linux-kernel - [PATCH v7 1/2] init/main.c: introduce function ramdisk_exec

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Date:   Mon, 17 Jan 2022 13:43:51 +0000
From:   cgel.zte@...il.com
To:     mhiramat@...nel.org
Cc:     viro@...iv.linux.org.uk, keescook@...omium.org,
        samitolvanen@...gle.com, ojeda@...nel.org, johan@...nel.org,
        bhelgaas@...gle.com, elver@...gle.com, masahiroy@...nel.org,
        zhang.yunkai@....com.cn, axboe@...nel.dk, vgoyal@...hat.com,
        jack@...e.cz, leon@...nel.org, akpm@...ux-foundation.org,
        rppt@...nel.org, linux@...musvillemoes.dk,
        palmerdabbelt@...gle.com, f.fainelli@...il.com,
        wangkefeng.wang@...wei.com, rostedt@...dmis.org,
        ahalaney@...hat.com, valentin.schneider@....com,
        peterz@...radead.org, geert@...ux-m68k.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Menglong Dong <dong.menglong@....com.cn>
Subject: [PATCH v7 1/2] init/main.c: introduce function ramdisk_exec_exist()

From: Zhang Yunkai <zhang.yunkai@....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.

Reported-by: Menglong Dong <dong.menglong@....com.cn>
Signed-off-by: Zhang Yunkai <zhang.yunkai@....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 bb984ed79de0..ed1c63f4ed87 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1577,6 +1577,11 @@ 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)
 {
 	/* Now the scheduler is fully set up and can do blocking allocations */
@@ -1618,7 +1623,7 @@ 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();
 	}
-- 
2.25.1