Add to if_enc(4) ability to capture packets via BPF after pfil processing.

New flag 0x4 can be configured in net.enc.[in|out].ipsec_bpf_mask.
When it is set, if_enc(4) additionally captures a packet via BPF after
invoking pfil hook. This may be useful for debugging.

MFC after:	2 weeks
Sponsored by:	Yandex LLC
Differential Revision:	https://reviews.freebsd.org/D11804

share/man/man4/enc.4

@@ -31,7 +31,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 28, 2007
+.Dd August 9, 2017
 .Dt ENC 4
 .Os
 .Sh NAME
@@ -44,6 +44,13 @@ kernel configuration file:
 .Bd -ragged -offset indent
 .Cd "device enc"
 .Ed
+.Pp
+Alternatively, to load the driver as a
+module at boot time, place the following line in
+.Xr loader.conf 5 :
+.Bd -literal -offset indent
+if_enc_load="YES"
+.Ed
 .Sh DESCRIPTION
 The
 .Nm
@@ -115,6 +122,11 @@ outgoing path                                          |------|
 Most people will want to run with the suggested defaults for
 .Cm ipsec_filter_mask
 and rely on the security policy database for the outer headers.
+.Pp
+Note that packets are captured by BPF before firewall processing.
+The special value 0x4 can be configured in the
+.Ar ipsec_bpf_mask
+and packets will be also captured after firewall processing.
 .Sh EXAMPLES
 To see the packets the processed via
 .Xr ipsec 4 ,

sys/net/if_enc.c

@@ -99,9 +99,15 @@ static void	enc_remove_hhooks(struct enc_softc *);
 
 static const char encname[] = "enc";
 
+#define	IPSEC_ENC_AFTER_PFIL	0x04
 /*
  * Before and after are relative to when we are stripping the
  * outer IP header.
+ *
+ * AFTER_PFIL flag used only for bpf_mask_*. It enables BPF capturing
+ * after PFIL hook execution. It might be useful when PFIL hook does
+ * some changes to the packet, e.g. address translation. If PFIL hook
+ * consumes mbuf, nothing will be captured.
  */
 static VNET_DEFINE(int, filter_mask_in) = IPSEC_ENC_BEFORE;
 static VNET_DEFINE(int, bpf_mask_in) = IPSEC_ENC_BEFORE;
@@ -194,6 +200,30 @@ enc_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 	return (0);
 }
 
+static void
+enc_bpftap(struct ifnet *ifp, struct mbuf *m, const struct secasvar *sav,
+    int32_t hhook_type, uint8_t enc, uint8_t af)
+{
+	struct enchdr hdr;
+
+	if (hhook_type == HHOOK_TYPE_IPSEC_IN &&
+	    (enc & V_bpf_mask_in) == 0)
+		return;
+	else if (hhook_type == HHOOK_TYPE_IPSEC_OUT &&
+	    (enc & V_bpf_mask_out) == 0)
+		return;
+	if (bpf_peers_present(ifp->if_bpf) == 0)
+		return;
+	hdr.af = af;
+	hdr.spi = sav->spi;
+	hdr.flags = 0;
+	if (sav->alg_enc != SADB_EALG_NONE)
+		hdr.flags |= M_CONF;
+	if (sav->alg_auth != SADB_AALG_NONE)
+		hdr.flags |= M_AUTH;
+	bpf_mtap2(ifp->if_bpf, &hdr, sizeof(hdr), m);
+}
+
 /*
  * One helper hook function is used by any hook points.
  * + from hhook_type we can determine the packet direction:
@@ -206,7 +236,6 @@ static int
 enc_hhook(int32_t hhook_type, int32_t hhook_id, void *udata, void *ctx_data,
     void *hdata, struct osd *hosd)
 {
-	struct enchdr hdr;
 	struct ipsec_ctx_data *ctx;
 	struct enc_softc *sc;
 	struct ifnet *ifp, *rcvif;
@@ -223,21 +252,7 @@ enc_hhook(int32_t hhook_type, int32_t hhook_id, void *udata, void *ctx_data,
 	if (ctx->af != hhook_id)
 		return (EPFNOSUPPORT);
 
-	if (((hhook_type == HHOOK_TYPE_IPSEC_IN &&
+	enc_bpftap(ifp, *ctx->mp, ctx->sav, hhook_type, ctx->enc, ctx->af);
-	    (ctx->enc & V_bpf_mask_in) != 0) ||
-	    (hhook_type == HHOOK_TYPE_IPSEC_OUT &&
-	    (ctx->enc & V_bpf_mask_out) != 0)) &&
-	    bpf_peers_present(ifp->if_bpf) != 0) {
-		hdr.af = ctx->af;
-		hdr.spi = ctx->sav->spi;
-		hdr.flags = 0;
-		if (ctx->sav->alg_enc != SADB_EALG_NONE)
-			hdr.flags |= M_CONF;
-		if (ctx->sav->alg_auth != SADB_AALG_NONE)
-			hdr.flags |= M_AUTH;
-		bpf_mtap2(ifp->if_bpf, &hdr, sizeof(hdr), *ctx->mp);
-	}
-
 	switch (hhook_type) {
 	case HHOOK_TYPE_IPSEC_IN:
 		if (ctx->enc == IPSEC_ENC_BEFORE) {
@@ -290,6 +305,8 @@ enc_hhook(int32_t hhook_type, int32_t hhook_id, void *udata, void *ctx_data,
 		return (EACCES);
 	}
 	(*ctx->mp)->m_pkthdr.rcvif = rcvif;
+	enc_bpftap(ifp, *ctx->mp, ctx->sav, hhook_type,
+	    IPSEC_ENC_AFTER_PFIL, ctx->af);
 	return (0);
 }