From: Jiayuan Chen Date: Sat, 11 Apr 2026 00:55:19 +0000 (+0800) Subject: net, bpf: fix null-ptr-deref in xdp_master_redirect() for down master X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=1921f91298d1388a0bb9db8f83800c998b649cb3;p=thirdparty%2Fkernel%2Flinux.git net, bpf: fix null-ptr-deref in xdp_master_redirect() for down master syzkaller reported a kernel panic in bond_rr_gen_slave_id() reached via xdp_master_redirect(). Full decoded trace: https://syzkaller.appspot.com/bug?extid=80e046b8da2820b6ba73 bond_rr_gen_slave_id() dereferences bond->rr_tx_counter, a per-CPU counter that bonding only allocates in bond_open() when the mode is round-robin. If the bond device was never brought up, rr_tx_counter stays NULL. The XDP redirect path can still reach that code on a bond that was never opened: bpf_master_redirect_enabled_key is a global static key, so as soon as any bond device has native XDP attached, the XDP_TX -> xdp_master_redirect() interception is enabled for every slave system-wide. The path xdp_master_redirect() -> bond_xdp_get_xmit_slave() -> bond_xdp_xmit_roundrobin_slave_get() -> bond_rr_gen_slave_id() then runs against a bond that has no rr_tx_counter and crashes. Fix this in the generic xdp_master_redirect() by refusing to call into the master's ->ndo_xdp_get_xmit_slave() when the master device is not up. IFF_UP is only set after ->ndo_open() has successfully returned, so this reliably excludes masters whose XDP state has not been fully initialized. Drop the frame with XDP_ABORTED so the exception is visible via trace_xdp_exception() rather than silently falling through. This is not specific to bonding: any current or future master that defers XDP state allocation to ->ndo_open() is protected. Fixes: 879af96ffd72 ("net, core: Add support for XDP redirection to slave device") Reported-by: syzbot+80e046b8da2820b6ba73@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/698f84c6.a70a0220.2c38d7.00cc.GAE@google.com/T/ Suggested-by: Daniel Borkmann Acked-by: Daniel Borkmann Signed-off-by: Jiayuan Chen Link: https://patch.msgid.link/20260411005524.201200-2-jiayuan.chen@linux.dev Signed-off-by: Paolo Abeni --- diff --git a/net/core/filter.c b/net/core/filter.c index 53ce06ed4a88e..90ae4f314b6c3 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -4395,6 +4395,8 @@ 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))) + return XDP_ABORTED; slave = master->netdev_ops->ndo_xdp_get_xmit_slave(master, xdp); if (slave && slave != xdp->rxq->dev) { /* The target device is different from the receiving device, so