[PATCH v4 27/40] init: handle idmapped mounts

[Christian Brauner <christian.brauner@xxxxxxxxxx>]

Enable the init helpers to handle idmapped mounts by passing down the
mount's user namespace. If the initial user namespace is passed nothing
changes so non-idmapped mounts will see identical behavior as before.

Cc: Christoph Hellwig <hch@xxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
---
/* v2 */
patch introduced

/* v3 */
unchanged

/* v4 */
unchanged
---
 fs/init.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/fs/init.c b/fs/init.c
index 06d8e52ce18e..1db2b392e4e6 100644
--- a/fs/init.c
+++ b/fs/init.c
@@ -49,7 +49,7 @@ int __init init_chdir(const char *filename)
 	error = kern_path(filename, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
 	if (error)
 		return error;
-	error = inode_permission(&init_user_ns, path.dentry->d_inode,
+	error = inode_permission(mnt_user_ns(path.mnt), path.dentry->d_inode,
 				 MAY_EXEC | MAY_CHDIR);
 	if (!error)
 		set_fs_pwd(current->fs, &path);
@@ -65,7 +65,7 @@ int __init init_chroot(const char *filename)
 	error = kern_path(filename, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path);
 	if (error)
 		return error;
-	error = inode_permission(&init_user_ns, path.dentry->d_inode,
+	error = inode_permission(mnt_user_ns(path.mnt), path.dentry->d_inode,
 				 MAY_EXEC | MAY_CHDIR);
 	if (error)
 		goto dput_and_out;
@@ -120,7 +120,7 @@ int __init init_eaccess(const char *filename)
 	error = kern_path(filename, LOOKUP_FOLLOW, &path);
 	if (error)
 		return error;
-	error = inode_permission(&init_user_ns, d_inode(path.dentry),
+	error = inode_permission(mnt_user_ns(path.mnt), d_inode(path.dentry),
 				 MAY_ACCESS);
 	path_put(&path);
 	return error;
@@ -160,8 +160,8 @@ int __init init_mknod(const char *filename, umode_t mode, unsigned int dev)
 		mode &= ~current_umask();
 	error = security_path_mknod(&path, dentry, mode, dev);
 	if (!error)
-		error = vfs_mknod(&init_user_ns, path.dentry->d_inode, dentry,
-				  mode, new_decode_dev(dev));
+		error = vfs_mknod(mnt_user_ns(path.mnt), path.dentry->d_inode,
+				  dentry, mode, new_decode_dev(dev));
 	done_path_create(&path, dentry);
 	return error;
 }
@@ -170,6 +170,7 @@ int __init init_link(const char *oldname, const char *newname)
 {
 	struct dentry *new_dentry;
 	struct path old_path, new_path;
+	struct user_namespace *mnt_userns;
 	int error;
 
 	error = kern_path(oldname, 0, &old_path);
@@ -184,14 +185,15 @@ int __init init_link(const char *oldname, const char *newname)
 	error = -EXDEV;
 	if (old_path.mnt != new_path.mnt)
 		goto out_dput;
-	error = may_linkat(&init_user_ns, &old_path);
+	mnt_userns = mnt_user_ns(new_path.mnt);
+	error = may_linkat(mnt_userns, &old_path);
 	if (unlikely(error))
 		goto out_dput;
 	error = security_path_link(old_path.dentry, &new_path, new_dentry);
 	if (error)
 		goto out_dput;
-	error = vfs_link(old_path.dentry, &init_user_ns,
-			 new_path.dentry->d_inode, new_dentry, NULL);
+	error = vfs_link(old_path.dentry, mnt_userns, new_path.dentry->d_inode,
+			 new_dentry, NULL);
 out_dput:
 	done_path_create(&new_path, new_dentry);
 out:
@@ -210,7 +212,8 @@ int __init init_symlink(const char *oldname, const char *newname)
 		return PTR_ERR(dentry);
 	error = security_path_symlink(&path, dentry, oldname);
 	if (!error)
-		error = vfs_symlink(&init_user_ns, path.dentry->d_inode, dentry, oldname);
+		error = vfs_symlink(mnt_user_ns(path.mnt), path.dentry->d_inode,
+				    dentry, oldname);
 	done_path_create(&path, dentry);
 	return error;
 }
@@ -233,7 +236,8 @@ int __init init_mkdir(const char *pathname, umode_t mode)
 		mode &= ~current_umask();
 	error = security_path_mkdir(&path, dentry, mode);
 	if (!error)
-		error = vfs_mkdir(&init_user_ns, path.dentry->d_inode, dentry, mode);
+		error = vfs_mkdir(mnt_user_ns(path.mnt), path.dentry->d_inode,
+				  dentry, mode);
 	done_path_create(&path, dentry);
 	return error;
 }
-- 
2.29.2