bpf: Make remote_port field in struct bpf_sk_lookup 16-bit wide

commit 9a69e2b upstream. remote_port is another case of a BPF context field documented as a 32-bit value in network byte order for which the BPF context access converter generates a load of a zero-padded 16-bit integer in network byte order. First such case was dst_port in bpf_sock which got addressed in commit 4421a58 ("bpf: Make dst_port field in struct bpf_sock 16-bit wide"). Loading 4-bytes from the remote_port offset and converting the value with bpf_ntohl() leads to surprising results, as the expected value is shifted by 16 bits. Reduce the confusion by splitting the field in two - a 16-bit field holding a big-endian integer, and a 16-bit zero-padding anonymous field that follows it. Suggested-by: Alexei Starovoitov <[email protected]> Signed-off-by: Jakub Sitnicki <[email protected]> Signed-off-by: Alexei Starovoitov <[email protected]> Link: https://lore.kernel.org/bpf/[email protected] Signed-off-by: Greg Kroah-Hartman <[email protected]>
herrnst · Apr 13, 2022 · d4cc2fb · d4cc2fb
1 parent 3cbd531
commit d4cc2fb
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Showing 3 changed files with 6 additions and 4 deletions.
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
@@ -6379,7 +6379,8 @@ 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/net/bpf/test_run.c b/net/bpf/test_run.c
@@ -960,15 +960,15 @@ int bpf_prog_test_run_sk_lookup(struct bpf_prog *prog, const union bpf_attr *kat
 	if (!range_is_zero(user_ctx, offsetofend(typeof(*user_ctx), local_port), sizeof(*user_ctx)))
 		goto out;
 
-	if (user_ctx->local_port > U16_MAX || user_ctx->remote_port > U16_MAX) {
+	if (user_ctx->local_port > U16_MAX) {
 		ret = -ERANGE;
 		goto out;
 	}
 
 	ctx.family = (u16)user_ctx->family;
 	ctx.protocol = (u16)user_ctx->protocol;
 	ctx.dport = (u16)user_ctx->local_port;
-	ctx.sport = (__force __be16)user_ctx->remote_port;
+	ctx.sport = user_ctx->remote_port;
 
 	switch (ctx.family) {
 	case AF_INET:

diff --git a/net/core/filter.c b/net/core/filter.c
@@ -10621,7 +10621,8 @@ static bool sk_lookup_is_valid_access(int off, int size,
 	case bpf_ctx_range(struct bpf_sk_lookup, local_ip4):
 	case bpf_ctx_range_till(struct bpf_sk_lookup, remote_ip6[0], remote_ip6[3]):
 	case bpf_ctx_range_till(struct bpf_sk_lookup, local_ip6[0], local_ip6[3]):
-	case bpf_ctx_range(struct bpf_sk_lookup, remote_port):
+	case offsetof(struct bpf_sk_lookup, remote_port) ...
+	     offsetof(struct bpf_sk_lookup, local_ip4) - 1:
 	case bpf_ctx_range(struct bpf_sk_lookup, local_port):
 	case bpf_ctx_range(struct bpf_sk_lookup, ingress_ifindex):
 		bpf_ctx_record_field_size(info, sizeof(__u32));