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Message-ID: <20200228203058.jcnqeyvmqhfslcym@wittgenstein>
Date: Fri, 28 Feb 2020 21:30:58 +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 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 guess this is user visible in some scenarios but the patch series
seems worth it!
Christian
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