linux-kernel - [PATCH v5 1/3] init/main.c: introduce function ramdisk_exec

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Message-Id: <20210604120727.58410-2-dong.menglong@zte.com.cn>
Date:   Fri,  4 Jun 2021 05:07:25 -0700
From:   menglong8.dong@...il.com
To:     christian.brauner@...ntu.com
Cc:     viro@...iv.linux.org.uk, keescook@...omium.org,
        samitolvanen@...gle.com, ojeda@...nel.org, johan@...nel.org,
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Subject: [PATCH v5 1/3] init/main.c: introduce function ramdisk_exec_exist()

From: Menglong Dong <dong.menglong@....com.cn>

Introduce the function ramdisk_exec_exist, which is used to check the
exist of 'ramdisk_execute_command'.

To make path lookup follow the mount on '/', use vfs_path_lookup() in
init_eaccess(), and make the filesystem that mounted on '/' as root
during path lookup.

Signed-off-by: Menglong Dong <dong.menglong@....com.cn>
---
 fs/init.c            | 11 +++++++++--
 include/linux/init.h |  1 +
 init/main.c          |  7 ++++++-
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/fs/init.c b/fs/init.c
index 5c36adaa9b44..166356a1f15f 100644
--- a/fs/init.c
+++ b/fs/init.c
@@ -112,14 +112,21 @@ int __init init_chmod(const char *filename, umode_t mode)
 
 int __init init_eaccess(const char *filename)
 {
-	struct path path;
+	struct path path, root;
 	int error;
 
-	error = kern_path(filename, LOOKUP_FOLLOW, &path);
+	error = kern_path("/", LOOKUP_DOWN, &root);
 	if (error)
 		return error;
+	error = vfs_path_lookup(root.dentry, root.mnt, filename,
+				LOOKUP_FOLLOW, &path);
+	if (error)
+		goto on_err;
 	error = path_permission(&path, MAY_ACCESS);
+
 	path_put(&path);
+on_err:
+	path_put(&root);
 	return error;
 }
 
diff --git a/include/linux/init.h b/include/linux/init.h
index d82b4b2e1d25..889d538b6dfa 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -149,6 +149,7 @@ extern unsigned int reset_devices;
 void setup_arch(char **);
 void prepare_namespace(void);
 void __init init_rootfs(void);
+bool ramdisk_exec_exist(void);
 extern struct file_system_type rootfs_fs_type;
 
 #if defined(CONFIG_STRICT_KERNEL_RWX) || defined(CONFIG_STRICT_MODULE_RWX)
diff --git a/init/main.c b/init/main.c
index eb01e121d2f1..1153571ca977 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1522,6 +1522,11 @@ void __init console_on_rootfs(void)
 	fput(file);
 }
 
+bool __init ramdisk_exec_exist(void)
+{
+	return init_eaccess(ramdisk_execute_command) == 0;
+}
+
 static noinline void __init kernel_init_freeable(void)
 {
 	/*
@@ -1568,7 +1573,7 @@ static noinline void __init kernel_init_freeable(void)
 	 * check if there is an early userspace init.  If yes, let it do all
 	 * the work
 	 */
-	if (init_eaccess(ramdisk_execute_command) != 0) {
+	if (!ramdisk_exec_exist()) {
 		ramdisk_execute_command = NULL;
 		prepare_namespace();
 	}
-- 
2.32.0.rc0