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

[ Upstream commit 74d7970 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/namei.c

@@ -253,6 +253,7 @@ getname_kernel(const char * filename)
 
 	return result;
 }
+EXPORT_SYMBOL(getname_kernel);
 
 void putname(struct filename *name)
 {
@@ -271,6 +272,7 @@ void putname(struct filename *name)
 	} else
 		__putname(name);
 }
+EXPORT_SYMBOL(putname);
 
 /**
  * check_acl - perform ACL permission checking
@@ -1581,8 +1583,9 @@ static struct dentry *lookup_dcache(const struct qstr *name,
  * when directory is guaranteed to have no in-lookup children
  * at all.
  */
-static struct dentry *__lookup_hash(const struct qstr *name,
-		struct dentry *base, unsigned int flags)
+struct dentry *lookup_one_qstr_excl(const struct qstr *name,
+				    struct dentry *base,
+				    unsigned int flags)
 {
 	struct dentry *dentry = lookup_dcache(name, base, flags);
 	struct dentry *old;
@@ -1606,6 +1609,7 @@ static struct dentry *__lookup_hash(const struct qstr *name,
 	}
 	return dentry;
 }
+EXPORT_SYMBOL(lookup_one_qstr_excl);
 
 static struct dentry *lookup_fast(struct nameidata *nd)
 {
@@ -2532,16 +2536,17 @@ static int path_parentat(struct nameidata *nd, unsigned flags,
 }
 
 /* Note: this does not consume "name" */
-static int filename_parentat(int dfd, struct filename *name,
-			     unsigned int flags, struct path *parent,
-			     struct qstr *last, int *type)
+static int __filename_parentat(int dfd, struct filename *name,
+			       unsigned int flags, struct path *parent,
+			       struct qstr *last, int *type,
+			       const struct path *root)
 {
 	int retval;
 	struct nameidata nd;
 
 	if (IS_ERR(name))
 		return PTR_ERR(name);
-	set_nameidata(&nd, dfd, name, NULL);
+	set_nameidata(&nd, dfd, name, root);
 	retval = path_parentat(&nd, flags | LOOKUP_RCU, parent);
 	if (unlikely(retval == -ECHILD))
 		retval = path_parentat(&nd, flags, parent);
@@ -2556,6 +2561,13 @@ static int filename_parentat(int dfd, struct filename *name,
 	return retval;
 }
 
+static int filename_parentat(int dfd, struct filename *name,
+			     unsigned int flags, struct path *parent,
+			     struct qstr *last, int *type)
+{
+	return __filename_parentat(dfd, name, flags, parent, last, type, NULL);
+}
+
 /* does lookup, returns the object with parent locked */
 static struct dentry *__kern_path_locked(struct filename *name, struct path *path)
 {
@@ -2571,7 +2583,7 @@ static struct dentry *__kern_path_locked(struct filename *name, struct path *pat
 		return ERR_PTR(-EINVAL);
 	}
 	inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
-	d = __lookup_hash(&last, path->dentry, 0);
+	d = lookup_one_qstr_excl(&last, path->dentry, 0);
 	if (IS_ERR(d)) {
 		inode_unlock(path->dentry->d_inode);
 		path_put(path);
@@ -2599,6 +2611,24 @@ int kern_path(const char *name, unsigned int flags, struct path *path)
 }
 EXPORT_SYMBOL(kern_path);
 
+/**
+ * vfs_path_parent_lookup - lookup a parent path relative to a dentry-vfsmount pair
+ * @filename: filename structure
+ * @flags: lookup flags
+ * @parent: pointer to struct path to fill
+ * @last: last component
+ * @type: type of the last component
+ * @root: pointer to struct path of the base directory
+ */
+int vfs_path_parent_lookup(struct filename *filename, unsigned int flags,
+			   struct path *parent, struct qstr *last, int *type,
+			   const struct path *root)
+{
+	return  __filename_parentat(AT_FDCWD, filename, flags, parent, last,
+				    type, root);
+}
+EXPORT_SYMBOL(vfs_path_parent_lookup);
+
 /**
  * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair
  * @dentry:  pointer to dentry of the base directory
@@ -3852,7 +3882,8 @@ static struct dentry *filename_create(int dfd, struct filename *name,
 	if (last.name[last.len] && !want_dir)
 		create_flags = 0;
 	inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT);
-	dentry = __lookup_hash(&last, path->dentry, reval_flag | create_flags);
+	dentry = lookup_one_qstr_excl(&last, path->dentry,
+				      reval_flag | create_flags);
 	if (IS_ERR(dentry))
 		goto unlock;
 
@@ -4214,7 +4245,7 @@ int do_rmdir(int dfd, struct filename *name)
 		goto exit2;
 
 	inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT);
-	dentry = __lookup_hash(&last, path.dentry, lookup_flags);
+	dentry = lookup_one_qstr_excl(&last, path.dentry, lookup_flags);
 	error = PTR_ERR(dentry);
 	if (IS_ERR(dentry))
 		goto exit3;
@@ -4348,7 +4379,7 @@ int do_unlinkat(int dfd, struct filename *name)
 		goto exit2;
 retry_deleg:
 	inode_lock_nested(path.dentry->d_inode, I_MUTEX_PARENT);
-	dentry = __lookup_hash(&last, path.dentry, lookup_flags);
+	dentry = lookup_one_qstr_excl(&last, path.dentry, lookup_flags);
 	error = PTR_ERR(dentry);
 	if (!IS_ERR(dentry)) {
 		struct user_namespace *mnt_userns;
@@ -4922,15 +4953,17 @@ int do_renameat2(int olddfd, struct filename *from, int newdfd,
 retry_deleg:
 	trap = lock_rename(new_path.dentry, old_path.dentry);
 
-	old_dentry = __lookup_hash(&old_last, old_path.dentry, lookup_flags);
+	old_dentry = lookup_one_qstr_excl(&old_last, old_path.dentry,
+					  lookup_flags);
 	error = PTR_ERR(old_dentry);
 	if (IS_ERR(old_dentry))
 		goto exit3;
 	/* source must exist */
 	error = -ENOENT;
 	if (d_is_negative(old_dentry))
 		goto exit4;
-	new_dentry = __lookup_hash(&new_last, new_path.dentry, lookup_flags | target_flags);
+	new_dentry = lookup_one_qstr_excl(&new_last, new_path.dentry,
+					  lookup_flags | target_flags);
 	error = PTR_ERR(new_dentry);
 	if (IS_ERR(new_dentry))
 		goto exit4;