diff options
| author | Jesper Dangaard Brouer | 2018-01-17 11:17:37 +0100 |
|---|---|---|
| committer | Daniel Borkmann | 2018-01-18 01:49:09 +0100 |
| commit | e2e3224122e64ebe15fe02a63e8fe09b64a8c743 (patch) | |
| tree | 398e462dd9fa548b6700ba04de9177c6391a27be /samples | |
| parent | cda18e9726d0f1e280f9e4a19d85ab01c157b414 (diff) | |
samples/bpf: xdp2skb_meta comment explain why pkt-data pointers are invalidated
Improve the 'unknown reason' comment, with an actual explaination of why
the ctx pkt-data pointers need to be loaded after the helper function
bpf_xdp_adjust_meta(). Based on the explaination Daniel gave.
Fixes: 36e04a2d78d9 ("samples/bpf: xdp2skb_meta shows transferring info from XDP to SKB")
Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'samples')
| -rw-r--r-- | samples/bpf/xdp2skb_meta_kern.c | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/samples/bpf/xdp2skb_meta_kern.c b/samples/bpf/xdp2skb_meta_kern.c index 12e1024069c2..0c12048ac79f 100644 --- a/samples/bpf/xdp2skb_meta_kern.c +++ b/samples/bpf/xdp2skb_meta_kern.c @@ -35,15 +35,17 @@ int _xdp_mark(struct xdp_md *ctx) void *data, *data_end; int ret; - /* Reserve space in-front data pointer for our meta info. + /* Reserve space in-front of data pointer for our meta info. * (Notice drivers not supporting data_meta will fail here!) */ ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(*meta)); if (ret < 0) return XDP_ABORTED; - /* For some unknown reason, these ctx pointers must be read - * after bpf_xdp_adjust_meta, else verifier will reject prog. + /* Notice: Kernel-side verifier requires that loading of + * ctx->data MUST happen _after_ helper bpf_xdp_adjust_meta(), + * as pkt-data pointers are invalidated. Helpers that require + * this are determined/marked by bpf_helper_changes_pkt_data() */ data = (void *)(unsigned long)ctx->data; |