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.

This vulnerability is rated as Moderate because exploitation is limited to a local denial of service and requires administrative privileges (specifically CAP_NET_ADMIN) to modify network interface configurations. The issue only affects systems equipped with Broadcom NetXtreme network adapters utilizing the bnxt_en driver. An attacker must perform a specific sequence of operations—detaching an XDP program followed by altering channel settings—to trigger the kernel crash, limiting the overall blast radius under typical operational deployments.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.