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[89.24.57.65]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c24962bd8fasm20064466b.28.2026.08.21.14.45.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Aug 2026 14:45:42 -0700 (PDT) Message-ID: <34c64d08-0484-4f3b-b61a-ed68115d01a4@ovn.org> Date: Fri, 21 Aug 2026 23:45:41 +0200 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 v3 0/3] net: don't strip zerocopy frag markers from a forwarded skb To: Norbert Szetei , netdev@vger.kernel.org Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Aaron Conole , Eelco Chaudron , Ilya Maximets , Steffen Klassert , Kuan-Ting Chen , "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, dev@openvswitch.org, Jongmin Jang References: Content-Language: en-US From: Ilya Maximets Autocrypt: addr=i.maximets@ovn.org; keydata= xsFNBF77bOMBEADVZQ4iajIECGfH3hpQMQjhIQlyKX4hIB3OccKl5XvB/JqVPJWuZQRuqNQG /B70MP6km95KnWLZ4H1/5YOJK2l7VN7nO+tyF+I+srcKq8Ai6S3vyiP9zPCrZkYvhqChNOCF pNqdWBEmTvLZeVPmfdrjmzCLXVLi5De9HpIZQFg/Ztgj1AZENNQjYjtDdObMHuJQNJ6ubPIW cvOOn4WBr8NsP4a2OuHSTdVyAJwcDhu+WrS/Bj3KlQXIdPv3Zm5x9u/56NmCn1tSkLrEgi0i /nJNeH5QhPdYGtNzPixKgPmCKz54/LDxU61AmBvyRve+U80ukS+5vWk8zvnCGvL0ms7kx5sA tETpbKEV3d7CB3sQEym8B8gl0Ux9KzGp5lbhxxO995KWzZWWokVUcevGBKsAx4a/C0wTVOpP FbQsq6xEpTKBZwlCpxyJi3/PbZQJ95T8Uw6tlJkPmNx8CasiqNy2872gD1nN/WOP8m+cIQNu o6NOiz6VzNcowhEihE8Nkw9V+zfCxC8SzSBuYCiVX6FpgKzY/Tx+v2uO4f/8FoZj2trzXdLk BaIiyqnE0mtmTQE8jRa29qdh+s5DNArYAchJdeKuLQYnxy+9U1SMMzJoNUX5uRy6/3KrMoC/ 7zhn44x77gSoe7XVM6mr/mK+ViVB7v9JfqlZuiHDkJnS3yxKPwARAQABzSJJbHlhIE1heGlt ZXRzIDxpLm1heGltZXRzQG92bi5vcmc+wsGUBBMBCAA+AhsDBQsJCAcCBhUKCQgLAgQWAgMB Ah4BAheAFiEEh+ma1RKWrHCY821auffsd8gpv5YFAmfB9JAFCQyI7q0ACgkQuffsd8gpv5YQ og/8DXt1UOznvjdXRHVydbU6Ws+1iUrxlwnFH4WckoFgH4jAabt25yTa1Z4YX8Vz0mbRhTPX M/j1uORyObLem3of4YCd4ymh7nSu++KdKnNsZVHxMcoiic9ILPIaWYa8kTvyIDT2AEVfn9M+ vskM0yDbKa6TAHgr/0jCxbS+mvN0ZzDuR/LHTgy3e58097SWJohj0h3Dpu+XfuNiZCLCZ1/G AbBCPMw+r7baH/0evkX33RCBZwvh6tKu+rCatVGk72qRYNLCwF0YcGuNBsJiN9Aa/7ipkrA7 Xp7YvY3Y1OrKnQfdjp3mSXmknqPtwqnWzXvdfkWkZKShu0xSk+AjdFWCV3NOzQaH3CJ67NXm aPjJCIykoTOoQ7eEP6+m3WcgpRVkn9bGK9ng03MLSymTPmdINhC5pjOqBP7hLqYi89GN0MIT Ly2zD4m/8T8wPV9yo7GRk4kkwD0yN05PV2IzJECdOXSSStsf5JWObTwzhKyXJxQE+Kb67Wwa LYJgltFjpByF5GEO4Xe7iYTjwEoSSOfaR0kokUVM9pxIkZlzG1mwiytPadBt+VcmPQWcO5pi WxUI7biRYt4aLriuKeRpk94ai9+52KAk7Lz3KUWoyRwdZINqkI/aDZL6meWmcrOJWCUMW73e 4cMqK5XFnGqolhK4RQu+8IHkSXtmWui7LUeEvO/OwU0EXvts4wEQANCXyDOic0j2QKeyj/ga OD1oKl44JQfOgcyLVDZGYyEnyl6b/tV1mNb57y/YQYr33fwMS1hMj9eqY6tlMTNz+ciGZZWV YkPNHA+aFuPTzCLrapLiz829M5LctB2448bsgxFq0TPrr5KYx6AkuWzOVq/X5wYEM6djbWLc