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[111.242.220.176]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-198a37c88aasm4985963c88.23.2026.10.24.02.49.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 24 Oct 2026 02:49:56 -0700 (PDT) From: Ting-Han Hou To: stable@vger.kernel.org Cc: David Carlier , Jakub Kicinski Subject: [PATCH 6.6.y] gtp: disable BH before calling udp_tunnel_xmit_skb() Date: Sat, 24 Oct 2026 17:49:49 +0800 Message-ID: <20261024094949.793-1-ue081723@gmail.com> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: David Carlier [ Upstream commit 5638504a2aa9e1b9d72af9060df1a160cce2d379 ] 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 Link: https://patch.msgid.link/20260417055408.4667-1-devnexen@gmail.com Signed-off-by: Jakub Kicinski [ Ting-Han: this tree does not have commit e3411e326fa4 ("net: ipv4: Add a flags argument to iptunnel_xmit(), udp_tunnel_xmit_skb()") or commit 1bec9d0c0046 ("ipv4: Convert ->flowi4_tos to dscp_t."), so the udp_tunnel_xmit_skb() call differs in context; the change is the same ] Assisted-by: LLM Signed-off-by: Ting-Han Hou --- 6f1a9140ecda ("net: add xmit recursion limit to tunnel xmit functions") is in 6.6.160, so the per-CPU recursion counter it added is used from this process-context path there too. Build-tested on v6.6.160 (x86_64, gcc 15.2, CONFIG_GTP=m): no new W=1 or sparse warnings in drivers/net/gtp.c. Not runtime-tested: I could not find an existing tool that sends GTP_CMD_ECHOREQ (libgtpnl does not use it), so the echo request path itself was not exercised. drivers/net/gtp.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c index f0ee46d3c873e..39515aba86e68 100644 --- a/drivers/net/gtp.c +++ b/drivers/net/gtp.c @@ -1827,6 +1827,7 @@ 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, fl4.flowi4_tos, @@ -1836,6 +1837,7 @@ 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); + local_bh_enable(); return 0; } -- 2.53.0