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Wed, 13 May 2026 00:43:49 -0700 From: Gal Pressman To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Andrew Lunn , CC: Simon Horman , Dragos Tatulea , Willem de Bruijn , Gal Pressman , "Matthew Schwartz" Subject: [PATCH net] udp: Fix UDP length on last GSO_PARTIAL segment Date: Wed, 13 May 2026 10:43:49 +0300 Message-ID: <20260513074349.2152146-1-gal@nvidia.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF00002314:EE_|MW6PR12MB8664:EE_ X-MS-Office365-Filtering-Correlation-Id: e425d3a1-efa0-4f0a-4c54-08deb0c36e5e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|82310400026|36860700016|13003099007|18002099003|56012099003|11063799003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.117.160;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge1.nvidia.com;CAT:NONE;SFS:(13230040)(1800799024)(376014)(82310400026)(36860700016)(13003099007)(18002099003)(56012099003)(11063799003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: qgiLbpL/BTxNs8tDHe26aZoGu8m2t/ulmEBVinDkOHF8IyFnP4ElpY062T3zNaISteInaC2XhMChjZ32ccXRzS1Fto/ikIC3yHM5FBgWkQQXX9Dkf5v0tywszKsEA3QCB4Ye7VrgvzHFKmd3xZOBc1xE/xHcudBluAyyGorILGz6B7spkWBnyAHq7XGgX4lyiXQS7QWDOSf82TVbsBrDUMjC7c8LZBtJOLgRp2XN1W+N0RugFvPhT1C1RotjMqqqcF3C0VGUmyfFUaI19mbycfDsUqky7/pYqFEjq+21S2/vqIhG+SRmHUeYAzVANilpnHumQRy9IURLtOJWuLhl7etPMF6hL2oJsjJPSWjxlv9C7DoY/YIqFvglUL1n2MZNsUk9yZxFNnoFMvqb5L/FGp4Jae7libWqV1NVvGh3vWE0IoQ1/zHWycIrxY6MXxeK X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 May 2026 07:44:14.8575 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: e425d3a1-efa0-4f0a-4c54-08deb0c36e5e X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF00002314.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW6PR12MB8664 Following the cited commit, __udp_gso_segment() writes single MSS length in the UDP header. The cited patch doesn't account for the fact that the last segment could be a GSO skb by itself. This could happen when the size of the packet is a multiple of MSS, hence the first segment is also the last one (there is no need for a remainder skb). When the post-loop segment is a GSO skb, assign the single MSS length in the UDP header. Fixes: b10b446ce7ad ("udp: gso: Use single MSS length in UDP header for GSO_PARTIAL") Reported-by: Matthew Schwartz Closes: https://lore.kernel.org/all/6c3fb15e-711d-4b8d-b152-e03d9b05293f@linux.dev/ Tested-by: Matthew Schwartz Reviewed-by: Dragos Tatulea Signed-off-by: Gal Pressman --- net/ipv4/udp_offload.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c index a0813d425b71..71df45f9488a 100644 --- a/net/ipv4/udp_offload.c +++ b/net/ipv4/udp_offload.c @@ -604,7 +604,7 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb, seg->data_len); check = csum16_add(csum16_sub(uh->check, uh->len), newlen); - uh->len = newlen; + uh->len = skb_is_gso(seg) ? msslen : newlen; uh->check = check; if (seg->ip_summed == CHECKSUM_PARTIAL) -- 2.52.0