From 0cdbb4b09a0658b72c563638d476113aadd91afb Mon Sep 17 00:00:00 2001 From: =?utf8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= Date: Fri, 28 Jun 2019 11:12:35 +0200 Subject: [PATCH] devmap: Allow map lookups from eBPF MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit We don't currently allow lookups into a devmap from eBPF, because the map lookup returns a pointer directly to the dev->ifindex, which shouldn't be modifiable from eBPF. However, being able to do lookups in devmaps is useful to know (e.g.) whether forwarding to a specific interface is enabled. Currently, programs work around this by keeping a shadow map of another type which indicates whether a map index is valid. Since we now have a flag to make maps read-only from the eBPF side, we can simply lift the lookup restriction if we make sure this flag is always set. Signed-off-by: Toke Høiland-Jørgensen Acked-by: Jonathan Lemon Acked-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann --- kernel/bpf/devmap.c | 5 +++++ kernel/bpf/verifier.c | 7 ++----- 2 files changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c index a4dddc867cbf..d83cf8ccc872 100644 --- a/kernel/bpf/devmap.c +++ b/kernel/bpf/devmap.c @@ -89,6 +89,11 @@ static struct bpf_map *dev_map_alloc(union bpf_attr *attr) attr->value_size != 4 || attr->map_flags & ~DEV_CREATE_FLAG_MASK) return ERR_PTR(-EINVAL); + /* Lookup returns a pointer straight to dev->ifindex, so make sure the + * verifier prevents writes from the BPF side + */ + attr->map_flags |= BPF_F_RDONLY_PROG; + dtab = kzalloc(sizeof(*dtab), GFP_USER); if (!dtab) return ERR_PTR(-ENOMEM); diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 6b5623d320f9..9b6ee93d5a85 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3414,12 +3414,9 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env, if (func_id != BPF_FUNC_get_local_storage) goto error; break; - /* devmap returns a pointer to a live net_device ifindex that we cannot - * allow to be modified from bpf side. So do not allow lookup elements - * for now. - */ case BPF_MAP_TYPE_DEVMAP: - if (func_id != BPF_FUNC_redirect_map) + if (func_id != BPF_FUNC_redirect_map && + func_id != BPF_FUNC_map_lookup_elem) goto error; break; /* Restrict bpf side of cpumap and xskmap, open when use-cases -- 2.30.2