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[195.231.44.239]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49954221f32sm83719565e9.9.2026.08.06.09.28.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Aug 2026 09:28:02 -0700 (PDT) Message-ID: Date: Thu, 6 Aug 2026 18:28:00 +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 1/1] ip6_tunnel: use skb_cow_head() in ip6_tnl_xmit() To: zhilin zou , Ido Schimmel Cc: Jakub Kicinski , netdev@vger.kernel.org, dsahern@kernel.org, davem@davemloft.net, edumazet@google.com, horms@kernel.org, tom@herbertland.com, vega@nebusec.ai References: <7f099879785257f4d57d6caf9b6308fc76c7aaea.1785734738.git.zhilinz@nebusec.ai> <20260805090721.GA1364862@shredder> <20260805172902.27c9bde0@kernel.org> <20260806085214.GA1748060@shredder> From: Paolo Abeni Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/6/26 11:06 AM, zhilin zou wrote: > On Thu, Aug 6, 2026 at 4:52 PM Ido Schimmel wrote: >> >> On Wed, Aug 05, 2026 at 05:29:02PM -0700, Jakub Kicinski wrote: >>> On Wed, 5 Aug 2026 12:07:21 +0300 Ido Schimmel wrote: >>>> __gre6_xmit() and ip6erspan_tunnel_xmit() already call skb_cow_head() >>>> before calling ip6_tnl_xmit(). >>> >>> Probably just me but can't they all be buggy? >>> PKTGEN likes to send shared skbs around in funny ways. >>> Can we get a good explanation in the commit msg or maybe let's >>> keep the check? >> >> ip6_tnl_xmit() is accessible via two Ethernet devices (pktgen doesn't >> support other types) and they both clear IFF_TX_SKB_SHARING, so if >> pktgen sends them shared skbs, I would say that it's a pktgen bug and >> not a reason to block this patch. Note that pktgen is not available to >> unprivileged users, so it's a less severe bug. >> >> The patch also makes ip6_tnl_xmit() consistent with its IPv4 counterpart >> (ip_tunnel_xmit()) which is already using skb_cow_head(). >> >> Zhiling, please add a note in the commit message that ip6gretap and >> ip6erspan do not expect to be handed shared skbs given that they clear >> IFF_TX_SKB_SHARING. > > Thanks, Ido. I'll add a note to the commit message explaining that > ip6gretap and ip6erspan clear IFF_TX_SKB_SHARING and therefore do not > expect shared skbs, and send a v2 with your Reviewed-by tag retained. I'm not sure if it's too late, but since a v2 is required, I think it would be better to keep the skb_shared check: that will avoid a later patch for the pktgen/shared issue that inevitably will land, possibly via the security channel. Thanks, Paolo