[PATCH bpf] xdp: use trusted arguments in XDP hints kfuncs

[Larysa Zaremba <larysa.zaremba@xxxxxxxxx>]

Currently, verifier does not reject XDP programs that pass NULL pointer to
hints functions. At the same time, this case is not handled in any driver
implementation (including veth). For example, changing

bpf_xdp_metadata_rx_timestamp(ctx, &timestamp);

to

bpf_xdp_metadata_rx_timestamp(ctx, NULL);

in xdp_metadata test successfully crashes the system.

Add KF_TRUSTED_ARGS flag to hints kfunc definitions, so driver code
does not have to worry about getting invalid pointers.

Fixes: 3d76a4d3d4e5 ("bpf: XDP metadata RX kfuncs")
Reported-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
Closes: https://lore.kernel.org/bpf/ZKWo0BbpLfkZHbyE@xxxxxxxxxx/
Signed-off-by: Larysa Zaremba <larysa.zaremba@xxxxxxxxx>
---
 net/core/xdp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 41e5ca8643ec..8362130bf085 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -741,7 +741,7 @@ __bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32 *hash,
 __diag_pop();
 
 BTF_SET8_START(xdp_metadata_kfunc_ids)
-#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, 0)
+#define XDP_METADATA_KFUNC(_, name) BTF_ID_FLAGS(func, name, KF_TRUSTED_ARGS)
 XDP_METADATA_KFUNC_xxx
 #undef XDP_METADATA_KFUNC
 BTF_SET8_END(xdp_metadata_kfunc_ids)
-- 
2.41.0