bpf: make error reporting in bpf_warn_invalid_xdp_action more clear

Differ between illegal XDP action code and just driver
unsupported one to provide better feedback when we throw
a one-time warning here. Reason is that with 814abfabef3c
("xdp: add bpf_redirect helper function") not all drivers
support the new XDP return code yet and thus they will
fall into their 'default' case when checking for return
codes after program return, which then triggers a
bpf_warn_invalid_xdp_action() stating that the return
code is illegal, but from XDP perspective it's not.

I decided not to place something like a XDP_ACT_MAX define
into uapi i) given we don't have this either for all other
program types, ii) future action codes could have further
encoding there, which would render such define unsuitable
and we wouldn't be able to rip it out again, and iii) we
rarely add new action codes.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index ba848b761cfbf6e90f612e3d9a42c55d657f0ec0..43ab5c402f98f3c2dc15ccc49ec475530a39e401 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -766,8 +766,8 @@ struct bpf_sock {
 
 /* User return codes for XDP prog type.
  * A valid XDP program must return one of these defined values. All other
- * return codes are reserved for future use. Unknown return codes will result
- * in packet drop.
+ * return codes are reserved for future use. Unknown return codes will
+ * result in packet drops and a warning via bpf_warn_invalid_xdp_action().
  */
 enum xdp_action {
        XDP_ABORTED = 0,

diff --git a/net/core/filter.c b/net/core/filter.c
index 0848df2cd9bfdf4fbbd0c93522b2e09efeffe41d..3a50a9b021e208e40f9ac3846bdb93b9b917ad3d 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3609,7 +3609,11 @@ static bool xdp_is_valid_access(int off, int size,
 
 void bpf_warn_invalid_xdp_action(u32 act)
 {
-       WARN_ONCE(1, "Illegal XDP return value %u, expect packet loss\n", act);
+       const u32 act_max = XDP_REDIRECT;
+
+       WARN_ONCE(1, "%s XDP return value %u, expect packet loss!\n",
+                 act > act_max ? "Illegal" : "Driver unsupported",
+                 act);
 }
 EXPORT_SYMBOL_GPL(bpf_warn_invalid_xdp_action);