File Access Monitor

accessmonitor

#!/bin/sh

PROGRAM="$1"
shift
LD_PRELOAD="$HOME/local/lib/accessmonitor.so" exec "$PROGRAM" "$@"

accessmonitor.c

#define _GNU_SOURCE 1
#include <dlfcn.h>
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <fcntl.h>

FILE* fopen(const char* path, const char* mode)
{
    FILE* (*orig)(const char*, const char*) = dlsym(RTLD_NEXT, "fopen");
    fprintf(stderr, "%-70s %s\n", path, mode);
    return orig(path, mode);
}

int open(const char* filename, int flags, ...)
{
    int (*orig)(const char*, int, ...) = (int(*)(const char*, int, ...))dlsym(RTLD_NEXT, "open");
    if (flags & O_CREAT) {
        va_list ap;
        int mode;

        va_start(ap, flags);
        mode = va_arg(ap, mode_t);
        va_end(ap);

        if (strcmp(filename, ".")) {
            fprintf(stderr, "%-70s %4d %4d\n", filename, flags, mode);
        }

        return orig(filename, flags, mode);
    } else {
        if (strcmp(filename, ".")) {
            fprintf(stderr, "%-70s %4d\n", filename, flags);
        }
        return orig(filename, flags);
    }
}

int open64(const char* filename, int flags, ...)
{
    int (*orig)(const char*, int, ...) = (int(*)(const char*, int, ...))dlsym(RTLD_NEXT, "open64");
    if (flags & O_CREAT) {
        va_list ap;
        int mode;

        va_start(ap, flags);
        mode = va_arg(ap, mode_t);
        va_end(ap);

        if (strcmp(filename, ".")) {
            fprintf(stderr, "%-70s %4d %4d\n", filename, flags, mode);
        }

        return orig(filename, flags, mode);
    } else {
        if (strcmp(filename, ".")) {
            fprintf(stderr, "%-70s %4d\n", filename, flags);
        }
        return orig(filename, flags);
    }
}

Makefile

CFLAGS=-O2 -Wall -Wextra

.PHONY: all
all: accessmonitor.so

accessmonitor.so: accessmonitor.c
	$(CC) $(CFLAGS) -fPIC -shared -ldl $< -o $@