linux-kernel - Re: [PATCH net-next v9 2/9] net: add get_netmem/put

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Message-ID: <484ecaad-56de-4c0d-b7fa-a3337557b0bf@gmail.com>
Date: Tue, 22 Apr 2025 09:45:04 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 io-uring@...r.kernel.org, virtualization@...ts.linux.dev,
 kvm@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 Donald Hunter <donald.hunter@...il.com>, Jonathan Corbet <corbet@....net>,
 Andrew Lunn <andrew+netdev@...n.ch>, Jeroen de Borst <jeroendb@...gle.com>,
 Harshitha Ramamurthy <hramamurthy@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...zon.com>, Willem de Bruijn
 <willemb@...gle.com>, Jens Axboe <axboe@...nel.dk>,
 David Ahern <dsahern@...nel.org>, Neal Cardwell <ncardwell@...gle.com>,
 "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>,
 Stefano Garzarella <sgarzare@...hat.com>, Shuah Khan <shuah@...nel.org>,
 sdf@...ichev.me, dw@...idwei.uk, Jamal Hadi Salim <jhs@...atatu.com>,
 Victor Nogueira <victor@...atatu.com>, Pedro Tammela
 <pctammela@...atatu.com>, Samiullah Khawaja <skhawaja@...gle.com>
Subject: Re: [PATCH net-next v9 2/9] net: add get_netmem/put_netmem support

On 4/18/25 00:15, Mina Almasry wrote:
> Currently net_iovs support only pp ref counts, and do not support a
> page ref equivalent.

Makes me wonder why it's needed. In theory, nobody should ever be
taking page references without going through struct ubuf_info
handling first, all in kernel users of these pages should always
be paired with ubuf_info, as it's user memory, it's not stable,
and without ubuf_info the user is allowed to overwrite it.

Maybe there are some gray area cases like packet inspection or
tracing? However in this case, after the ubuf_info is dropped, the
user can overwrite the memory with its secrets. Definitely iffy
in security terms.

-- 
Pavel Begunkov