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([172.56.104.24]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2c7439f85a4sm31747095ad.54.2026.06.20.13.16.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 20 Jun 2026 13:16:14 -0700 (PDT) From: Xiang Mei To: Daniel Borkmann , Martin KaFai Lau , Jesper Dangaard Brouer , Jiayuan Chen , netdev@vger.kernel.org, bpf@vger.kernel.org Cc: John Fastabend , Stanislav Fomichev , Alexei Starovoitov , Jussi Maki , Paolo Abeni , Weiming Shi , Xiang Mei Subject: [PATCH net] net, bpf: check master for NULL in xdp_master_redirect() Date: Sat, 20 Jun 2026 13:15:31 -0700 Message-ID: <20260620201531.180123-1-xmei5@asu.edu> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit xdp_master_redirect() dereferences the result of netdev_master_upper_dev_get_rcu() without a NULL check, but that helper returns NULL when the receiving device has no upper-master adjacency. The reach guard only checks netif_is_bond_slave(). On bond slave release bond_upper_dev_unlink() drops the upper-master adjacency before clearing IFF_SLAVE, so an XDP_TX reaching xdp_master_redirect() in that window still passes netif_is_bond_slave() while master is already NULL, and faults on master->flags at offset 0xb0: BUG: kernel NULL pointer dereference, address: 00000000000000b0 RIP: 0010:xdp_master_redirect (net/core/filter.c:4432) Call Trace: xdp_master_redirect (net/core/filter.c:4432) bpf_prog_run_generic_xdp (include/net/xdp.h:700) do_xdp_generic (net/core/dev.c:5608) __netif_receive_skb_one_core (net/core/dev.c:6204) process_backlog (net/core/dev.c:6319) __napi_poll (net/core/dev.c:7729) net_rx_action (net/core/dev.c:7792) handle_softirqs (kernel/softirq.c:622) __dev_queue_xmit (include/linux/bottom_half.h:33) packet_sendmsg (net/packet/af_packet.c:3082) __sys_sendto (net/socket.c:2252) Kernel panic - not syncing: Fatal exception in interrupt The missing check dates back to the original code; commit 1921f91298d1 ("net, bpf: fix null-ptr-deref in xdp_master_redirect() for down master") later added the master->flags read where the fault now lands but kept the unconditional deref. Check master for NULL before use; a NULL master is treated the same as one that is not up. Fixes: 879af96ffd72 ("net, core: Add support for XDP redirection to slave device") Reported-by: Weiming Shi Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Xiang Mei --- net/core/filter.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/core/filter.c b/net/core/filter.c index 40037413dd4e..6037860d5283 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -4430,7 +4430,7 @@ u32 xdp_master_redirect(struct xdp_buff *xdp) struct net_device *master, *slave; master = netdev_master_upper_dev_get_rcu(xdp->rxq->dev); - if (unlikely(!(master->flags & IFF_UP))) + if (unlikely(!master || !(master->flags & IFF_UP))) return XDP_ABORTED; slave = master->netdev_ops->ndo_xdp_get_xmit_slave(master, xdp); if (slave && slave != xdp->rxq->dev) { -- 2.43.0