/*
* Unix implementation of SSH connection-sharing IPC setup.
*/
#include <stdio.h>
#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/file.h>
#include "tree234.h"
#include "putty.h"
#include "network.h"
#include "proxy/proxy.h"
#include "ssh.h"
#define CONNSHARE_SOCKETDIR_PREFIX "/tmp/putty-connshare"
#define SALT_FILENAME "salt"
#define SALT_SIZE 64
#ifndef PIPE_BUF
#define PIPE_BUF _POSIX_PIPE_BUF
#endif
static char *make_parentdir_name(void)
{
char *username, *parent;
username = get_username();
parent = dupprintf("%s.%s", CONNSHARE_SOCKETDIR_PREFIX, username);
sfree(username);
assert(*parent == '/');
return parent;
}
static char *make_dirname(const char *pi_name, char **logtext)
{
char *name, *parentdirname, *dirname, *err;
/*
* First, create the top-level directory for all shared PuTTY
* connections owned by this user.
*/
parentdirname = make_parentdir_name();
if ((err = make_dir_and_check_ours(parentdirname)) != NULL) {
*logtext = err;
sfree(parentdirname);
return NULL;
}
/*
* Transform the platform-independent version of the connection
* identifier into the name we'll actually use for the directory
* containing the Unix socket.
*
* We do this by hashing the identifier with some user-specific
* secret information, to avoid the privacy leak of having
* "user@host" strings show up in 'netstat -x'. (Irritatingly, the
* full pathname of a Unix-domain socket _does_ show up in the
* 'netstat -x' output, at least on Linux, even if that socket is
* in a directory not readable to the user running netstat. You'd
* think putting things inside an 0700 directory would hide their
* names from other users, but no.)
*
* The secret information we use to salt the hash lives in a file
* inside the top-level directory we just created, so we must
* first create that file (with some fresh random data in it) if
* it's not already been done by a previous PuTTY.
*/
{
unsigned char saltbuf[SALT_SIZE];
char *saltname;
int saltfd, i, ret;
saltname = dupprintf("%s/%s", parentdirname, SALT_FILENAME);
saltfd = open(saltname, O_RDONLY);
if (saltfd < 0) {
char *tmpname;
int pid;
if (errno != ENOENT) {
*logtext = dupprintf("%s: open: %s", saltname,
strerror(errno));
sfree(saltname);
sfree(parentdirname);
return NULL;
}
/*
* The salt file doesn't already exist, so try to create
* it. Another process may be attempting the same thing
* simultaneously, so we must do this carefully: we write
* a salt file under a different name, then hard-link it
* into place, which guarantees that we won't change the
* contents of an existing salt file.
*/
pid = getpid();
for (i = 0;; i++) {
tmpname = dupprintf("%s/%s.tmp.%d.%d",
parentdirname, SALT_FILENAME, pid, i);
saltfd = open(tmpname, O_WRONLY | O_EXCL | O_CREAT, 0400);
if (saltfd >= 0)
break;
if (errno != EEXIST) {
*logtext = dupprintf("%s: open: %s", tmpname,
strerror(errno));
sfree(tmpname);
sfree(saltname);
sfree(parentdirname);
return NULL;
}
sfree(tmpname); /* go round and try again with i+1 */
}
/*
* Invent some random data.
*/
random_read(saltbuf, SALT_SIZE);
ret = write(saltfd, saltbuf, SALT_SIZE);
/* POSIX atomicity guarantee: because we wrote less than
* PIPE_BUF bytes, the write either completed in full or
* failed. */
assert(SALT_SIZE < PIPE_BUF);
assert(ret < 0 || ret == SALT_SIZE);
if (ret < 0) {
close(saltfd);
*logtext = dupprintf("%s: write: %s", tmpname,
strerror(errno));
sfree(tmpname);
sfree(saltname);
sfree(parentdirname);
return NULL;
}
if (close(saltfd) < 0) {
*logtext = dupprintf("%s: close: %s", tmpname,
strerror(errno));
sfree(tmpname);
sfree(saltname);
sfree(parentdirname);
return NULL;
}
/*
* Now attempt to hard-link our temp file into place. We
* tolerate EEXIST as an outcome, because that just means
* another PuTTY got their attempt in before we did (and
* we only care that there is a valid salt file we can
* agree on, no matter who created it).
*/
if (link(tmpname, saltname) < 0 && errno != EEXIST) {
*logtext = dupprintf("%s: link: %s", saltname,
strerror(errno));
sfree(tmpname);
sfree(saltname);
sfree(parentdirname);
return NULL;
}
/*
* Whether that succeeded or not, get rid of our temp file.
