ksmbd: fix racy issue from using ->d_parent and ->d_name

Al pointed out that ksmbd has racy issue from using ->d_parent and ->d_name
in ksmbd_vfs_unlink and smb2_vfs_rename(). and use new lock_rename_child()
to lock stable parent while underlying rename racy.
Introduce vfs_path_parent_lookup helper to avoid out of share access and
export vfs functions like the following ones to use
vfs_path_parent_lookup().
 - rename __lookup_hash() to lookup_one_qstr_excl().
 - export lookup_one_qstr_excl().
 - export getname_kernel() and putname().

vfs_path_parent_lookup() is used for parent lookup of destination file
using absolute pathname given from FILE_RENAME_INFORMATION request.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/namei.h b/include/linux/namei.h
index 5864e4d82e56..1463cbda4888 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -57,12 +57,18 @@ static inline int user_path_at(int dfd, const char __user *name, unsigned flags,
 	return user_path_at_empty(dfd, name, flags, path, NULL);
 }
 
+struct dentry *lookup_one_qstr_excl(const struct qstr *name,
+				    struct dentry *base,
+				    unsigned int flags);
 extern int kern_path(const char *, unsigned, struct path *);
 
 extern struct dentry *kern_path_create(int, const char *, struct path *, unsigned int);
 extern struct dentry *user_path_create(int, const char __user *, struct path *, unsigned int);
 extern void done_path_create(struct path *, struct dentry *);
 extern struct dentry *kern_path_locked(const char *, struct path *);
+int vfs_path_parent_lookup(struct filename *filename, unsigned int flags,
+			   struct path *parent, struct qstr *last, int *type,
+			   const struct path *root);
 int vfs_path_lookup(struct dentry *, struct vfsmount *, const char *,
 		    unsigned int, struct path *);