ksmbd: use scoped_with_init_fs() for VFS path operations

Use scoped_with_init_fs() to temporarily override current->fs for
path lookups in ksmbd VFS helpers:
- ksmbd_vfs_path_lookup(): wrap vfs_path_parent_lookup()
- ksmbd_vfs_link(): wrap kern_path() for old path resolution
- ksmbd_vfs_kern_path_create(): wrap start_creating_path()

This ensures path lookups happen in init's filesystem context.

All ksmbd paths ← SMB command handlers ← handle_ksmbd_work() ← workqueue
← ksmbd_conn_handler_loop() ← kthread

Link: https://patch.msgid.link/20260601-work-kthread-nullfs-v4-15-77ee053060e0@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index f5fa22d87603..d6dba827307d 100644
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -7,6 +7,7 @@
 #include <crypto/sha2.h>
 #include <linux/kernel.h>
 #include <linux/fs.h>
+#include <linux/fs_struct.h>
 #include <linux/filelock.h>
 #include <linux/uaccess.h>
 #include <linux/backing-dev.h>
@@ -67,8 +68,9 @@ static int ksmbd_vfs_path_lookup(struct ksmbd_share_config *share_conf,
 	}
 
 	CLASS(filename_kernel, filename)(pathname);
-	err = vfs_path_parent_lookup(filename, flags, path, &last,
-				     root_share_path);
+	scoped_with_init_fs()
+		err = vfs_path_parent_lookup(filename, flags, path, &last,
+					     root_share_path);
 	if (err)
 		return err;
 
@@ -623,7 +625,8 @@ int ksmbd_vfs_link(struct ksmbd_work *work, const char *oldname,
 	if (ksmbd_override_fsids(work))
 		return -ENOMEM;
 
-	err = kern_path(oldname, LOOKUP_NO_SYMLINKS, &oldpath);
+	scoped_with_init_fs()
+		err = kern_path(oldname, LOOKUP_NO_SYMLINKS, &oldpath);
 	if (err) {
 		pr_err("cannot get linux path for %s, err = %d\n",
 		       oldname, err);