netdev - Re: [RFC 0/1] whitelisting UDP GSO and GRO cmsgs

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Date:   Mon, 30 Nov 2020 16:05:35 +0100
From:   Stefan Metzmacher <metze@...ba.org>
To:     Soheil Hassas Yeganeh <soheil@...gle.com>
Cc:     Victor Stewart <v@...etag.social>,
        io-uring <io-uring@...r.kernel.org>,
        Luke Hsiao <lukehsiao@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jann Horn <jannh@...gle.com>, Arjun Roy <arjunroy@...gle.com>,
        netdev <netdev@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [RFC 0/1] whitelisting UDP GSO and GRO cmsgs

Hi Soheil,

> Thank you for CCing us.
> 
> The reason for PROTO_CMSG_DATA_ONLY is explained in the paragraph
> above in the commit message.  PROTO_CMSG_DATA_ONLY is basically to
> allow-list a protocol that is guaranteed not to have the privilege
> escalation in https://crbug.com/project-zero/1975.  TCP doesn't have
> that issue, and I believe UDP doesn't have that issue either (but
> please audit and confirm that with +Jann Horn).
> 
> If you couldn't find any non-data CMSGs for UDP, you should just add
> PROTO_CMSG_DATA_ONLY to inet dgram sockets instead of introducing
> __sys_whitelisted_cmsghdrs as Stefan mentioned.

Was there a specific reason why you only added the PROTO_CMSG_DATA_ONLY check
in __sys_recvmsg_sock(), but not in __sys_sendmsg_sock()?

metze





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