open a non-existent interface should always return 'no such interface'

Signed-off-by: Afshin Paydar <[email protected]>

Author: Afshin Paydar

pcap-bpf.c

@@ -626,6 +626,58 @@ bpf_open(char *errbuf)
 #define BPF_BIND_SUCCEEDED	0
 #define BPF_BIND_BUFFER_TOO_BIG	1
 
+/*
+ * Check if an interface exists without requiring special privileges.
+ * Returns 0 if the interface exists, PCAP_ERROR_NO_SUCH_DEVICE if it doesn't,
+ * or another negative error code on other failures.
+ */
+static int
+check_interface_exists(const char *name, char *errbuf)
+{
+#ifndef _WIN32
+	int fd;
+	struct ifreq ifr;
+
+	if (strlen(name) >= sizeof(ifr.ifr_name)) {
+		/* The name is too long, so it can't possibly exist. */
+		errbuf[0] = '\0';
+		return PCAP_ERROR_NO_SUCH_DEVICE;
+	}
+
+	fd = socket(AF_INET, SOCK_DGRAM, 0);
+	if (fd < 0) {
+		pcapint_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
+		    errno, "socket");
+		return PCAP_ERROR;
+	}
+
+	memset(&ifr, 0, sizeof(ifr));
+	pcapint_strlcpy(ifr.ifr_name, name, sizeof(ifr.ifr_name));
+
+	if (ioctl(fd, SIOCGIFFLAGS, &ifr) < 0) {
+		int save_errno = errno;
+		close(fd);
+
+		if (save_errno == ENXIO || save_errno == ENODEV) {
+			/* Interface doesn't exist */
+			errbuf[0] = '\0';
+			return PCAP_ERROR_NO_SUCH_DEVICE;
+		} else {
+			/* Some other error occurred */
+			pcapint_fmt_errmsg_for_errno(errbuf, PCAP_ERRBUF_SIZE,
+			    save_errno, "SIOCGIFFLAGS on %s", name);
+			return PCAP_ERROR;
+		}
+	}
+
+	close(fd);
+	return 0;
+#else
+	/* On Windows, skip the check for now */
+	return 0;
+#endif
+}
+
 static int
 bpf_bind(int fd, const char *name, char *errbuf)
 {
@@ -1923,6 +1975,16 @@ pcap_activate_bpf(pcap_t *p)
 	int flags = MAP_ANON;
 #endif
 
+	/*
+	 * Check if the interface exists before trying to open BPF device.
+	 * This avoids reporting permission errors when the real issue is
+	 * that the interface doesn't exist.
+	 */
+	status = check_interface_exists(p->opt.device, p->errbuf);
+	if (status != 0) {
+		goto bad;
+	}
+
 	fd = bpf_open(p->errbuf);
 	if (fd < 0) {
 		status = fd;

pcap-linux.c

@@ -5164,13 +5164,13 @@ iface_get_ts_types(const char *device, pcap_t *handle, char *ebuf)
 
 		case ENODEV:
 			/*
-			 * OK, no such device.
-			 * The user will find that out when they try to
-			 * activate the device; just return an empty
-			 * list of time stamp types.
+			 * No such device.
+			 *
+			 * There's nothing more to say, so clear the
+			 * error message.
 			 */
-			handle->tstamp_type_list = NULL;
-			return 0;
+			ebuf[0] = '\0';
+			return PCAP_ERROR_NO_SUCH_DEVICE;
 
 		default:
 			/*