ksmbd: Fix dangling pointer in krb_authenticate

commit 1e440d5b25b7efccb3defe542a73c51005799a5f upstream.

krb_authenticate frees sess->user and does not set the pointer
to NULL. It calls ksmbd_krb5_authenticate to reinitialise
sess->user but that function may return without doing so. If
that happens then smb2_sess_setup, which calls krb_authenticate,
will be accessing free'd memory when it later uses sess->user.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index dbe272970c25b8961386f0fa71f4c10b369ccccc..c0e159592655a0050c15df0e10bb76ec8628e262 100644 (file)
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -1615,8 +1615,10 @@ 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)
+       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);