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Fri, 03 Oct 2025 05:03:51 -0700 (PDT) Received: from cloudflare.com ([2a09:bac5:5063:2dc::49:214]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6378811ef5esm3893480a12.43.2025.10.03.05.03.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 03 Oct 2025 05:03:50 -0700 (PDT) From: Jakub Sitnicki To: bpf@vger.kernel.org Cc: netdev@vger.kernel.org, kernel-team@cloudflare.com Subject: Re: [PATCH RFC bpf-next 5/9] bpf: Make bpf_skb_vlan_push helper metadata-safe In-Reply-To: <20250929-skb-meta-rx-path-v1-5-de700a7ab1cb@cloudflare.com> (Jakub Sitnicki's message of "Mon, 29 Sep 2025 16:09:10 +0200") References: <20250929-skb-meta-rx-path-v1-0-de700a7ab1cb@cloudflare.com> <20250929-skb-meta-rx-path-v1-5-de700a7ab1cb@cloudflare.com> Date: Fri, 03 Oct 2025 14:03:48 +0200 Message-ID: <87cy742nvf.fsf@cloudflare.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Mon, Sep 29, 2025 at 04:09 PM +02, Jakub Sitnicki wrote: > Use the metadata-aware helper to move packet bytes after skb_push(), > ensuring metadata remains valid after calling the BPF helper. > > Also, take care to reserve sufficient headroom for metadata to fit. > > Signed-off-by: Jakub Sitnicki > --- > include/linux/if_vlan.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h > index 4ecc2509b0d4..b0e1f57d51aa 100644 > --- a/include/linux/if_vlan.h > +++ b/include/linux/if_vlan.h > @@ -355,16 +355,17 @@ static inline int __vlan_insert_inner_tag(struct sk_buff *skb, > __be16 vlan_proto, u16 vlan_tci, > unsigned int mac_len) > { > + const u8 meta_len = mac_len > ETH_HLEN ? skb_metadata_len(skb) : 0; This is a typo. Should be: + const u8 meta_len = mac_len > ETH_TLEN ? skb_metadata_len(skb) : 0; ^^^^^^^^ > struct vlan_ethhdr *veth; > > - if (skb_cow_head(skb, VLAN_HLEN) < 0) > + if (skb_cow_head(skb, meta_len + VLAN_HLEN) < 0) > return -ENOMEM; > > skb_push(skb, VLAN_HLEN); > > /* Move the mac header sans proto to the beginning of the new header. */ > if (likely(mac_len > ETH_TLEN)) > - memmove(skb->data, skb->data + VLAN_HLEN, mac_len - ETH_TLEN); > + skb_postpush_data_move(skb, VLAN_HLEN, mac_len - ETH_TLEN); > if (skb_mac_header_was_set(skb)) > skb->mac_header -= VLAN_HLEN;