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 doesnt 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 doesnt 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 wont get updated, and well 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 wasnt causing major issues.

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/08831a894d18abfaabb5bbde7c2069a7fb41dd93
• https://git.kernel.org/stable/c/f0aa6a37a3dbb40b272df5fc6db93c114688adcd