VWgJ3o0QBOI4/uB89xTf7mgcIcbwEf6yb/86Cs+jaHcUtJcLsVuzW5RVMVf9F+Sf/b98Lzrr 2/mIB7clOXZJSgtV79Alxym4H0cEZabwiXnigjjsLsp4ojhGgakgCwftLkhAnQT3oBLH/6ix 87ahawG3qlyIB8ZZKHsvTxbWte6c6xE5dmmLIDN44SajAdmjt1i7SbAwFIFjuFJGpsnfdQv1 OiIVzJ44kdRJG8kQWPPua/k+AtwJt/gjCxv5p8sKVXTNtIP/sd3EMs2xwbF8McebLE9JCDQ1 RXVHceAmPWVCq3WrFuX9dSlgf3RWTqNiWZC0a8Hn6fNDp26TzLbdo9mnxbU4I/3BbcAJZI9p 9ELaE9rw3LU8esKqRIfaZqPtrdm1C+e5gZa2gkmEzG+WEsS0MKtJyOFnuglGl1ZBxR1uFvbU VXhewCNoviXxkkPk/DanIgYB1nUtkPC+BHkJJYCyf9Kfl33s/bai34aaxkGXqpKv+CInARg3 fCikcHzYYWKaXS6HABEBAAHCwXwEGAEIACYCGwwWIQSH6ZrVEpascJjzbVq59+x3yCm/lgUC Z8H0qQUJDIjuxgAKCRC59+x3yCm/loAdD/wJCOhPp9711J18B9c4f+eNAk5vrC9Cj3RyOusH Hebb9HtSFm155Zz3xiizw70MSyOVikjbTocFAJo5VhkyuN0QJIP678SWzriwym+EG0B5P97h FSLBlRsTi4KD8f1Ll3OT03lD3o/5Qt37zFgD4mCD6OxAShPxhI3gkVHBuA0GxF01MadJEjMu jWgZoj75rCLG9sC6L4r28GEGqUFlTKjseYehLw0s3iR53LxS7HfJVHcFBX3rUcKFJBhuO6Ha /GggRvTbn3PXxR5UIgiBMjUlqxzYH4fe7pYR7z1m4nQcaFWW+JhY/BYHJyMGLfnqTn1FsIwP dbhEjYbFnJE9Vzvf+RJcRQVyLDn/TfWbETf0bLGHeF2GUPvNXYEu7oKddvnUvJK5U/BuwQXy TRFbae4Ie96QMcPBL9ZLX8M2K4XUydZBeHw+9lP1J6NJrQiX7MzexpkKNy4ukDzPrRE/ruui yWOKeCw9bCZX4a/uFw77TZMEq3upjeq21oi6NMTwvvWWMYuEKNi0340yZRrBdcDhbXkl9x/o skB2IbnvSB8iikbPng1ihCTXpA2yxioUQ96Akb+WEGopPWzlxTTK+T03G2ljOtspjZXKuywV Wu/eHyqHMyTu8UVcMRR44ki8wam0LMs+fH4dRxw5ck69AkV+JsYQVfI7tdOu7+r465LUfg== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/18/26 10:43 AM, Norbert Szetei wrote: > queue_userspace_packet() calls skb_tx_error() on the packet skb in its > error path, but it only borrows that skb: on the OVS_ACTION_ATTR_USERSPACE > action path do_execute_actions() ignores output_userspace()'s return value > and keeps forwarding the same skb through the flow's remaining actions. > skb_tx_error() completes the zerocopy uarg and clears SKBFL_ALL_ZEROCOPY, > and with it SKBFL_SHARED_FRAG. > > For a MSG_ZEROCOPY skb carrying page-cache frags, SKBFL_SHARED_FRAG is > what makes esp_input() skb_cow_data() instead of taking the in-place AEAD > path. Once it is stripped, a later local ESP delivery decrypts in place > over pages the sender still shares with the page cache. > > Patch 1 moves the skb_tx_error() into the one path that does drop the > packet, the "default" arm of ovs_dp_process_packet()'s switch(error). > > Patch 2 removes a second such strip, in skb_zerocopy(), which calls > skb_tx_error() on its source when skb_orphan_frags() fails. A copy helper > should not perform a destructive action on its source, and both callers > already report the error on their own drop path. MSG_ZEROCOPY skbs cannot > reach that one -- SKBFL_DONT_ORPHAN makes skb_orphan_frags() return