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authorJesper Dangaard Brouer <brouer@redhat.com>2018-01-17 11:17:37 +0100
committerDaniel Borkmann <daniel@iogearbox.net>2018-01-18 01:49:09 +0100
commite2e3224122e64ebe15fe02a63e8fe09b64a8c743 (patch)
tree398e462dd9fa548b6700ba04de9177c6391a27be
parentcda18e9726d0f1e280f9e4a19d85ab01c157b414 (diff)
downloadlinux-e2e3224122e64ebe15fe02a63e8fe09b64a8c743.tar.gz
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>
-rw-r--r--samples/bpf/xdp2skb_meta_kern.c8
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;