ksmbd: fix use-after-free in kerberos authentication

Setting sess->user = NULL was introduced to fix the dangling pointer
created by ksmbd_free_user. However, it is possible another thread could
be operating on the session and make use of sess->user after it has been
passed to ksmbd_free_user but before sess->user is set to NULL.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Heelan <seanheelan@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/server/auth.c b/fs/smb/server/auth.c
index 83caa38497493251aa72c94d25309585dd7314ad..b3d121052408cca062ce72f570e8bff690a0a283 100644 (file)
--- a/fs/smb/server/auth.c
+++ b/fs/smb/server/auth.c
@@ -550,7 +550,19 @@ int ksmbd_krb5_authenticate(struct ksmbd_session *sess, char *in_blob,
                retval = -ENOMEM;
                goto out;
        }
-       sess->user = user;
+
+       if (!sess->user) {
+               /* First successful authentication */
+               sess->user = user;
+       } else {
+               if (!ksmbd_compare_user(sess->user, user)) {
+                       ksmbd_debug(AUTH, "different user tried to reuse session\n");
+                       retval = -EPERM;
+                       ksmbd_free_user(user);
+                       goto out;
+               }
+               ksmbd_free_user(user);
+       }
 
        memcpy(sess->sess_key, resp->payload, resp->session_key_len);
        memcpy(out_blob, resp->payload + resp->session_key_len,

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 372021b3f2632cd30aea3500c6de6553c66047de..acc05657cfc72ad38160bad711c8499997c38632 100644 (file)
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -1607,11 +1607,6 @@ static int krb5_authenticate(struct ksmbd_work *work,
        if (prev_sess_id && prev_sess_id != sess->id)
                destroy_previous_session(conn, sess->user, prev_sess_id);
 
-       if (sess->state == SMB2_SESSION_VALID) {
-               ksmbd_free_user(sess->user);
-               sess->user = NULL;
-       }
-
        retval = ksmbd_krb5_authenticate(sess, in_blob, in_len,
                                         out_blob, &out_len);
        if (retval) {