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[93.23.199.162]) by smtp.gmail.com with ESMTPSA id n13sm12792360wms.4.2021.07.07.11.50.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 07 Jul 2021 11:50:23 -0700 (PDT) Subject: Re: [PATCH IPV6 1/1] ipv6: allocate enough headroom in ip6_finish_output2() To: Jakub Kicinski , Eric Dumazet Cc: David Ahern , Vasily Averin , "David S. Miller" , Hideaki YOSHIFUJI , David Ahern , netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <3cb5a2e5-4e4c-728a-252d-4757b6c9612d@virtuozzo.com> <8996db63-5554-d3dc-cd36-94570ade6d18@gmail.com> <20210707094218.0e9b6ffc@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <1cbf3c7b-455e-f3a5-cc2c-c18ce8be4ce1@gmail.com> <20210707113027.4077e544@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> From: Eric Dumazet Message-ID: <0f2c9281-a5fa-f129-ffef-7add5b1d7d02@gmail.com> Date: Wed, 7 Jul 2021 20:50:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210707113027.4077e544@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 7/7/21 8:30 PM, Jakub Kicinski wrote: > On Wed, 7 Jul 2021 19:41:44 +0200 Eric Dumazet wrote: >> On 7/7/21 6:42 PM, Jakub Kicinski wrote: >>> On Wed, 7 Jul 2021 08:45:13 -0600 David Ahern wrote: >>>> why not use hh_len here? >>> >>> Is there a reason for the new skb? Why not pskb_expand_head()? >> >> >> pskb_expand_head() might crash, if skb is shared. >> >> We possibly can add a helper, factorizing all this, >> and eventually use pskb_expand_head() if safe. > > Is there a strategically placed skb_share_check() somewhere further > down? Otherwise there seems to be a lot of questionable skb_cow*() > calls, also __skb_linearize() and skb_pad() are risky, no? > Or is it that shared skbs are uncommon and syzbot doesn't hit them? > Some of us try hard to remove skb_get() occurrences, but they tend to re-appear fast :/ Refs: commit a516993f0ac1694673412eb2d16a091eafa77d2a ("net: fix wrong skb_get() usage / crash in IGMP/MLD parsing code")