CVE-2025-21682

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

eth: bnxt: always recalculate features after XDP clearing, fix null-deref

Recalculate features when XDP is detached.

Before:

# ip li set dev eth0 xdp obj xdp_dummy.bpf.o sec xdp

# ip li set dev eth0 xdp off

# ethtool -k eth0 | grep gro

rx-gro-hw: off [requested on]

After:

# ip li set dev eth0 xdp obj xdp_dummy.bpf.o sec xdp

# ip li set dev eth0 xdp off

# ethtool -k eth0 | grep gro

rx-gro-hw: on

The fact that HW-GRO doesn't get re-enabled automatically is just

a minor annoyance. The real issue is that the features will randomly

come back during another reconfiguration which just happens to invoke

netdev_update_features(). The driver doesn't handle reconfiguring

two things at a time very robustly.

Starting with commit 98ba1d931f61 ("bnxt_en: Fix RSS logic in

__bnxt_reserve_rings()") we only reconfigure the RSS hash table

if the "effective" number of Rx rings has changed. If HW-GRO is

enabled "effective" number of rings is 2x what user sees.

So if we are in the bad state, with HW-GRO re-enablement "pending"

after XDP off, and we lower the rings by / 2 - the HW-GRO rings

doing 2x and the ethtool -L doing / 2 may cancel each other out,

and the:

if (old_rx_rings != bp->hw_resc.resv_rx_rings &&

condition in __bnxt_reserve_rings() will be false.

The RSS map won't get updated, and we'll crash with:

BUG: kernel NULL pointer dereference, address: 0000000000000168

RIP: 0010:__bnxt_hwrm_vnic_set_rss+0x13a/0x1a0

bnxt_hwrm_vnic_rss_cfg_p5+0x47/0x180

__bnxt_setup_vnic_p5+0x58/0x110

bnxt_init_nic+0xb72/0xf50

__bnxt_open_nic+0x40d/0xab0

bnxt_open_nic+0x2b/0x60

ethtool_set_channels+0x18c/0x1d0

As we try to access a freed ring.

The issue is present since XDP support was added, really, but

prior to commit 98ba1d931f61 ("bnxt_en: Fix RSS logic in

__bnxt_reserve_rings()") it wasn't causing major issues.