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([122.51.212.64]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39d95752809sm15481457a91.13.2026.09.13.07.12.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 13 Sep 2026 07:12:35 -0700 (PDT) From: Zihan Xi To: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, zihanx@nebusec.ai, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, dsahern@kernel.org, idosch@nvidia.com, willemb@google.com, kuniyu@google.com, kees@kernel.org, richardbgobert@gmail.com, jiayuan.chen@linux.dev, stable@vger.kernel.org, Vega , Luxing Yin Subject: [PATCH net 1/1] net: gso: limit recursive IP-in-IP segmentation Date: Sun, 13 Sep 2026 14:12:12 +0000 Message-ID: X-Mailer: git-send-email 2.47.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" IPIP GSO/TSO support makes IP-in-IP GSO dispatch re-enter inet_gso_segment() or ipv6_gso_segment() for every nested IP header. The only state that tracks this nesting is encap_level, which records header bytes and has no recursion bound. A sufficiently deep chain can consume the kernel stack before a transport GSO callback is reached. The unbounded callback nesting was introduced when inet_gso_segment() was made stackable by "ipv4: gso: make inet_gso_segment() stackable". GRE GSO support predated that change, and IP-in-IP GSO/TSO support later made the affected path reachable. Track the number of IP GSO callbacks in skb_gso_cb and reject the 15th callback entry. Thus 14 callback entries are allowed to complete; GSO_RECURSION_LIMIT is the rejection threshold, not the number of successful callbacks. Initialize the counter for each top-level GSO operation and check it in both IPv4 and IPv6 handlers so mixed IP-in-IP nesting is bounded. Fixes: 3347c9602955 ("ipv4: gso: make inet_gso_segment() stackable") Cc: stable@vger.kernel.org Reported-by: Vega Assisted-by: LLM Co-developed-by: Luxing Yin Signed-off-by: Luxing Yin Signed-off-by: Zihan Xi --- include/net/gso.h | 9 +++++++++ net/core/gso.c | 1 + net/ipv4/af_inet.c | 3 +++ net/ipv6/ip6_offload.c | 3 +++ 4 files changed, 16 insertions(+) diff --git a/include/net/gso.h b/include/net/gso.h index 29975440cad5..2665acbb9205 100644 --- a/include/net/gso.h +++ b/include/net/gso.h @@ -19,10 +19,19 @@ struct skb_gso_cb { int encap_level; __wsum csum; __u16 csum_start; + /* Number of GSO callbacks this packet already went through. */ + u8 recursion_counter; }; #define SKB_GSO_CB_OFFSET 32 #define SKB_GSO_CB(skb) ((struct skb_gso_cb *)((skb)->cb + SKB_GSO_CB_OFFS= ET)) =20 +#define GSO_RECURSION_LIMIT 15 /* First callback depth to reject. */ +static inline int gso_recursion_inc_test(struct sk_buff *skb) +{ + return ++SKB_GSO_CB(skb)->recursion_counter =3D=3D + GSO_RECURSION_LIMIT; +} + static inline int skb_tnl_header_len(const struct sk_buff *inner_skb) { return (skb_mac_header(inner_skb) - inner_skb->head) - diff --git a/net/core/gso.c b/net/core/gso.c index bcd156372f4d..e96ef6350064 100644 --- a/net/core/gso.c +++ b/net/core/gso.c @@ -117,6 +117,7 @@ struct sk_buff *__skb_gso_segment(struct sk_buff *skb, =20 SKB_GSO_CB(skb)->mac_offset =3D skb_headroom(skb); SKB_GSO_CB(skb)->encap_level =3D 0; + SKB_GSO_CB(skb)->recursion_counter =3D 0; =20 skb_reset_mac_header(skb); skb_reset_mac_len(skb); diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c index 32d006c1a8ee..2bd88ba05eb9 100644 --- a/net/ipv4/af_inet.c +++ b/net/ipv4/af_inet.c @@ -1374,6 +1374,9 @@ struct sk_buff *inet_gso_segment(struct sk_buff *skb, int ihl; int id; =20 + if (unlikely(gso_recursion_inc_test(skb))) + goto out; + skb_reset_network_header(skb); nhoff =3D skb_network_header(skb) - skb_mac_header(skb); if (unlikely(!pskb_may_pull(skb, sizeof(*iph)))) diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c index 78f50c93c536..391527a1a47b 100644 --- a/net/ipv6/ip6_offload.c +++ b/net/ipv6/ip6_offload.c @@ -103,6 +103,9 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff = *skb, int nhoff; bool gso_partial; =20 + if (unlikely(gso_recursion_inc_test(skb))) + goto out; + skb_reset_network_header(skb); nhoff =3D skb_network_header(skb) - skb_mac_header(skb); if (unlikely(!pskb_may_pull(skb, sizeof(*ipv6h)))) --=20 2.43.0