[bpf-next,v3,3/3] devmap: Allow map lookups from eBPF
diff mbox series

Message ID 156026784018.26748.12066708200377212358.stgit@alrua-x1
State Changes Requested
Delegated to: BPF Maintainers
Headers show
  • xdp: Allow lookup into devmaps before redirect
Related show

Commit Message

Toke Høiland-Jørgensen June 11, 2019, 3:44 p.m. UTC
From: Toke Høiland-Jørgensen <toke@redhat.com>

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>
 kernel/bpf/devmap.c   |    5 +++++
 kernel/bpf/verifier.c |    7 ++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff mbox series

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index c945518225f3..83c77f43030d 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -99,6 +99,11 @@  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 5c2cb5bd84ce..7128a9821481 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2893,12 +2893,9 @@  static int check_map_func_compatibility(struct bpf_verifier_env *env,
 		if (func_id != BPF_FUNC_get_local_storage)
 			goto error;
-	/* 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.
-	 */
-		if (func_id != BPF_FUNC_redirect_map)
+		if (func_id != BPF_FUNC_redirect_map &&
+		    func_id != BPF_FUNC_map_lookup_elem)
 			goto error;
 	/* Restrict bpf side of cpumap and xskmap, open when use-cases