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.
Two helper functions bpf_compute_and_save_data_pointers() and
bpf_restore_data_pointers() are introduced. There are used in
__cgroup_bpf_run_filter_skb(), to compute proper data_end for the
BPF program, and restore original data afterwards.
Signed-off-by: Song Liu <songliubrav...@fb.com>
---
include/linux/filter.h | 24 ++++++++++++++++++++++++
kernel/bpf/cgroup.c | 6 ++++++
net/core/filter.c | 36 +++++++++++++++++++++++++++++++++++-
3 files changed, 65 insertions(+), 1 deletion(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 5771874bc01e..96b3ee7f14c9 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -548,6 +548,30 @@ static inline void bpf_compute_data_pointers(struct
sk_buff *skb)
cb->data_end = skb->data + skb_headlen(skb);
}
+/* Similar to bpf_compute_data_pointers(), except that save orginal
+ * data in cb->data and cb->meta_data for restore.
+ */
+static inline void bpf_compute_and_save_data_pointers(
+ struct sk_buff *skb, void *saved_pointers[2])
+{
+ struct bpf_skb_data_end *cb = (struct bpf_skb_data_end *)skb->cb;
+
+ saved_pointers[0] = cb->data_meta;
+ saved_pointers[1] = cb->data_end;
+ cb->data_meta = skb->data - skb_metadata_len(skb);
+ cb->data_end = skb->data + skb_headlen(skb);
+}
+
+/* Restore data saved by bpf_compute_data_pointers(). */
+static inline void bpf_restore_data_pointers(
+ struct sk_buff *skb, void *saved_pointers[2])
+{
+ struct bpf_skb_data_end *cb = (struct bpf_skb_data_end *)skb->cb;
+
+ cb->data_meta = saved_pointers[0];
+ cb->data_end = saved_pointers[1];;
+}
+
static inline u8 *bpf_skb_cb(struct sk_buff *skb)
{
/* eBPF programs may read/write skb->cb[] area to transfer meta
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 00f6ed2e4f9a..5f5180104ddc 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -554,6 +554,7 @@ int __cgroup_bpf_run_filter_skb(struct sock *sk,
unsigned int offset = skb->data - skb_network_header(skb);
struct sock *save_sk;
struct cgroup *cgrp;
+ void *saved_pointers[2];
int ret;
if (!sk || !sk_fullsock(sk))
@@ -566,8 +567,13 @@ 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_and_save_data_pointers(skb, saved_pointers);
+
ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], skb,
bpf_prog_run_save_cb);
+ bpf_restore_data_pointers(skb, saved_pointers);
__skb_pull(skb, offset);
skb->sk = save_sk;
return ret == 1 ? 0 : -EPERM;
diff --git a/net/core/filter.c b/net/core/filter.c
index 1a3ac6c46873..e3ca30bd6840 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5346,6 +5346,40 @@ 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)
+{
+ switch (off) {
+ case bpf_ctx_range(struct __sk_buff, tc_classid):
+ case bpf_ctx_range(struct __sk_buff, data_meta):
+ case bpf_ctx_range(struct __sk_buff, flow_keys):
+ return false;
+ }
+ if (type == BPF_WRITE) {
+ switch (off) {
+ case bpf_ctx_range(struct __sk_buff, mark):
+ case bpf_ctx_range(struct __sk_buff, priority):
+ case bpf_ctx_range_till(struct __sk_buff, cb[0], cb[4]):
+ break;
+ default:
+ return false;
+ }
+ }
+
+ switch (off) {
+ 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;
+ }
+
+ 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 +7072,7 @@ 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
