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 netdevupdatefeatures(). The driver doesn't handle reconfiguring two things at a time very robustly.

Starting with commit 98ba1d931f61 ("bnxt_en: Fix RSS logic in __bnxtreserverings()") 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 (oldrxrings != bp->hwresc.resvrx_rings &&

condition in __bnxtreserverings() will be false. The RSS map won't get updated, and we'll crash with:

BUG: kernel NULL pointer dereference, address: 0000000000000168 RIP: 0010:__bnxthwrmvnic_setrss+0x13a/0x1a0 bnxthwrmvnicrsscfgp5+0x47/0x180 __bnxtsetupvnic_p5+0x58/0x110 bnxtinitnic+0xb72/0xf50 __bnxtopennic+0x40d/0xab0 bnxtopennic+0x2b/0x60 ethtoolsetchannels+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 __bnxtreserverings()") it wasn't causing major issues.