linux-kernel - [PATCH 2/3] uml: Create a private mount of proc for mconsole

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Message-ID: <87wo86qxcs.fsf_-_@x220.int.ebiederm.org>
Date:   Fri, 28 Feb 2020 14:18:43 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     <linux-kernel@...r.kernel.org>
Cc:     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: [PATCH 2/3] uml: Create a private mount of proc for mconsole


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();
+
 	if (umid_file_name("mconsole", file, sizeof(file)))
 		return -1;
 	snprintf(mconsole_socket_name, sizeof(file), "%s", file);
-- 
2.25.0