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Message-ID: <87eeuepf09.fsf@x220.int.ebiederm.org>
Date: Fri, 28 Feb 2020 15:40:22 -0600
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Christian Brauner <christian.brauner@...ntu.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
Christian Brauner <christian.brauner@...ntu.com> writes:
> 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?
On top of the other series. Which is why it is a reply to it.
That I have pushed into linux-next earlier today.
No one seems worried enough about that patchset to comment on v2 so I am
just going with it.
>> 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?
Good catch. It isn't immediately obvious to me how that sentence
needs to be updated but it should be done.
Eric
>> -{
>> - 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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