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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Andrew Lunn , netdev@vger.kernel.org Cc: Simon Horman , Dragos Tatulea , Willem de Bruijn , Matthew Schwartz References: <20260513074349.2152146-1-gal@nvidia.com> From: Gal Pressman Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: TLZP290CA0004.ISRP290.PROD.OUTLOOK.COM (2603:1096:950:9::15) To DM4PR12MB5248.namprd12.prod.outlook.com (2603:10b6:5:39c::15) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR12MB5248:EE_|SJ0PR12MB6877:EE_ X-MS-Office365-Filtering-Correlation-Id: 4b4e4af9-7cbe-4845-2f8a-08deb0e2d26d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016|7416014|56012099003|18002099003|22082099003|11063799003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM4PR12MB5248.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(376014)(366016)(7416014)(56012099003)(18002099003)(22082099003)(11063799003);DIR:OUT;SFP:1101; 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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; >>> >>> This is going to have the same checksum bug as your first commit, which >>> I'm fixing in [1]. You should use the right value of either msslen or >>> newlen when modifying check a couple of lines above. >> >> I tend to agree that the checksum seems to have the wrong value, the >> reason I chose not to change it is because my work only moved the UDP >> length assignment from the drivers to the stack. >> >> The "wrong" checksum value was used regardless of my change, > > The wrong checksum was visible only inside the driver, and since the > hardware didn't care (due to the offload), it worked well. It was the > driver business to make sure the corresponding hardware likes the > packet. After commit b10b446ce7ad ("udp: gso: Use single MSS length in > UDP header for GSO_PARTIAL"), however, the wrong checksum moved one > abstraction layer higher - to the networking stack, which attempts to > keep the checksum correct for a more generic case. It's not the same, > and while I'm trying to fix one occurrence, I'd prefer not to > introduce more. > >> and I >> prefer not to change it as part of this work. >> >>> >>> That said, maybe you can base your patch on top of my checksum fix? For >>> the last packet, it will then be: >>> >>> if (!skb_is_gso(seg)) >>> newlen = /* the new value */; >>> /* keep newlen as is otherwise: my newlen is your msslen */ >>> check = csum16_add(csum16_sub(uh->check, uh->len), newlen); >>> uh->len = newlen; >>> uh->check = check; >>> >>> [1]: https://lore.kernel.org/netdev/20260512165648.386518-3-alice.kernel@fastmail.im/ >> >> As I mentioned in the other thread, this fix goes to net, I can't take >> your patch. > > Ah, that's right. Still, I guess you can take mine to net for the > checksum fix. Do you think it is suitable for net? Would you like to rephrase the commit message accordingly? If you can send me an updated version I will take it and submit both (or you can submit mine if you prefer).