net: add xmit recursion limit to tunnel xmit functions

Tunnel xmit functions (iptunnel_xmit, ip6tunnel_xmit) lack their own
recursion limit. When a bond device in broadcast mode has GRE tap
interfaces as slaves, and those GRE tunnels route back through the
bond, multicast/broadcast traffic triggers infinite recursion between
bond_xmit_broadcast() and ip_tunnel_xmit()/ip6_tnl_xmit(), causing
kernel stack overflow.

The existing XMIT_RECURSION_LIMIT (8) in the no-qdisc path is not
sufficient because tunnel recursion involves route lookups and full IP
output, consuming much more stack per level. Use a lower limit of 4
(IP_TUNNEL_RECURSION_LIMIT) to prevent overflow.

Add recursion detection using dev_xmit_recursion helpers directly in
iptunnel_xmit() and ip6tunnel_xmit() to cover all IPv4/IPv6 tunnel
paths including UDP encapsulated tunnels (VXLAN, Geneve, etc.).

Move dev_xmit_recursion helpers from net/core/dev.h to public header
include/linux/netdevice.h so they can be used by tunnel code.

 BUG: KASAN: stack-out-of-bounds in blake2s.constprop.0+0xe7/0x160
 Write of size 32 at addr ffff88810033fed0 by task kworker/0:1/11
 Workqueue: mld mld_ifc_work
 Call Trace:
  <TASK>
  __build_flow_key.constprop.0 (net/ipv4/route.c:515)
  ip_rt_update_pmtu (net/ipv4/route.c:1073)
  iptunnel_xmit (net/ipv4/ip_tunnel_core.c:84)
  ip_tunnel_xmit (net/ipv4/ip_tunnel.c:847)
  gre_tap_xmit (net/ipv4/ip_gre.c:779)
  dev_hard_start_xmit (net/core/dev.c:3887)
  sch_direct_xmit (net/sched/sch_generic.c:347)
  __dev_queue_xmit (net/core/dev.c:4802)
  bond_dev_queue_xmit (drivers/net/bonding/bond_main.c:312)
  bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5279)
  bond_start_xmit (drivers/net/bonding/bond_main.c:5530)
  dev_hard_start_xmit (net/core/dev.c:3887)
  __dev_queue_xmit (net/core/dev.c:4841)
  ip_finish_output2 (net/ipv4/ip_output.c:237)
  ip_output (net/ipv4/ip_output.c:438)
  iptunnel_xmit (net/ipv4/ip_tunnel_core.c:86)
  gre_tap_xmit (net/ipv4/ip_gre.c:779)
  dev_hard_start_xmit (net/core/dev.c:3887)
  sch_direct_xmit (net/sched/sch_generic.c:347)
  __dev_queue_xmit (net/core/dev.c:4802)
  bond_dev_queue_xmit (drivers/net/bonding/bond_main.c:312)
  bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5279)
  bond_start_xmit (drivers/net/bonding/bond_main.c:5530)
  dev_hard_start_xmit (net/core/dev.c:3887)
  __dev_queue_xmit (net/core/dev.c:4841)
  ip_finish_output2 (net/ipv4/ip_output.c:237)
  ip_output (net/ipv4/ip_output.c:438)
  iptunnel_xmit (net/ipv4/ip_tunnel_core.c:86)
  ip_tunnel_xmit (net/ipv4/ip_tunnel.c:847)
  gre_tap_xmit (net/ipv4/ip_gre.c:779)
  dev_hard_start_xmit (net/core/dev.c:3887)
  sch_direct_xmit (net/sched/sch_generic.c:347)
  __dev_queue_xmit (net/core/dev.c:4802)
  bond_dev_queue_xmit (drivers/net/bonding/bond_main.c:312)
  bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5279)
  bond_start_xmit (drivers/net/bonding/bond_main.c:5530)
  dev_hard_start_xmit (net/core/dev.c:3887)
  __dev_queue_xmit (net/core/dev.c:4841)
  mld_sendpack
  mld_ifc_work
  process_one_work
  worker_thread
  </TASK>

Fixes: 745e20f1b626 ("net: add a recursion limit in xmit path")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Link: https://patch.msgid.link/20260306160133.3852900-2-bestswngs@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 67e25f6d15a4728b6e6bcb0d448fb60b4b89fca9..ae269a2e7f4dd22e4679db7f88b0f6dfedb36115 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3576,17 +3576,49 @@ struct page_pool_bh {
 };
 DECLARE_PER_CPU(struct page_pool_bh, system_page_pool);
 
+#define XMIT_RECURSION_LIMIT   8
+
 #ifndef CONFIG_PREEMPT_RT
 static inline int dev_recursion_level(void)
 {
        return this_cpu_read(softnet_data.xmit.recursion);
 }
+
+static inline bool dev_xmit_recursion(void)
+{
+       return unlikely(__this_cpu_read(softnet_data.xmit.recursion) >
+                       XMIT_RECURSION_LIMIT);
+}
+
+static inline void dev_xmit_recursion_inc(void)
+{
+       __this_cpu_inc(softnet_data.xmit.recursion);
+}
+
+static inline void dev_xmit_recursion_dec(void)
+{
+       __this_cpu_dec(softnet_data.xmit.recursion);
+}
 #else
 static inline int dev_recursion_level(void)
 {
        return current->net_xmit.recursion;
 }
 
