commit c56cf8fe4742a3460d501a223d17ede6cbcde148 Author: Juhani Krekelä Date: Wed Jul 3 22:20:25 2019 +0300 First commit diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..7a01446 --- /dev/null +++ b/.gitignore @@ -0,0 +1,3 @@ +*.swp +*.o +ethertype-dump diff --git a/CC0 b/CC0 new file mode 100644 index 0000000..670154e --- /dev/null +++ b/CC0 @@ -0,0 +1,116 @@ +CC0 1.0 Universal + +Statement of Purpose + +The laws of most jurisdictions throughout the world automatically confer +exclusive Copyright and Related Rights (defined below) upon the creator and +subsequent owner(s) (each and all, an "owner") of an original work of +authorship and/or a database (each, a "Work"). + +Certain owners wish to permanently relinquish those rights to a Work for the +purpose of contributing to a commons of creative, cultural and scientific +works ("Commons") that the public can reliably and without fear of later +claims of infringement build upon, modify, incorporate in other works, reuse +and redistribute as freely as possible in any form whatsoever and for any +purposes, including without limitation commercial purposes. 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Affirmer understands and acknowledges that Creative Commons is not a + party to this document and has no duty or obligation with respect to this + CC0 or use of the Work. + +For more information, please see + diff --git a/Makefile b/Makefile new file mode 100644 index 0000000..948d040 --- /dev/null +++ b/Makefile @@ -0,0 +1,32 @@ +DESTDIR ?= +PREFIX ?= /usr/local +EXEC_PREFIX ?= $(PREFIX) +BINDIR ?= $(DESTDIR)$(EXEC_PREFIX)/bin + +CFLAGS += -Os -g -Wall -Wextra -pedantic +CPPFLAGS += +LDFLAGS += + +.SUFFIXES: +.SUFFIXES: .c .o + +.PHONY: all install uninstall clean distclean + +all: ethertype-dump + +ethertype-dump: ethertype-dump.o + $(CC) -o $@ $< $(LDFLAGS) + +.c.o: + $(CC) -c $(CFLAGS) $(CPPFLAGS) -o $@ $< + +install: all + install ethertype-dump $(BINDIR) + +uninstall: + rm $(BINDIR)/ethertype-dump + +clean: + rm -f ethertype-dump *.o + +distclean: clean diff --git a/ethertype-dump.c b/ethertype-dump.c new file mode 100644 index 0000000..0c6cd0d --- /dev/null +++ b/ethertype-dump.c @@ -0,0 +1,66 @@ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +int main(void) { + // Create a packet socket + errno = 0; + int packet_socket = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL)); + if (packet_socket == -1) { + err(1, "socket"); + } + + // Find the index of the network interface + struct ifreq ifr; + strncpy(ifr.ifr_name, "wlan0", IFNAMSIZ); + errno = 0; + if (ioctl(packet_socket, SIOCGIFINDEX, &ifr) == -1) { + err(1, "ioctl"); + } + + // Bind to the network interface + struct sockaddr_ll sll; + sll.sll_family = AF_PACKET; + sll.sll_protocol = htons(ETH_P_ALL); + sll.sll_ifindex = ifr.ifr_ifindex; + errno = 0; + if (bind(packet_socket, (const struct sockaddr*)&sll, sizeof(sll)) == -1) { + err(1, "bind"); + } + + for(;;) { + char frame[1522]; // 1522 is the largest a 802.3 frame can be + + errno = 0; + ssize_t frame_length = recv(packet_socket, frame, sizeof(frame), MSG_TRUNC); + if (frame_length == -1) { + err(1, "recv"); + } + + // Extract EtherType / length field + // 012345 012345 01 + // dest source ^^ + // It is stored in the network byte order, that is, high byte 1st + if (frame_length < 14) { + errx(1, "Very weird frame of only %zdB???", frame_length); + } + uint16_t ethertype_length = (frame[12] << 8) | frame[13]; + + errno = 0; + if(printf("ethertype: %02x%02x, length: %zd\n", ethertype_length >> 8, ethertype_length & 0xff, frame_length) == -1) { + err(1, "printf"); + } + } + + return 0; +}