --- a/include/linux/proc_ns.h
> +++ b/include/linux/proc_ns.h
> @@ -50,16 +50,11 @@ enum {
>
> #ifdef CONFIG_PROC_FS
>
> -extern int pid_ns_prepare_proc(struct pid_namespace *ns);
> -extern void pid_ns_release_proc(struct pid_namespace *ns);
> extern int proc_alloc_inum(unsigned int *pino);
> extern void proc_free_inum(unsigned int inum);
>
> #else /* CONFIG_PROC_FS */
>
> -static inline int pid_ns_prepare_proc(struct pid_namespace *ns) { return 0; }
> -static inline void pid_ns_release_proc(struct pid_namespace *ns) {}
> -
> static inline int proc_alloc_inum(unsigned int *inum)
> {
> *inum = 1;
> diff --git a/kernel/pid.c b/kernel/pid.c
> index ca08d6a3aa77..60820e72634c 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -144,9 +144,6 @@ void free_pid(struct pid *pid)
> /* Handle a fork failure of the first process */
> WARN_ON(ns->child_reaper);
> ns->pid_allocated = 0;
> - /* fall through */
> - case 0:
> - schedule_work(&ns->proc_work);
> break;
> }
>
> @@ -247,11 +244,6 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
> tmp = tmp->parent;
> }
>
> - if (unlikely(is_child_reaper(pid))) {
> - if (pid_ns_prepare_proc(ns))
> - goto out_free;
> - }
> -
> get_pid_ns(ns);
> refcount_set(&pid->count, 1);
> for (type = 0; type < PIDTYPE_MAX; ++type)
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index d40017e79ebe..318fcc6ba301 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -57,12 +57,6 @@ static struct kmem_cache *create_pid_cachep(unsigned int level)
> return READ_ONCE(*pkc);
> }
>
> -static void proc_cleanup_work(struct work_struct *work)
There's a comment in kernel/pid_namespace.c that references
proc_cleanup_work(). Can you please remove that as well?
> -{
> - struct pid_namespace *ns = container_of(work, struct pid_namespace, proc_work);
> - pid_ns_release_proc(ns);
> -}
> -
> static struct ucounts *inc_pid_namespaces(struct user_namespace *ns)
> {
> return inc_ucount(ns, current_euid(), UCOUNT_PID_NAMESPACES);
> @@ -114,7 +108,6 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
> ns->user_ns = get_user_ns(user_ns);
> ns->ucounts = ucounts;
> ns->pid_allocated = PIDNS_ADDING;
> - INIT_WORK(&ns->proc_work, proc_cleanup_work);
>
> return ns;
>
> --
> 2.25.0
>
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