Linux EUVD-2026-81974

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

bpf, cgroup: Fix invalid storage access after __cgroup_bpf_attach failed

A potential invalid storage access issue can occur after replacing a cgroup bpf prog.

This occurs in the following scenario:

1. prog1 with storage is attached to a cgroup in multi-attach mode.
2. prog1 is replaced with prog2 using BPF_F_REPLACE in multi-attach

mode, but fails midway (e.g. in bpf_trampoline_link_cgroup_shim or update_effective_progs).

1. A new prog3 is attached to the cgroup in multi-attach mode.

The reason is that __cgroup_bpf_attach overwrites pl->storage with the new storage prior to attachment completion. When attachment fails midway, the cleanup path calls bpf_cgroup_storages_free(new_storage) to free the newly allocated storage, but fails to restore pl->storage back to old_storage.

Consequently, the still-active prog1 holds invalid or dangling storage pointers, leading to an invalid memory access when prog1 executes and calls bpf_get_local_storage. Additionally, original pl->flags and cgrp->bpf.flags[atype] are left unrestored.

Fix this by saving old_pl_flags, old_storage, and old_flags prior to the update, and properly restoring all of them in the cleanup path on error.