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([2620:10d:c092:600::1:4f63]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-496b4f30126sm213770875e9.13.2026.07.27.03.51.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Jul 2026 03:51:38 -0700 (PDT) Message-ID: <954583a4-e3b2-4a01-8ec0-bdb913faee69@gmail.com> Date: Mon, 27 Jul 2026 11:51:32 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net 1/1] net: devmem: prevent net-iov / page mixing To: Bobby Eshleman Cc: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev@vger.kernel.org, Mina Almasry References: <06f0d5ce07dd8593a69239cfa56745cb9c7d957c.1784717791.git.asml.silence@gmail.com> <5c3c34de-7b34-4122-a792-e91b48858f2f@gmail.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/24/26 20:07, Bobby Eshleman wrote: > On Wed, Jul 22, 2026 at 07:58:27PM +0100, Pavel Begunkov wrote: >> On 7/22/26 18:59, Bobby Eshleman wrote: >>> On Wed, Jul 22, 2026 at 11:58:46AM +0100, Pavel Begunkov wrote: >>>> We should either have net_iov or page backed frags in a single skb, >>>> otherwise it blows up down the stack. Don't allow mixing in >>>> zerocopy_fill_skb_from_devmem(). >>>> >>>> Fixes: bd61848900bff ("net: devmem: Implement TX path") >>>> Cc: stable@vger.kernel.org >>>> Signed-off-by: Pavel Begunkov >>>> --- >>>> net/core/datagram.c | 3 +++ >>>> 1 file changed, 3 insertions(+) >>>> >>>> diff --git a/net/core/datagram.c b/net/core/datagram.c >>>> index c285c6465923..35febc1c25fa 100644 >>>> --- a/net/core/datagram.c >>>> +++ b/net/core/datagram.c >>>> @@ -712,6 +712,9 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from, >>>> size_t virt_addr, size, off; >>>> struct net_iov *niov; >>>> + if (i && skb_frags_readable(skb)) >>>> + return -EEXIST; >>> >>> Are we trying to hit the -EEXIST handler in tcp_sendmsg_locked() so that >>> we start a new skb? If so, I think we might need to plumb this -EEXIST >>> case through skb_zerocopy_iter_stream() too? >> >> Easier to EFAULT. It'd more consistent, and I don't care how tcp takes >> it specifically. >> >> -- >> Pavel Begunkov >> > > One socket is allowed to queue non-devmem followed by devmem, and EFAULT > will break this case. I think EEXIST is right, just needs to propagate > up. Regardless of whether it's a good thing or not, mixing is already rejected, see zerocopy_fill_skb_from_iter(). Not 100% consistent though for the user as it's timing dependent. -- Pavel Begunkov