devmap: Allow map lookups from eBPF (0cdbb4b0) · Commits · 戴 / test

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 <toke@redhat.com> Acked-by:

Jonathan Lemon <jonathan.lemon@gmail.com> Acked-by:

Andrii Nakryiko <andriin@fb.com> Signed-off-by:

Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/devmap.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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);

kernel/bpf/verifier.c

+2 −5

Original line number	Diff line number	Diff line
		@@ -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

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