Re: [PATCH bpf] bpf: fix wrong helper enablement in cgroup local storage

[Roman Gushchin <guro@fb.com>]

On Sat, Oct 27, 2018 at 12:49:02AM +0200, Daniel Borkmann wrote:
> Commit cd3394317653 ("bpf: introduce the bpf_get_local_storage()
> helper function") enabled the bpf_get_local_storage() helper also
> for BPF program types where it does not make sense to use them.
> 
> They have been added both in sk_skb_func_proto() and sk_msg_func_proto()
> even though both program types are not invoked in combination with
> cgroups, and neither through BPF_PROG_RUN_ARRAY(). In the latter the
> bpf_cgroup_storage_set() is set shortly before BPF program invocation.
> 
> Later, the helper bpf_get_local_storage() retrieves this prior set
> up per-cpu pointer and hands the buffer to the BPF program. The map
> argument in there solely retrieves the enum bpf_cgroup_storage_type
> from a local storage map associated with the program and based on the
> type returns either the global or per-cpu storage. However, there
> is no specific association between the program's map and the actual
> content in bpf_cgroup_storage[].
> 
> Meaning, any BPF program that would have been properly run from the
> cgroup side through BPF_PROG_RUN_ARRAY() where bpf_cgroup_storage_set()
> was performed, and that is later unloaded such that prog / maps are
> teared down will cause a use after free if that pointer is retrieved
> from programs that are not run through BPF_PROG_RUN_ARRAY() but have
> the cgroup local storage helper enabled in their func proto.
> 
> Lets just remove it from the two sock_map program types to fix it.
> Auditing through the types where this helper is enabled, it appears
> that these are the only ones where it was mistakenly allowed.
> 
> Fixes: cd3394317653 ("bpf: introduce the bpf_get_local_storage() helper function")
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Roman Gushchin <guro@fb.com>
> Acked-by: John Fastabend <john.fastabend@gmail.com>


Acked-by: Roman Gushchin <guro@fb.com>

Thanks, Daniel!