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net: add xmit recursion limit to tunnel xmit functions

Browse Source 
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: 745e20f1b6 ("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>
This commit is contained in:
Weiming Shi
2026-03-07 00:01:34 +08:00
committed by Paolo Abeni
parent 3228835877
commit 6f1a9140ec
5 changed files with 64 additions and 35 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
include/linux/netdevice.h
View File

@@ -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);

12
include/net/ip6_tunnel.h
View File

@@ -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

7
include/net/ip_tunnels.h
View File

@@ -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)

35
net/core/dev.h
View File

@@ -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);

13
net/ipv4/ip_tunnel_core.c
View File

@@ -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);