[PATCH] gtp: disable BH before calling udp_tunnel_xmit_skb()

David Carlier
2026-04-17T05:54:13Z

gtp_genl_send_echo_req() runs as a generic netlink doit handler in
process context with BH not disabled. It calls udp_tunnel_xmit_skb(),
which eventually invokes iptunnel_xmit() — that uses __this_cpu_inc/dec
on softnet_data.xmit.recursion to track the tunnel xmit recursion level.

Without local_bh_disable(), the task may migrate between
dev_xmit_recursion_inc() and dev_xmit_recursion_dec(), breaking the
per-CPU counter pairing. The result is stale or negative recursion
levels that can later produce false-positive
SKB_DROP_REASON_RECURSION_LIMIT drops on either CPU.

The other udp_tunnel_xmit_skb() call sites in gtp.c are unaffected:
the data path runs under ndo_start_xmit and the echo response handlers
run from the UDP encap rx softirq, both with BH already disabled.

Fix it by disabling BH around the udp_tunnel_xmit_skb() call, mirroring
commit 2cd7e6971fc2 ("sctp: disable BH before calling
udp_tunnel_xmit_skb()").

Fixes: 6f1a9140ecda ("net: add xmit recursion limit to tunnel xmit functions")
Cc: stable@vger.kernel.org
Signed-off-by: David Carlier <devnexen@gmail.com>
---
drivers/net/gtp.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index 70b9e58b9b78..5150f2e4f66b 100644
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -2400,6 +2400,7 @@ static int gtp_genl_send_echo_req(struct sk_buff *skb, struct genl_info *info)
return -ENODEV;
}

+ local_bh_disable();
udp_tunnel_xmit_skb(rt, sk, skb_to_send,
fl4.saddr, fl4.daddr,
inet_dscp_to_dsfield(fl4.flowi4_dscp),
@@ -2409,6 +2410,7 @@ static int gtp_genl_send_echo_req(struct sk_buff *skb, struct genl_info *info)
!net_eq(sock_net(sk),
dev_net(gtp->dev)),
false, 0);
+ local_bh_enable();
return 0;
}

--
2.53.0