Merge branch 'Add skb_adjust_room() for SK_SKB'

John Fastabend says:

====================
This implements the helper skb_adjust_room() for BPF_SKS_SK_STREAM_VERDICT
programs so we can push/pop headers from the data on recieve. One use
case is to pop TLS headers off kTLS packets.

The first patch implements the helper and the second updates test_sockmap
to use it removing some case handling we had to do earlier to account for
the TLS headers in the kTLS tests.

v1->v2:
 Fix error path for TLS case (Daniel)
 check mode input is 0 because we don't use it now (Daniel)
 Remove incorrect/misleading comment (Lorenz)

Thanks,
John
Acked-by: Martin KaFai Lau <kafai@fb.com>
---
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

net/core/filter.c

@@ -76,6 +76,7 @@
 #include <net/bpf_sk_storage.h>
 #include <net/transp_v6.h>
 #include <linux/btf_ids.h>
+#include <net/tls.h>
 
 static const struct bpf_func_proto *
 bpf_sk_base_func_proto(enum bpf_func_id func_id);
@@ -3479,6 +3480,48 @@ static u32 __bpf_skb_max_len(const struct sk_buff *skb)
 			  SKB_MAX_ALLOC;
 }
 
+BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
+	   u32, mode, u64, flags)
+{
+	u32 len_diff_abs = abs(len_diff);
+	bool shrink = len_diff < 0;
+	int ret = 0;
+
+	if (unlikely(flags || mode))
+		return -EINVAL;
+	if (unlikely(len_diff_abs > 0xfffU))
+		return -EFAULT;
+
+	if (!shrink) {
+		ret = skb_cow(skb, len_diff);
+		if (unlikely(ret < 0))
+			return ret;
+		__skb_push(skb, len_diff_abs);
+		memset(skb->data, 0, len_diff_abs);
+	} else {
+		if (unlikely(!pskb_may_pull(skb, len_diff_abs)))
+			return -ENOMEM;
+		__skb_pull(skb, len_diff_abs);
+	}
+	bpf_compute_data_end_sk_skb(skb);
+	if (tls_sw_has_ctx_rx(skb->sk)) {
+		struct strp_msg *rxm = strp_msg(skb);
+
+		rxm->full_len += len_diff;
+	}
+	return ret;
+}
+
+static const struct bpf_func_proto sk_skb_adjust_room_proto = {
+	.func		= sk_skb_adjust_room,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_ANYTHING,
+	.arg4_type	= ARG_ANYTHING,
+};
+
 BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff,
 	   u32, mode, u64, flags)
 {
@@ -6745,6 +6788,7 @@ bool bpf_helper_changes_pkt_data(void *func)
 	    func == bpf_skb_change_tail ||
 	    func == sk_skb_change_tail ||
 	    func == bpf_skb_adjust_room ||
+	    func == sk_skb_adjust_room ||
 	    func == bpf_skb_pull_data ||
 	    func == sk_skb_pull_data ||
 	    func == bpf_clone_redirect ||
@@ -7218,6 +7262,8 @@ sk_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &sk_skb_change_tail_proto;
 	case BPF_FUNC_skb_change_head:
 		return &sk_skb_change_head_proto;
+	case BPF_FUNC_skb_adjust_room:
+		return &sk_skb_adjust_room_proto;
 	case BPF_FUNC_get_socket_cookie:
 		return &bpf_get_socket_cookie_proto;
 	case BPF_FUNC_get_socket_uid:

tools/testing/selftests/bpf/progs/test_sockmap_kern.h

@@ -131,39 +131,55 @@ int bpf_prog2(struct __sk_buff *skb)
 
 }
 
-SEC("sk_skb3")
-int bpf_prog3(struct __sk_buff *skb)
+static inline void bpf_write_pass(struct __sk_buff *skb, int offset)
 {
-	const int one = 1;
-	int err, *f, ret = SK_PASS;
+	int err = bpf_skb_pull_data(skb, 6 + offset);
 	void *data_end;
 	char *c;
 
-	err = bpf_skb_pull_data(skb, 19);
 	if (err)
-		goto tls_out;
+		return;
 
 	c = (char *)(long)skb->data;
 	data_end = (void *)(long)skb->data_end;
 
-	if (c + 18 < data_end)
-		memcpy(&c[13], "PASS", 4);
+	if (c + 5 + offset < data_end)
+		memcpy(c + offset, "PASS", 4);
+}
+
+SEC("sk_skb3")
+int bpf_prog3(struct __sk_buff *skb)
+{
+	int err, *f, ret = SK_PASS;
+	const int one = 1;
+
 	f = bpf_map_lookup_elem(&sock_skb_opts, &one);
 	if (f && *f) {
 		__u64 flags = 0;
 
 		ret = 0;
 		flags = *f;
+
+		err = bpf_skb_adjust_room(skb, -13, 0, 0);
+		if (err)
+			return SK_DROP;
+		err = bpf_skb_adjust_room(skb, 4, 0, 0);
+		if (err)
+			return SK_DROP;
+		bpf_write_pass(skb, 0);
 #ifdef SOCKMAP
 		return bpf_sk_redirect_map(skb, &tls_sock_map, ret, flags);
 #else
 		return bpf_sk_redirect_hash(skb, &tls_sock_map, &ret, flags);
 #endif
 	}
-
 	f = bpf_map_lookup_elem(&sock_skb_opts, &one);
 	if (f && *f)
 		ret = SK_DROP;
+	err = bpf_skb_adjust_room(skb, 4, 0, 0);
+	if (err)
+		return SK_DROP;
+	bpf_write_pass(skb, 13);
 tls_out:
 	return ret;
 }

tools/testing/selftests/bpf/test_sockmap.c

@@ -518,28 +518,13 @@ static int msg_verify_data(struct msghdr *msg, int size, int chunk_sz)
 		if (i == 0 && txmsg_ktls_skb) {
 			if (msg->msg_iov[i].iov_len < 4)
 				return -EIO;
-			if (txmsg_ktls_skb_redir) {
-				if (memcmp(&d[13], "PASS", 4) != 0) {
-					fprintf(stderr,
-						"detected redirect ktls_skb data error with skb ingress update @iov[%i]:%i \"%02x %02x %02x %02x\" != \"PASS\"\n", i, 0, d[13], d[14], d[15], d[16]);
-					return -EIO;
-				}
-				d[13] = 0;
-				d[14] = 1;
-				d[15] = 2;
-				d[16] = 3;
-				j = 13;
-			} else if (txmsg_ktls_skb) {
 			if (memcmp(d, "PASS", 4) != 0) {
 				fprintf(stderr,
-						"detected ktls_skb data error with skb ingress update @iov[%i]:%i \"%02x %02x %02x %02x\" != \"PASS\"\n", i, 0, d[0], d[1], d[2], d[3]);
+					"detected skb data error with skb ingress update @iov[%i]:%i \"%02x %02x %02x %02x\" != \"PASS\"\n",
+					i, 0, d[0], d[1], d[2], d[3]);
 				return -EIO;
 			}
-				d[0] = 0;
-				d[1] = 1;
-				d[2] = 2;
-				d[3] = 3;
-			}
+			j = 4; /* advance index past PASS header */
 		}
 
 		for (; j < msg->msg_iov[i].iov_len && size; j++) {