bpf: Fix stale offload->prog pointer after constant blinding

Overview

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

bpf: Fix stale offload->prog pointer after constant blinding

When a dev-bound-only BPF program (BPF_F_XDP_DEV_BOUND_ONLY) undergoes JIT compilation with constant blinding enabled (bpf_jit_harden >= 2), bpf_jit_blind_constants() clones the program. The original prog is then freed in bpf_jit_prog_release_other(), which updates aux->prog to point to the surviving clone, but fails to update offload->prog.

This leaves offload->prog pointing to the freed original program. When the network namespace is subsequently destroyed, cleanup_net() triggers bpf_dev_bound_netdev_unregister(), which iterates ondev->progs and calls __bpf_prog_offload_destroy(offload->prog). Accessing the freed prog causes a page fault:

BUG: unable to handle page fault for address: ffffc900085f1038 Workqueue: netns cleanup_net RIP: 0010:__bpf_prog_offload_destroy+0xc/0x80 Call Trace: __bpf_offload_dev_netdev_unregister+0x257/0x350 bpf_dev_bound_netdev_unregister+0x4a/0x90 unregister_netdevice_many_notify+0x2a2/0x660 ... cleanup_net+0x21a/0x320

The test sequence that triggers this reliably is:

1. Set net.core.bpf_jit_harden=2 (echo 2 > /proc/sys/net/core/bpf_jit_harden)
2. Run xdp_metadata selftest, which creates a dev-bound-only XDP program on a veth inside a netns (./test_progs -t xdp_metadata)
3. cleanup_net -> page fault in __bpf_prog_offload_destroy

Dev-bound-only programs are unique in that they have an offload structure but go through the normal JIT path instead of bpf_prog_offload_compile(). This means they are subject to constant blinding's prog clone-and-replace, while also having offload->prog that must stay in sync.

Fix this by updating offload->prog in bpf_jit_prog_release_other(), alongside the existing aux->prog update. Both are back-pointers to the prog that must be kept in sync when the prog is replaced.

Affected

• Linux >= 2b3486bc2d237ec345b3942b7be5deabf8c8fed1 < a713b72ff88cdab4d5d692908ab1259ada511f4d
• Linux >= 2b3486bc2d237ec345b3942b7be5deabf8c8fed1 < 25484c39d1ec82a0368798d956da3de5039b3fe8
• Linux >= 2b3486bc2d237ec345b3942b7be5deabf8c8fed1 < 059525cf18e69a9313baf947d8898c6ee7ca6b65
• Linux >= 2b3486bc2d237ec345b3942b7be5deabf8c8fed1 < c79f8503d83d4665be461fb9e45e215d0380c67b
• Linux >= 2b3486bc2d237ec345b3942b7be5deabf8c8fed1 < a1aa9ef47c299c5bbc30594d3c2f0589edf908e6
• Linux 6.3

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.