6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Zihan Xi commit 006c8b834aed8b02bd8fb9fb05e9e7ead37d1763 upstream. IP-in-IP GSO can re-enter inet_gso_segment() or ipv6_gso_segment() for each nested IP header. encap_level tracks header bytes, not callback depth, so a deep chain can exhaust the kernel stack. Making inet_gso_segment() stackable introduced unbounded IPv4 nesting; IPIP GSO/TSO later made the path reachable. The IPv6 stackable path was introduced separately and uses the same guard. Count IPv4 and IPv6 GSO handler entries in skb_gso_cb, initialized once per top-level GSO operation and preserved across GRE/UDP context changes. Use the existing IP_TUNNEL_RECURSION_LIMIT for both handlers. The first five entries pass, and the sixth returns -EINVAL before dispatching another GSO callback. Fixes: 3347c9602955 ("ipv4: gso: make inet_gso_segment() stackable") Cc: stable@vger.kernel.org Reported-by: Vega Closes: https://lore.kernel.org/all/cover.1790157745.git.zihanx@nebusec.ai/ Assisted-by: LLM Co-developed-by: Luxing Yin Signed-off-by: Luxing Yin Signed-off-by: Zihan Xi Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260924051521.32568-2-zihanx@nebusec.ai Signed-off-by: Paolo Abeni [ Ting-Han: ipv6_gso_segment() still calls ipv6_hopopt_jumbo_remove() right after skb_reset_network_header() in this version; keep the new recursion check directly after skb_reset_network_header() as upstream does, before the jumbo removal ] Signed-off-by: Ting-Han Hou Signed-off-by: Greg Kroah-Hartman --- include/net/gso.h | 8 ++++++++ net/core/gso.c | 1 + net/ipv4/af_inet.c | 3 +++ net/ipv6/ip6_offload.c | 4 ++++ 4 files changed, 16 insertions(+) --- a/include/net/gso.h +++ b/include/net/gso.h @@ -19,10 +19,18 @@ struct skb_gso_cb { int encap_level; __wsum csum; __u16 csum_start; + /* Number of IPv4/IPv6 GSO handler entries for this packet. */ + u8 recursion_counter; }; #define SKB_GSO_CB_OFFSET 32 #define SKB_GSO_CB(skb) ((struct skb_gso_cb *)((skb)->cb + SKB_GSO_CB_OFFSET)) +static inline bool gso_recursion_inc_test(struct sk_buff *skb, + unsigned int limit) +{ + return ++SKB_GSO_CB(skb)->recursion_counter > limit; +} + static inline int skb_tnl_header_len(const struct sk_buff *inner_skb) { return (skb_mac_header(inner_skb) - inner_skb->head) - --- a/net/core/gso.c +++ b/net/core/gso.c @@ -117,6 +117,7 @@ struct sk_buff *__skb_gso_segment(struct SKB_GSO_CB(skb)->mac_offset = skb_headroom(skb); SKB_GSO_CB(skb)->encap_level = 0; + SKB_GSO_CB(skb)->recursion_counter = 0; skb_reset_mac_header(skb); skb_reset_mac_len(skb); --- a/net/ipv4/af_inet.c +++ b/net/ipv4/af_inet.c @@ -1364,6 +1364,9 @@ struct sk_buff *inet_gso_segment(struct int id; skb_reset_network_header(skb); + if (unlikely(gso_recursion_inc_test(skb, + IP_TUNNEL_RECURSION_LIMIT))) + goto out; nhoff = skb_network_header(skb) - skb_mac_header(skb); if (unlikely(!pskb_may_pull(skb, sizeof(*iph)))) goto out; --- a/net/ipv6/ip6_offload.c +++ b/net/ipv6/ip6_offload.c @@ -17,6 +17,7 @@ #include #include #include +#include #include "ip6_offload.h" @@ -120,6 +121,9 @@ static struct sk_buff *ipv6_gso_segment( bool gso_partial; skb_reset_network_header(skb); + if (unlikely(gso_recursion_inc_test(skb, + IP_TUNNEL_RECURSION_LIMIT))) + goto out; err = ipv6_hopopt_jumbo_remove(skb); if (err) return ERR_PTR(err);