early > -- but producers that do not set that flag, such as vhost-net, can. > Patch 3 is new in v2. It stops skb_tx_error() from touching skb_shinfo() > state that is shared with clones, so patch 1's new call site cannot reach > a live skb either. For a non-last OVS_ACTION_ATTR_RECIRC action > clone_execute() sends a skb_clone() into ovs_dp_process_packet() while > do_execute_actions() keeps forwarding the original, and skb_clone() does > not privatise the frags for these skbs -- skb_orphan_frags() returns early > on SKBFL_DONT_ORPHAN -- so a flow miss on the clone strips > SKBFL_SHARED_FRAG from the packet still in flight. Confirmed on a KASAN > build with a flow matching recirc_id 0 and actions RECIRC(1),OUTPUT(0): > with patches 1 and 2 applied it still reproduces the page-cache write, > with patch 3 on top it no longer does (5/5 runs). A kprobe on > skb_tx_error() shows the datapath drop path is still reached in both > cases, so the difference is the guard and not the reproducer. > > As Ilya noted, that makes patch 3 the general fix -- an skb can enter any > skb_tx_error() caller already cloned elsewhere in the stack -- while > patches 1 and 2 keep the callers from acting on an skb they do not own. > Removing skb_tx_error() altogether looks like the right long-term cleanup > and is planned as a net-next follow-up. > > v3: > - patch 3: Fixes tag corrected to 25121173f7b1 ("skb: api to report > errors for zero copy skbs"), the commit that added skb_tx_error() > (Ilya Maximets) > - Tested-by from Jongmin Jang picked up on patches 1 and 3 > - v2: https://lore.kernel.org/netdev/AD1B7BEE-C04C-4A1B-982C-8385F1908911@doyensec.com/ > > v2: > - new patch 3: skip the shared skb_shinfo() work in skb_tx_error() when > the skb is cloned, which also covers the OVS_ACTION_ATTR_RECIRC path > that patch 1 alone leaves open (suggested by Ilya Maximets) > - patches 1 and 2 unchanged, Reviewed-by from Ilya Maximets picked up > - v1: https://lore.kernel.org/netdev/8063260C-05C9-4997-B9B6-2135063C4858@doyensec.com/ > > Norbert Szetei (3): > openvswitch: only skb_tx_error() a packet we are about to drop > net: skbuff: don't skb_tx_error() the source skb in skb_zerocopy() > net: skbuff: don't touch shared zerocopy state in skb_tx_error() > > net/core/skbuff.c | 10 ++++++---- > net/openvswitch/datapath.c | 3 +-- > 2 files changed, 7 insertions(+), 6 deletions(-) > Unfortunately, this needs a rebase now that a conflicting change for skb_zerocopy() was merged: https://lore.kernel.org/all/20260814191336.187243-1-almasrymina@google.com/ Best regards, Ilya Maximets.