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[73.158.218.242]) by smtp.gmail.com with UTF8SMTPSA id d2e1a72fcca58-74af56cb98asm9499219b3a.126.2025.06.30.09.25.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Jun 2025 09:25:42 -0700 (PDT) Date: Mon, 30 Jun 2025 09:25:41 -0700 From: Stanislav Fomichev To: Jakub Sitnicki Cc: bpf@vger.kernel.org, Alexei Starovoitov , Arthur Fabre , Eric Dumazet , Jakub Kicinski , Jesper Dangaard Brouer , Jesse Brandeburg , Joanne Koong , Lorenzo Bianconi , Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= , Yan Zhai , netdev@vger.kernel.org, kernel-team@cloudflare.com, Stanislav Fomichev Subject: Re: [PATCH bpf-next 07/13] net: Clear skb metadata on handover from device to protocol Message-ID: References: <20250630-skb-metadata-thru-dynptr-v1-0-f17da13625d8@cloudflare.com> <20250630-skb-metadata-thru-dynptr-v1-7-f17da13625d8@cloudflare.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250630-skb-metadata-thru-dynptr-v1-7-f17da13625d8@cloudflare.com> On 06/30, Jakub Sitnicki wrote: > With the extension of bpf_dynptr_from_skb(BPF_DYNPTR_F_SKB_METADATA), all > BPF programs authorized to call this kfunc now have access to the skb > metadata area. > > These programs can read up to skb_shinfo(skb)->meta_len bytes located just > before skb_mac_header(skb), regardless of what data is currently there. > > However, as the network stack processes the skb, headers may be added or > removed. Hence, we cannot assume that skb_mac_header() always marks the end > of the metadata area. > > To avoid potential pitfalls, reset the skb metadata length to zero before > passing the skb to the protocol layers. This is a temporary measure until > we can make metadata persist through protocol processing. > > Signed-off-by: Jakub Sitnicki > --- > net/core/dev.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/net/core/dev.c b/net/core/dev.c > index be97c440ecd5..4a2389997535 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -5839,6 +5839,7 @@ static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc, > } > #endif > skb_reset_redirect(skb); > + skb_metadata_clear(skb); And the assumption that it's not gonna break the existing cases is because there is currently no way to read that metadata out afterwards?