| Message ID | 151618425790.21568.15367415527676574003.stgit@firesoul |
|---|---|
| State | Accepted, archived |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [bpf-next] samples/bpf: xdp2skb_meta comment explain why pkt-data pointers are invalidated | expand |
On 01/17/2018 11:17 AM, Jesper Dangaard Brouer wrote: > 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> Applied to bpf-next, thanks for following up on this, Jesper!
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;
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> --- samples/bpf/xdp2skb_meta_kern.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)