+static inline bool dev_xmit_recursion(void)
+{
+       return unlikely(current->net_xmit.recursion > XMIT_RECURSION_LIMIT);
+}
+
+static inline void dev_xmit_recursion_inc(void)
+{
+       current->net_xmit.recursion++;
+}
+
+static inline void dev_xmit_recursion_dec(void)
+{
+       current->net_xmit.recursion--;
+}
 #endif
 
 void __netif_schedule(struct Qdisc *q);

diff --git a/include/net/ip6_tunnel.h b/include/net/ip6_tunnel.h
index 120db2865811250ea9ddbf3bc5396c20a90e1937..1253cbb4b0a45f1c62999be21931ca31b596697f 100644 (file)
--- a/include/net/ip6_tunnel.h
+++ b/include/net/ip6_tunnel.h
@@ -156,6 +156,16 @@ static inline void ip6tunnel_xmit(struct sock *sk, struct sk_buff *skb,
 {
        int pkt_len, err;
 
+       if (dev_recursion_level() > IP_TUNNEL_RECURSION_LIMIT) {
+               net_crit_ratelimited("Dead loop on virtual device %s, fix it urgently!\n",
+                                    dev->name);
+               DEV_STATS_INC(dev, tx_errors);
+               kfree_skb(skb);
+               return;
+       }
+
+       dev_xmit_recursion_inc();
+
        memset(skb->cb, 0, sizeof(struct inet6_skb_parm));
        IP6CB(skb)->flags = ip6cb_flags;
        pkt_len = skb->len - skb_inner_network_offset(skb);
@@ -166,6 +176,8 @@ static inline void ip6tunnel_xmit(struct sock *sk, struct sk_buff *skb,
                        pkt_len = -1;
                iptunnel_xmit_stats(dev, pkt_len);
        }
+
+       dev_xmit_recursion_dec();
 }
 #endif
 #endif

diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
index 4021e6a73e32b80145d9241e4aca5e7881f04c30..80662f81208039feb4fc1d3feae401633af2a5c2 100644 (file)
--- a/include/net/ip_tunnels.h
+++ b/include/net/ip_tunnels.h
@@ -27,6 +27,13 @@
 #include <net/ip6_route.h>
 #endif
 
+/* Recursion limit for tunnel xmit to detect routing loops.
+ * Unlike XMIT_RECURSION_LIMIT (8) used in the no-qdisc path, tunnel
+ * recursion involves route lookups and full IP output, consuming much
+ * more stack per level, so a lower limit is needed.
+ */
+#define IP_TUNNEL_RECURSION_LIMIT      4
+
 /* Keep error state on tunnel for 30 sec */
 #define IPTUNNEL_ERR_TIMEO     (30*HZ)
 

diff --git a/net/core/dev.h b/net/core/dev.h
index 98793a738f43c0e558d2835ab6fb567ed23e5ebb..781619e76b3e8f939f8cbf794287eb9301cba1c8 100644 (file)
--- a/net/core/dev.h
+++ b/net/core/dev.h
@@ -366,41 +366,6 @@ static inline void napi_assert_will_not_race(const struct napi_struct *napi)
 
 void kick_defer_list_purge(unsigned int cpu);
 
-#define XMIT_RECURSION_LIMIT   8
-
-#ifndef CONFIG_PREEMPT_RT
-static inline bool dev_xmit_recursion(void)
-{
-       return unlikely(__this_cpu_read(softnet_data.xmit.recursion) >
-                       XMIT_RECURSION_LIMIT);
-}
-
-static inline void dev_xmit_recursion_inc(void)
-{
-       __this_cpu_inc(softnet_data.xmit.recursion);
-}
-
-static inline void dev_xmit_recursion_dec(void)
-{
-       __this_cpu_dec(softnet_data.xmit.recursion);
-}
-#else
-static inline bool dev_xmit_recursion(void)
-{
-       return unlikely(current->net_xmit.recursion > XMIT_RECURSION_LIMIT);
-}
-
-static inline void dev_xmit_recursion_inc(void)
-{
-       current->net_xmit.recursion++;
-}
-
-static inline void dev_xmit_recursion_dec(void)
-{
-       current->net_xmit.recursion--;
-}
-#endif
-
 int dev_set_hwtstamp_phylib(struct net_device *dev,
                            struct kernel_hwtstamp_config *cfg,
                            struct netlink_ext_ack *extack);

diff --git a/net/ipv4/ip_tunnel_core.c b/net/ipv4/ip_tunnel_core.c
index 2e61ac1371289a7af201100de6d7cafea3c6a2e5..b1b6bf949f65ab7a09ba201d48aa204d913f146d 100644 (file)
--- a/net/ipv4/ip_tunnel_core.c
+++ b/net/ipv4/ip_tunnel_core.c
@@ -58,6 +58,17 @@ void iptunnel_xmit(struct sock *sk, struct rtable *rt, struct sk_buff *skb,
        struct iphdr *iph;
        int err;
 
+       if (dev_recursion_level() > IP_TUNNEL_RECURSION_LIMIT) {
+               net_crit_ratelimited("Dead loop on virtual device %s, fix it urgently!\n",
+                                    dev->name);
+               DEV_STATS_INC(dev, tx_errors);
+               ip_rt_put(rt);
+               kfree_skb(skb);
+               return;
+       }
+
+       dev_xmit_recursion_inc();
+
        skb_scrub_packet(skb, xnet);
 
        skb_clear_hash_if_not_l4(skb);
@@ -88,6 +99,8 @@ void iptunnel_xmit(struct sock *sk, struct rtable *rt, struct sk_buff *skb,
                        pkt_len = 0;
                iptunnel_xmit_stats(dev, pkt_len);
        }
+
+       dev_xmit_recursion_dec();
 }
 EXPORT_SYMBOL_GPL(iptunnel_xmit);