In the Linux kernel, the following vulnerability has been resolved:

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.

https://git.kernel.org/stable/c/183128da0406b1c10e6f60b7b9fe70788b9c8c1d

https://git.kernel.org/stable/c/1921f91298d1388a0bb9db8f83800c998b649cb3

https://git.kernel.org/stable/c/3128b294b426533c8d9162187446d93a8a160359

https://git.kernel.org/stable/c/7bad93e99737e4a5c0c14ac50c05152cf4e28022

https://git.kernel.org/stable/c/866d3d9b87751b1944168fd82615505e0c0fd6cf

https://git.kernel.org/stable/c/acbf45bd584d924b320bee2a7fe2a26f64904d95

https://git.kernel.org/stable/c/ea690b3b6e58ae00979af8195b4cc24df466b65e

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