CVE-2025-21682: eth: bnxt: always recalculate features after XDP clearing, fix null-deref

CVE-2025-21682: eth: bnxt: always recalculate features after XDP clearing, fix null-deref

[Greg Kroah-Hartman]

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2025-21682 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.16 with commit 1054aee82321483dceabbb9b9e5d6512e8fe684b and fixed in 6.12.11 with commit 08831a894d18abfaabb5bbde7c2069a7fb41dd93
	Issue introduced in 4.16 with commit 1054aee82321483dceabbb9b9e5d6512e8fe684b and fixed in 6.13 with commit f0aa6a37a3dbb40b272df5fc6db93c114688adcd

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-21682
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/net/ethernet/broadcom/bnxt/bnxt.c
	drivers/net/ethernet/broadcom/bnxt/bnxt.h
	drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/08831a894d18abfaabb5bbde7c2069a7fb41dd93
	https://git.kernel.org/stable/c/f0aa6a37a3dbb40b272df5fc6db93c114688adcd