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Message-ID: <20200228215920.tlw74xzhl5qkvt4p@wittgenstein>
Date: Fri, 28 Feb 2020 22:59:20 +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 2/3] uml: Create a private mount of proc for mconsole
On Fri, Feb 28, 2020 at 03:28:54PM -0600, Eric W. Biederman wrote:
> Christian Brauner <christian.brauner@...ntu.com> writes:
>
> > On Fri, Feb 28, 2020 at 02:18:43PM -0600, Eric W. Biederman wrote:
> >>
> >> The mconsole code only ever accesses proc for the initial pid
> >> namespace. Instead of depending upon the proc_mnt which is
> >> for proc_flush_task have uml create it's own mount of proc
> >> instead.
> >>
> >> This allows proc_flush_task to evolve and remove the
> >> need for having a proc_mnt to do it's job.
> >>
> >> Cc: Jeff Dike <jdike@...toit.com>
> >> Cc: Richard Weinberger <richard@....at>
> >> Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
> >> Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
> >> ---
> >> arch/um/drivers/mconsole_kern.c | 28 +++++++++++++++++++++++++++-
> >> 1 file changed, 27 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
> >> index e8f5c81c2c6c..30575bd92975 100644
> >> --- a/arch/um/drivers/mconsole_kern.c
> >> +++ b/arch/um/drivers/mconsole_kern.c
> >> @@ -36,6 +36,8 @@
> >> #include "mconsole_kern.h"
> >> #include <os.h>
> >>
> >> +static struct vfsmount *proc_mnt = NULL;
> >> +
> >> static int do_unlink_socket(struct notifier_block *notifier,
> >> unsigned long what, void *data)
> >> {
> >> @@ -123,7 +125,7 @@ void mconsole_log(struct mc_request *req)
> >>
> >> void mconsole_proc(struct mc_request *req)
> >> {
> >> - struct vfsmount *mnt = init_pid_ns.proc_mnt;
> >> + struct vfsmount *mnt = proc_mnt;
> >> char *buf;
> >> int len;
> >> struct file *file;
> >> @@ -134,6 +136,10 @@ void mconsole_proc(struct mc_request *req)
> >> ptr += strlen("proc");
> >> ptr = skip_spaces(ptr);
> >>
> >> + if (!mnt) {
> >> + mconsole_reply(req, "Proc not available", 1, 0);
> >> + goto out;
> >> + }
> >> file = file_open_root(mnt->mnt_root, mnt, ptr, O_RDONLY, 0);
> >> if (IS_ERR(file)) {
> >> mconsole_reply(req, "Failed to open file", 1, 0);
> >> @@ -683,6 +689,24 @@ void mconsole_stack(struct mc_request *req)
> >> with_console(req, stack_proc, to);
> >> }
> >>
> >> +static int __init mount_proc(void)
> >> +{
> >> + struct file_system_type *proc_fs_type;
> >> + struct vfsmount *mnt;
> >> +
> >> + proc_fs_type = get_fs_type("proc");
> >> + if (!proc_fs_type)
> >> + return -ENODEV;
> >> +
> >> + mnt = kern_mount(proc_fs_type);
> >> + put_filesystem(proc_fs_type);
> >> + if (IS_ERR(mnt))
> >> + return PTR_ERR(mnt);
> >> +
> >> + proc_mnt = mnt;
> >> + return 0;
> >> +}
> >> +
> >> /*
> >> * Changed by mconsole_setup, which is __setup, and called before SMP is
> >> * active.
> >> @@ -696,6 +720,8 @@ static int __init mconsole_init(void)
> >> int err;
> >> char file[UNIX_PATH_MAX];
> >>
> >> + mount_proc();
> >
> > Hm, either check the return value or make the mount_proc() void?
> > Probably worth logging something but moving on without proc.
>
> I modified mconsole_proc (the only place that cares to see if
> it has a valid proc_mnt).
>
> So the code already does the moving on without mounting proc
> and continues to work.
Ok, but then make mount_proc()
static void __init mount_proc(void)
and not
static int __init mount_proc(void)
like you have now. That was what I was getting it. Unless there's
another reason for this.
Christian
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