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).
3. 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.

Fixes: 7d9c3427894f ("bpf: Make cgroup storages shared between programs on the same cgroup")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/bpf/20260803013934.4036646-1-pulehui@huaweicloud.com

0 files changed, 0 insertions, 0 deletions