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Thu, 04 Jul 2024 02:08:18 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHA/v0+krCgjtr2DkeouOKwOhto9pzLiK9iadAlEvA7+g6Hf2UtCDMvBvi1+mRl4tRmFdU5Vg== X-Received: by 2002:a5d:6da8:0:b0:362:4aac:8697 with SMTP id ffacd0b85a97d-3679db7dbdamr780751f8f.0.1720084097811; Thu, 04 Jul 2024 02:08:17 -0700 (PDT) Received: from gerbillo.redhat.com ([2a0d:3344:172b:1510:dd78:6ccd:a776:5943]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-367958d8966sm3260236f8f.91.2024.07.04.02.08.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Jul 2024 02:08:17 -0700 (PDT) Message-ID: Subject: Re: [PATCH net 1/2] net: ioam6: use "new" dst entry with skb_cow_head From: Paolo Abeni To: Justin Iurman , netdev@vger.kernel.org Cc: davem@davemloft.net, dsahern@kernel.org, edumazet@google.com, kuba@kernel.org, linux-kernel@vger.kernel.org Date: Thu, 04 Jul 2024 11:08:15 +0200 In-Reply-To: <20240702174451.22735-2-justin.iurman@uliege.be> References: <20240702174451.22735-1-justin.iurman@uliege.be> <20240702174451.22735-2-justin.iurman@uliege.be> Autocrypt: addr=pabeni@redhat.com; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.4 (3.50.4-1.fc39) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2024-07-02 at 19:44 +0200, Justin Iurman wrote: > In ioam6_output(), we call skb_cow_head() with LL_RESERVED_SPACE(). The > latter uses "dst", which is potentially not the good one anymore. As a > consequence, there might not be enough headroom, depending on the "new" > dev (e.g., needed_headroom > 0). Therefore, we first need to get the > "new" dst entry (from the cache or by calling ip6_route_output()), just > like seg6 and rpl both do, and only then call skb_cow_head() with > LL_RESERVED_SPACE() on the "new" dst entry. >=20 > Fixes: 8cb3bf8bff3c ("ipv6: ioam: Add support for the ip6ip6 encapsulatio= n") > Signed-off-by: Justin Iurman > --- > net/ipv6/ioam6_iptunnel.c | 65 +++++++++++++++++++-------------------- > 1 file changed, 32 insertions(+), 33 deletions(-) >=20 > diff --git a/net/ipv6/ioam6_iptunnel.c b/net/ipv6/ioam6_iptunnel.c > index bf7120ecea1e..b08c13550144 100644 > --- a/net/ipv6/ioam6_iptunnel.c > +++ b/net/ipv6/ioam6_iptunnel.c > @@ -295,7 +295,7 @@ static int ioam6_do_encap(struct net *net, struct sk_= buff *skb, > =20 > static int ioam6_output(struct net *net, struct sock *sk, struct sk_buff= *skb) > { > - struct dst_entry *dst =3D skb_dst(skb); > + struct dst_entry *dst, *orig_dst =3D skb_dst(skb); > struct in6_addr orig_daddr; > struct ioam6_lwt *ilwt; > int err =3D -EINVAL; > @@ -304,7 +304,7 @@ static int ioam6_output(struct net *net, struct sock = *sk, struct sk_buff *skb) > if (skb->protocol !=3D htons(ETH_P_IPV6)) > goto drop; > =20 > - ilwt =3D ioam6_lwt_state(dst->lwtstate); > + ilwt =3D ioam6_lwt_state(orig_dst->lwtstate); > =20 > /* Check for insertion frequency (i.e., "k over n" insertions) */ > pkt_cnt =3D atomic_fetch_inc(&ilwt->pkt_cnt); > @@ -346,45 +346,44 @@ static int ioam6_output(struct net *net, struct soc= k *sk, struct sk_buff *skb) > goto drop; > } > =20 > - err =3D skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev)); > - if (unlikely(err)) > - goto drop; > + local_bh_disable(); > + dst =3D dst_cache_get(&ilwt->cache); > + local_bh_enable(); This makes the dst lookup and cache update unconditional, at best slowing down ioam6_output(), possibly introducing unintended side effects. > + > + if (unlikely(!dst)) { > + struct ipv6hdr *hdr =3D ipv6_hdr(skb); > + struct flowi6 fl6; > + > + memset(&fl6, 0, sizeof(fl6)); > + fl6.daddr =3D hdr->daddr; > + fl6.saddr =3D hdr->saddr; > + fl6.flowlabel =3D ip6_flowinfo(hdr); > + fl6.flowi6_mark =3D skb->mark; > + fl6.flowi6_proto =3D hdr->nexthdr; > + > + dst =3D ip6_route_output(net, NULL, &fl6); > + if (dst->error) { > + err =3D dst->error; > + dst_release(dst); > + goto drop; > + } > =20 > - if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr)) { > local_bh_disable(); > - dst =3D dst_cache_get(&ilwt->cache); > + dst_cache_set_ip6(&ilwt->cache, dst, &fl6.saddr); > local_bh_enable(); > + } > =20 > - if (unlikely(!dst)) { > - struct ipv6hdr *hdr =3D ipv6_hdr(skb); > - struct flowi6 fl6; > - > - memset(&fl6, 0, sizeof(fl6)); > - fl6.daddr =3D hdr->daddr; > - fl6.saddr =3D hdr->saddr; > - fl6.flowlabel =3D ip6_flowinfo(hdr); > - fl6.flowi6_mark =3D skb->mark; > - fl6.flowi6_proto =3D hdr->nexthdr; > - > - dst =3D ip6_route_output(net, NULL, &fl6); > - if (dst->error) { > - err =3D dst->error; > - dst_release(dst); > - goto drop; > - } > - > - local_bh_disable(); > - dst_cache_set_ip6(&ilwt->cache, dst, &fl6.saddr); > - local_bh_enable(); > - } > + skb_dst_drop(skb); > + skb_dst_set(skb, dst); > =20 > - skb_dst_drop(skb); > - skb_dst_set(skb, dst); > + err =3D skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev)); > + if (unlikely(err)) > + goto drop; This is quite a bit of code churn, but you just need to postpone the cow operation after the dst lookup right? I suggest to simply move the cow there, something alike (completely untested):=20 --- diff --git a/net/ipv6/ioam6_iptunnel.c b/net/ipv6/ioam6_iptunnel.c index bf7120ecea1e..636480bded0e 100644 --- a/net/ipv6/ioam6_iptunnel.c +++ b/net/ipv6/ioam6_iptunnel.c @@ -346,10 +346,6 @@ static int ioam6_output(struct net *net, struct sock *= sk, struct sk_buff *skb) goto drop; } =20 - err =3D skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev)); - if (unlikely(err)) - goto drop; - if (!ipv6_addr_equal(&orig_daddr, &ipv6_hdr(skb)->daddr)) { local_bh_disable(); dst =3D dst_cache_get(&ilwt->cache); @@ -381,9 +377,17 @@ static int ioam6_output(struct net *net, struct sock *= sk, struct sk_buff *skb) skb_dst_drop(skb); skb_dst_set(skb, dst); =20 + err =3D skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev)); + if (unlikely(err)) + goto drop; + return dst_output(net, sk, skb); } out: + err =3D skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev)); + if (unlikely(err)) + goto drop; + return dst->lwtstate->orig_output(net, sk, skb); drop: kfree_skb(skb); --- Thanks, Paolo