copypaste: simple program that just copies a file

Supports "zero-copy" copying on Linux, but copying with low ram and on FreeBSD the program itself wasn't tested.

copypaste.c

@@ -0,0 +1,175 @@
+/***************************************************
+* 
+* Name: copypaste
+* Description: Utility for copying and pasting files
+* Author: 000exploit
+* Purpose: Exploring the possibilities of read() and
+* 	   write() syscalls as tool for duplicating
+* 	   information.
+*
+***************************************************/
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/statvfs.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+
+/*
+* EXIT CODE CONVENTION
+* 0 - success
+* 1 - params error
+* 2 - I/O error
+*/
+
+const char helpmsg[] = "Usage:\n\tcopypaste [src] [dest]";
+
+int bufrw(int inputfd, int outputfd, char* buf, int size) {
+	int readval = read(inputfd, buf, size);
+	if (readval < 0) {
+ioerr:		perror("I/O error");
+		return 2;
+	} else if (readval == 0) {
+		perror("Unexpected EOF");
+		return 2;
+	}
+
+	int writeval = write(outputfd, buf, size);
+	if (writeval < 0) {
+		goto ioerr;
+	}
+	return 0;
+}
+
+int copyfile(char* src, char* dest)
+{
+	int srcfd = open(src, O_RDONLY);
+	int destfd = open(dest, O_CREAT | O_WRONLY | O_TRUNC, S_IRWXU);
+
+	if (!srcfd) {
+		fprintf(stderr, "Failed to open \"%s\".", src);
+		return 1;
+	}
+	if (!destfd) {
+		fprintf(stderr, "Failed to open \"%s\".", dest);
+		return 1;
+	}
+
+	struct stat srcstat = {0};
+	int statret = fstat(srcfd, &srcstat);
+	if (statret < 0)
+		return 2;
+
+	printf("File size: %li bytes\n", srcstat.st_size);
+
+	int wstatus = 0;
+	int pid = fork();
+	if (pid == 0) {
+#ifdef __unix__
+		struct statvfs fsstat = {0};
+		if ((fstatvfs(destfd, &fsstat)) == 0) {
+			if (fsstat.f_bavail < srcstat.st_size) {
+				fprintf(stderr,\
+					"Insufficient disk space. Requested: %li, available: %li\n",\
+					srcstat.st_size, fsstat.f_bavail);
+				return 2;
+			}
+		}
+#if defined(__linux__) && defined(ZEROCOPYV1)
+#include <sys/sendfile.h>
+		int sendval = sendfile(destfd, srcfd, 0, srcstat.st_size);
+		if (sendval < 0) {
+			perror("I/O error");
+			return 2;
+		}
+		fprintf(stderr, "Total write: %i bytes\n", sendval);
+#else
+		int page_size = sysconf(_SC_PAGE_SIZE);
+		int avail_pages = -1;
+#ifdef __linux__
+		avail_pages = sysconf(_SC_AVPHYS_PAGES);
+
+#elif __freebsd__
+#include <sys/sysctl.h>
+		int sysctlreq[2] = {CTL_HW, HW_AVAILPAGES};
+		size_t len = sizeof(sysctlreq);
+		int sysctlret = sysctl(sysctlreq, 2, &avail_pages, &len, NULL, 0);
+		if (sysctlreq < 0) {
+			perror("sysctl");
+			avail_pages = -1;
+		}
+#endif
+		char* buf;
+		unsigned long free_memory = 0;
+		if (avail_pages != -1) {
+			free_memory = page_size * avail_pages;
+			if (free_memory < (unsigned long)(srcstat.st_size - LONG_MAX))
+				buf = malloc(free_memory);
+		} else {
+				buf = malloc(sizeof(char)*srcstat.st_size);
+				free_memory = 0;
+		}
+		if (buf == NULL) {
+			perror("Critical error");
+			return 2;
+		}
+
+		if (!free_memory) {
+			int tail = srcstat.st_size % free_memory;
+			int total = (srcstat.st_size - tail) / free_memory;
+
+			for (int i = 0; i < total; i++) {
+				int bufrwret = bufrw(srcfd, destfd, buf, total);
+				if (bufrwret != 0)
+					return 2;
+			}
+			if (tail > 0) {
+				bufrw(srcfd, destfd, buf, tail);
+			}
+		} else {
+			int bufrwret = bufrw(srcfd, destfd, buf, srcstat.st_size);
+			if (bufrwret != 0)
+				return 2;
+		}
+
+		free(buf);
+#endif
+#else
+#error "Only UNIX-like systems is supported."
+#endif
+		exit(0);
+	}
+	waitpid(0, &wstatus, 0);
+	close(srcfd);
+	close(destfd);
+	if (WIFEXITED(wstatus))
+		return 2;
+
+	return 0;
+}
+
+int main(int argc, char* argv[])
+{
+	if (argc < 3) {
+		printf("%s\n", helpmsg);
+		return 1;
+	}
+
+	int src = access(argv[1], F_OK | R_OK);
+	//int dest = access(argv[2], W_OK);
+	if (src != 0)
+	{
+		fputs("Invalid source file path.\n", stdout);
+		return 1;
+	}
+
+	int ret = copyfile(argv[1], argv[2]);
+
+	return ret;
+}