ksmbd: handle caseless file creation

BugLink: https://bugs.launchpad.net/bugs/2089340

commit c5a709f08d40b1a082e44ffcde1aea4d2822ddd5 upstream.

Ray Zhang reported ksmbd can not create file if parent filename is
caseless.

Y:\>mkdir A
Y:\>echo 123 >a\b.txt
The system cannot find the path specified.
Y:\>echo 123 >A\b.txt

This patch convert name obtained by caseless lookup to parent name.

Cc: stable@vger.kernel.org # v5.15+
Reported-by: Ray Zhang <zhanglei002@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

fs/smb/server/vfs.c

@@ -1167,7 +1167,7 @@ static bool __caseless_lookup(struct dir_context *ctx, const char *name,
 	if (cmp < 0)
 		cmp = strncasecmp((char *)buf->private, name, namlen);
 	if (!cmp) {
-		memcpy((char *)buf->private, name, namlen);
+		memcpy((char *)buf->private, name, buf->used);
 		buf->dirent_count = 1;
 		return false;
 	}
@@ -1235,10 +1235,7 @@ int ksmbd_vfs_kern_path_locked(struct ksmbd_work *work, char *name,
 		char *filepath;
 		size_t path_len, remain_len;
 
-		filepath = kstrdup(name, GFP_KERNEL);
-		if (!filepath)
-			return -ENOMEM;
-
+		filepath = name;
 		path_len = strlen(filepath);
 		remain_len = path_len;
 
@@ -1281,10 +1278,9 @@ int ksmbd_vfs_kern_path_locked(struct ksmbd_work *work, char *name,
 		err = -EINVAL;
 out2:
 		path_put(parent_path);
-out1:
-		kfree(filepath);
 	}
 
+out1:
 	if (!err) {
 		err = mnt_want_write(parent_path->mnt);
 		if (err) {