ksmbd: fix translation in create_posix_rsp_buf()

When transferring ownership information to the client the k*ids are
translated into raw *ids before they are sent over the wire. The
function currently erroneously translates the k*ids according to the
mount's idmapping. Instead, reporting the owning *ids to userspace the
underlying k*ids need to be mapped up in the caller's user namespace.
This is how stat() works.
The caller in this instance is ksmbd itself and ksmbd always runs in the
initial user namespace. Translate according to that taking any potential
idmapped mounts into account.

Switch to from_k*id_munged() which ensures that the overflow*id is
returned instead of the (*id_t)-1 when the k*id can't be translated.

Cc: Steve French <stfrench@microsoft.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Namjae Jeon <namjae.jeon@samsung.com>
Cc: Hyunchul Lee <hyc.lee@gmail.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/oplock.c

@@ -1614,9 +1614,11 @@ void create_posix_rsp_buf(char *cc, struct ksmbd_file *fp)
 	buf->nlink = cpu_to_le32(inode->i_nlink);
 	buf->reparse_tag = cpu_to_le32(fp->volatile_id);
 	buf->mode = cpu_to_le32(inode->i_mode);
-	id_to_sid(from_kuid(user_ns, inode->i_uid),
+	id_to_sid(from_kuid_munged(&init_user_ns,
+				   i_uid_into_mnt(user_ns, inode)),
 		  SIDNFS_USER, (struct smb_sid *)&buf->SidBuffer[0]);
-	id_to_sid(from_kgid(user_ns, inode->i_gid),
+	id_to_sid(from_kgid_munged(&init_user_ns,
+				   i_gid_into_mnt(user_ns, inode)),
 		  SIDNFS_GROUP, (struct smb_sid *)&buf->SidBuffer[20]);
 }