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Sat, 15 Aug 2026 20:52:51 -0700 (PDT) From: "Cen Zhang (Microsoft)" To: pablo@netfilter.org, laforge@gnumonks.org, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com Cc: osmocom-net-gprs@lists.osmocom.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, tgopinath@linux.microsoft.com, kys@microsoft.com, blbllhy@gmail.com, "Xiang Mei (Microsoft)" Subject: [PATCH net] gtp: fix NULL pointer dereference in gtp0_handle_echo_resp() Date: Sat, 15 Aug 2026 23:52:05 -0400 Message-ID: <20260816035205.57966-1-blbllhy@gmail.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In gtp_create_sockets(), gtp->sk_created is set to true before gtp->sk0 and gtp->sk1u are assigned. A concurrent GTP Echo Response packet on another CPU observes sk_created == true and dereferences the still-NULL gtp->sk0 in gtp0_handle_echo_resp(), causing a kernel panic. KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] RIP: 0010:gtp_encap_recv (drivers/net/gtp.c:542 gtp0_handle_echo_resp) Call Trace: udp_queue_rcv_one_skb ip_protocol_deliver_rcu ip_local_deliver Kernel panic - not syncing: Fatal exception in interrupt Reorder the assignments so that gtp->sk0 and gtp->sk1u are fully visible before gtp->sk_created is set to true. This ensures no concurrent packet path can observe the flag without valid socket pointers. Fixes: b20dc3c68458 ("gtp: Allow to create GTP device without FDs") Reported-by: AutonomousCodeSecurity@microsoft.com Reported-by: Xiang Mei (Microsoft) Reported-by: Cen Zhang (Microsoft) Signed-off-by: Cen Zhang (Microsoft) --- drivers/net/gtp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c index 9a12cc53da00..2b5a8f6d24d0 100644 --- a/drivers/net/gtp.c +++ b/drivers/net/gtp.c @@ -1456,9 +1456,9 @@ static int gtp_create_sockets(struct gtp_dev *gtp, const struct nlattr *nla, return PTR_ERR(sk1u); } - gtp->sk_created = true; gtp->sk0 = sk0; gtp->sk1u = sk1u; + gtp->sk_created = true; return 0; } -- 2.52.0