From 257259dd79d103f23342b1f0a3d608571a0ad549 Mon Sep 17 00:00:00 2001
From: Roy Marples <roy@marples.name>
Date: Thu, 13 Apr 2023 17:43:11 +0100
Subject: [PATCH] bpf: Always open /dev/bpf directly

Ignore _PATH_BPF as that's really a NetBSDism.
If /dev/bpf throws a wobbly then try /dev/bpfN for older kernels.

This allows cloning BPF on more BSD systems.
---
 src/bpf.c | 36 +++++++++++++++++-------------------
 1 file changed, 17 insertions(+), 19 deletions(-)

diff --git a/src/bpf.c b/src/bpf.c
index e4b56f3d..b75bfb04 100644
--- a/src/bpf.c
+++ b/src/bpf.c
@@ -45,7 +45,6 @@
 
 #include <errno.h>
 #include <fcntl.h>
-#include <paths.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
@@ -155,6 +154,11 @@ bpf_open(const struct interface *ifp,
 	struct bpf_version pv = { .bv_major = 0, .bv_minor = 0 };
 	struct ifreq ifr = { .ifr_flags = 0 };
 	int ibuf_len = 0;
+#ifdef O_CLOEXEC
+#define BPF_OPEN_FLAGS O_RDWR | O_NONBLOCK | O_CLOEXEC
+#else
+#define BPF_OPEN_FLAGS O_RDWR | O_NONBLOCK
+#endif
 #ifdef BIOCIMMEDIATE
 	unsigned int flags;
 #endif
@@ -167,25 +171,19 @@ bpf_open(const struct interface *ifp,
 		return NULL;
 	bpf->bpf_ifp = ifp;
 
-#ifdef _PATH_BPF
-	bpf->bpf_fd = open(_PATH_BPF, O_RDWR | O_NONBLOCK
-#ifdef O_CLOEXEC
-		| O_CLOEXEC
-#endif
-	);
-#else
-	char device[32];
-	int n = 0;
+	/* /dev/bpf is a cloner on modern kernels */
+	bpf->bpf_fd = open("/dev/bpf", BPF_OPEN_FLAGS);
 
-	do {
-		snprintf(device, sizeof(device), "/dev/bpf%d", n++);
-		bpf->bpf_fd = open(device, O_RDWR | O_NONBLOCK
-#ifdef O_CLOEXEC
-				| O_CLOEXEC
-#endif
-		);
-	} while (bpf->bpf_fd == -1 && errno == EBUSY);
-#endif
+	/* Support older kernels where /dev/bpf is not a cloner */
+	if (bpf->bpf_fd == -1) {
+		char device[32];
+		int n = 0;
+
+		do {
+			snprintf(device, sizeof(device), "/dev/bpf%d", n++);
+			bpf->bpf_fd = open(device, BPF_OPEN_FLAGS);
+		} while (bpf->bpf_fd == -1 && errno == EBUSY);
+	}
 
 	if (bpf->bpf_fd == -1)
 		goto eexit;