[PATCH bpf-next 1/2] bpf: add cg_skb_is_valid_access for BPF_PROG_TYPE_CGROUP_SKB

[Song Liu <songliubraving@fb.com>]

BPF programs of BPF_PROG_TYPE_CGROUP_SKB need to access headers in the
skb. This patch enables direct access of skb for these programs.

In __cgroup_bpf_run_filter_skb(), bpf_compute_data_pointers() is called
to compute proper data_end for the BPF program.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 kernel/bpf/cgroup.c |  4 ++++
 net/core/filter.c   | 26 +++++++++++++++++++++++++-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 00f6ed2e4f9a..340d496f35bd 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -566,6 +566,10 @@ int __cgroup_bpf_run_filter_skb(struct sock *sk,
 	save_sk = skb->sk;
 	skb->sk = sk;
 	__skb_push(skb, offset);
+
+	/* compute pointers for the bpf prog */
+	bpf_compute_data_pointers(skb);
+
 	ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], skb,
 				 bpf_prog_run_save_cb);
 	__skb_pull(skb, offset);
diff --git a/net/core/filter.c b/net/core/filter.c
index 1a3ac6c46873..8b5a502e241f 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5346,6 +5346,30 @@ static bool sk_filter_is_valid_access(int off, int size,
 	return bpf_skb_is_valid_access(off, size, type, prog, info);
 }
 
+static bool cg_skb_is_valid_access(int off, int size,
+				   enum bpf_access_type type,
+				   const struct bpf_prog *prog,
+				   struct bpf_insn_access_aux *info)
+{
+	if (type == BPF_WRITE)
+		return false;
+
+	switch (off) {
+	case bpf_ctx_range(struct __sk_buff, len):
+		break;
+	case bpf_ctx_range(struct __sk_buff, data):
+		info->reg_type = PTR_TO_PACKET;
+		break;
+	case bpf_ctx_range(struct __sk_buff, data_end):
+		info->reg_type = PTR_TO_PACKET_END;
+		break;
+	default:
+		return false;
+	}
+
+	return bpf_skb_is_valid_access(off, size, type, prog, info);
+}
+
 static bool lwt_is_valid_access(int off, int size,
 				enum bpf_access_type type,
 				const struct bpf_prog *prog,
@@ -7038,7 +7062,7 @@ const struct bpf_prog_ops xdp_prog_ops = {
 
 const struct bpf_verifier_ops cg_skb_verifier_ops = {
 	.get_func_proto		= cg_skb_func_proto,
-	.is_valid_access	= sk_filter_is_valid_access,
+	.is_valid_access	= cg_skb_is_valid_access,
 	.convert_ctx_access	= bpf_convert_ctx_access,
 };
 
-- 
2.17.1