[PATCH bpf-next v1 0/2] bpf: Fix panic in bpf_get_local_storage

[Jiayuan Chen]

The selftest I provided can reproduce a panic:
'./test_progs -a cgroup_storage_update'

When we attach a program to cgroup and if prog->aux->cgroup_storage
exists, which means the cgroup_storage map is used in the program, we
will then allocate storage by bpf_cgroup_storages_alloc() and assign it
to pl->storage.

At the end, pl->storage will be assigned to
cgrp->bpf.effective[atype]->cgroup_storage by xxx_effective_progs().

But when we attach a program without the cgroup_storage map being used
(prog->aux->cgroup_storage is empty), the cgroup_storage in struct
bpf_prog_array_item is empty.

Then, if we use BPF_LINK_UPDATE to replace the old program with a new one
that uses the cgroup_storage map, we miss the cgroup_storage being
initialized.

This causes a panic when accessing storage in bpf_get_local_storage.

Jiayuan Chen (2):
  bpf: Create cgroup storage if needed when updating link
  selftests/bpf: Add link update test for cgroup_storage

 kernel/bpf/cgroup.c                           | 24 +++++++---
 .../selftests/bpf/prog_tests/cgroup_storage.c | 45 +++++++++++++++++++
 .../selftests/bpf/progs/cgroup_storage.c      |  6 +++
 3 files changed, 70 insertions(+), 5 deletions(-)

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2.47.1