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bpf: add cg_skb_is_valid_access for BPF_PROG_TYPE_CGROUP_SKB

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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
commit b39b5f411d
3 changed files with 62 additions and 1 deletions
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6
kernel/bpf/cgroup.c
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@ -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;