selftests/bpf: Cover 4-byte load from remote_port in bpf_sk_lookup

Extend the context access tests for sk_lookup prog to cover the surprising
case of a 4-byte load from the remote_port field, where the expected value
is actually shifted by 16 bits.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220209184333.654927-3-jakub@cloudflare.com

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index a7f0dde..afe3d0d 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6453,7 +6453,8 @@ struct bpf_sk_lookup {
        __u32 protocol;         /* IP protocol (IPPROTO_TCP, IPPROTO_UDP) */
        __u32 remote_ip4;       /* Network byte order */
        __u32 remote_ip6[4];    /* Network byte order */
-       __u32 remote_port;      /* Network byte order */
+       __be16 remote_port;     /* Network byte order */
+       __u16 :16;              /* Zero padding */
        __u32 local_ip4;        /* Network byte order */
        __u32 local_ip6[4];     /* Network byte order */
        __u32 local_port;       /* Host byte order */

diff --git a/tools/testing/selftests/bpf/progs/test_sk_lookup.c b/tools/testing/selftests/bpf/progs/test_sk_lookup.c
index 83b0aaa..bf5b7ca 100644 (file)
--- a/tools/testing/selftests/bpf/progs/test_sk_lookup.c
+++ b/tools/testing/selftests/bpf/progs/test_sk_lookup.c
@@ -392,6 +392,7 @@ int ctx_narrow_access(struct bpf_sk_lookup *ctx)
 {
        struct bpf_sock *sk;
        int err, family;
+       __u32 val_u32;
        bool v4;
 
        v4 = (ctx->family == AF_INET);
@@ -418,6 +419,11 @@ int ctx_narrow_access(struct bpf_sk_lookup *ctx)
        if (LSW(ctx->remote_port, 0) != SRC_PORT)
                return SK_DROP;
 
+       /* Load from remote_port field with zero padding (backward compatibility) */
+       val_u32 = *(__u32 *)&ctx->remote_port;
+       if (val_u32 != bpf_htonl(bpf_ntohs(SRC_PORT) << 16))
+               return SK_DROP;
+
        /* Narrow loads from local_port field. Expect DST_PORT. */
        if (LSB(ctx->local_port, 0) != ((DST_PORT >> 0) & 0xff) ||
            LSB(ctx->local_port, 1) != ((DST_PORT >> 8) & 0xff) ||