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bpf: add cg_skb_is_valid_access for BPF_PROG_TYPE_CGROUP_SKB 

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_end() and
bpf_restore_data_end() 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 <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Song Liu 2018-10-19 09:57:57 -07:00 committed by Alexei Starovoitov
parent 2929ad29a3
commit b39b5f411d
3 changed files with 62 additions and 1 deletions
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21
include/linux/filter.h
View File

@ -548,6 +548,27 @@ 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_end(
struct sk_buff *skb, void **saved_data_end)
{
struct bpf_skb_data_end *cb = (struct bpf_skb_data_end *)skb->cb;
*saved_data_end = cb->data_end;
cb->data_end = skb->data + skb_headlen(skb);
}
/* Restore data saved by bpf_compute_data_pointers(). */
static inline void bpf_restore_data_end(
struct sk_buff *skb, void *saved_data_end)
{
struct bpf_skb_data_end *cb = (struct bpf_skb_data_end *)skb->cb;
cb->data_end = saved_data_end;
}
static inline u8 *bpf_skb_cb(struct sk_buff *skb)
{
/* eBPF programs may read/write skb->cb[] area to transfer meta

6
kernel/bpf/cgroup.c
View File

@ -553,6 +553,7 @@ int __cgroup_bpf_run_filter_skb(struct sock *sk,
{
unsigned int offset = skb->data - skb_network_header(skb);
struct sock *save_sk;
void *saved_data_end;
struct cgroup *cgrp;
int ret;
@ -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_end(skb, &saved_data_end);
ret = BPF_PROG_RUN_ARRAY(cgrp->bpf.effective[type], skb,
bpf_prog_run_save_cb);
bpf_restore_data_end(skb, saved_data_end);
__skb_pull(skb, offset);
skb->sk = save_sk;
return ret == 1 ? 0 : -EPERM;

36
net/core/filter.c
View File

@ -5352,6 +5352,40 @@ 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,
@ -7044,7 +7078,7 @@ 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,
};