On Mon, Mar 09, 2026 at 11:06:58AM +0800, Jiayuan Chen wrote: > From: Jiayuan Chen <[email protected]> > > bond_rr_gen_slave_id() dereferences bond->rr_tx_counter without a NULL > check. rr_tx_counter is a per-CPU counter only allocated in bond_open() > when the bond mode is round-robin. If the bond device was never brought > up, rr_tx_counter remains NULL, causing a null-ptr-deref. > > The XDP redirect path can reach this code even when the bond is not up: > bpf_master_redirect_enabled_key is a global static key, so when any bond > device has native XDP attached, the XDP_TX -> xdp_master_redirect() > interception is enabled for all bond slaves system-wide. This allows the > path xdp_master_redirect() -> bond_xdp_get_xmit_slave() -> > bond_xdp_xmit_roundrobin_slave_get() -> bond_rr_gen_slave_id() to be > reached on a bond that was never opened. > > Fix this by adding a NULL check with unlikely() in bond_rr_gen_slave_id() > before dereferencing rr_tx_counter. When rr_tx_counter is NULL (bond was > never opened), fall back to get_random_u32() for slave selection. The > allocation in bond_open() is kept, with WRITE_ONCE() added to safely > publish the pointer to the XDP read side. A plain read suffices for the > !bond->rr_tx_counter guard in bond_open() itself, as bond_open() runs > under RTNL lock and is the only writer of rr_tx_counter. > > Fixes: 879af96ffd72 ("net, core: Add support for XDP redirection to slave > device") > Reported-by: [email protected] > Closes: > https://lore.kernel.org/all/[email protected]/T/ > Signed-off-by: Jiayuan Chen <[email protected]> > --- > drivers/net/bonding/bond_main.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) >
This is Jay's patch + the unlikely change, looks good to me. Reviewed-by: Nikolay Aleksandrov <[email protected]> Cheers, Nik > diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c > index 444519078da3..b8ec87625ce3 100644 > --- a/drivers/net/bonding/bond_main.c > +++ b/drivers/net/bonding/bond_main.c > @@ -4290,9 +4290,11 @@ static int bond_open(struct net_device *bond_dev) > struct slave *slave; > > if (BOND_MODE(bond) == BOND_MODE_ROUNDROBIN && !bond->rr_tx_counter) { > - bond->rr_tx_counter = alloc_percpu(u32); > - if (!bond->rr_tx_counter) > + u32 __percpu *rr_tx_tmp = alloc_percpu(u32); > + > + if (!rr_tx_tmp) > return -ENOMEM; > + WRITE_ONCE(bond->rr_tx_counter, rr_tx_tmp); > } > > /* reset slave->backup and slave->inactive */ > @@ -4883,6 +4885,9 @@ static u32 bond_rr_gen_slave_id(struct bonding *bond) > struct reciprocal_value reciprocal_packets_per_slave; > int packets_per_slave = bond->params.packets_per_slave; > > + if (unlikely(!READ_ONCE(bond->rr_tx_counter))) > + return get_random_u32(); > + > switch (packets_per_slave) { > case 0: > slave_id = get_random_u32(); > -- > 2.43.0 >