*/
if (unlink(tmpname) < 0) {
*logtext = dupprintf("%s: unlink: %s", tmpname,
strerror(errno));
sfree(tmpname);
sfree(saltname);
sfree(parentdirname);
return NULL;
}
/*
* And now we've arranged for there to be a salt file, so
* we can try to open it for reading again and this time
* expect it to work.
*/
sfree(tmpname);
saltfd = open(saltname, O_RDONLY);
if (saltfd < 0) {
*logtext = dupprintf("%s: open: %s", saltname,
strerror(errno));
sfree(saltname);
sfree(parentdirname);
return NULL;
}
}
for (i = 0; i < SALT_SIZE; i++) {
ret = read(saltfd, saltbuf, SALT_SIZE);
if (ret <= 0) {
close(saltfd);
*logtext = dupprintf("%s: read: %s", saltname,
ret == 0 ? "unexpected EOF" :
strerror(errno));
sfree(saltname);
sfree(parentdirname);
return NULL;
}
assert(0 < ret && ret <= SALT_SIZE - i);
i += ret;
}
close(saltfd);
sfree(saltname);
/*
* Now we've got our salt, hash it with the connection
* identifier to produce our actual socket name.
*/
{
unsigned char digest[32];
char retbuf[65];
ssh_hash *h = ssh_hash_new(&ssh_sha256);
put_string(h, saltbuf, SALT_SIZE);
put_stringz(h, pi_name);
ssh_hash_final(h, digest);
/*
* And make it printable.
*/
for (i = 0; i < 32; i++) {
sprintf(retbuf + 2*i, "%02x", digest[i]);
/* the last of those will also write the trailing NUL */
}
name = dupstr(retbuf);
}
smemclr(saltbuf, sizeof(saltbuf));
}
dirname = dupprintf("%s/%s", parentdirname, name);
sfree(parentdirname);
sfree(name);
return dirname;
}
int platform_ssh_share(const char *pi_name, Conf *conf,
Plug *downplug, Plug *upplug, Socket **sock,
char **logtext, char **ds_err, char **us_err,
bool can_upstream, bool can_downstream)
{
char *dirname, *lockname, *sockname, *err;
int lockfd;
Socket *retsock;
/*
* Sort out what we're going to call the directory in which we
* keep the socket. This has the side effect of potentially
* creating its top-level containing dir and/or the salt file
* within that, if they don't already exist.
*/
dirname = make_dirname(pi_name, logtext);
if (!dirname) {
return SHARE_NONE;
}
/*
* Now make sure the subdirectory exists.
*/
if ((err = make_dir_and_check_ours(dirname)) != NULL) {
*logtext = err;
sfree(dirname);
return SHARE_NONE;
}
/*
* Acquire a lock on a file in that directory.
*/
lockname = dupcat(dirname, "/lock");
lockfd = open(lockname, O_CREAT | O_RDWR | O_TRUNC, 0600);
if (lockfd < 0) {
*logtext = dupprintf("%s: open: %s", lockname, strerror(errno));
sfree(dirname);
sfree(lockname);
return SHARE_NONE;
}
if (flock(lockfd, LOCK_EX) < 0) {
*logtext = dupprintf("%s: flock(LOCK_EX): %s",
lockname, strerror(errno));
sfree(dirname);
sfree(lockname);
close(lockfd);
return SHARE_NONE;
}
sockname = dupprintf("%s/socket", dirname);
*logtext = NULL;
if (can_downstream) {
retsock = new_connection(unix_sock_addr(sockname),
"", 0, false, true, false, false,
downplug, conf, NULL);
if (sk_socket_error(retsock) == NULL) {
sfree(*logtext);
*logtext = sockname;
*sock = retsock;
sfree(dirname);
sfree(lockname);
close(lockfd);
return SHARE_DOWNSTREAM;
}
sfree(*ds_err);
*ds_err = dupprintf("%s: %s", sockname, sk_socket_error(retsock));
sk_close(retsock);
}
if (can_upstream) {
retsock = new_unix_listener(unix_sock_addr(sockname), upplug);
if (sk_socket_error(retsock) == NULL) {
sfree(*logtext);
*logtext = sockname;
*sock = retsock;
sfree(dirname);
sfree(lockname);
close(lockfd);
return SHARE_UPSTREAM;
}
sfree(*us_err);
*us_err = dupprintf("%s: %s", sockname, sk_socket_error(retsock));
sk_close(retsock);
}
/* One of the above clauses ought to have happened. */
assert(*logtext || *ds_err || *us_err);
sfree(dirname);
sfree(lockname);
sfree(sockname);
close(lockfd);
return SHARE_NONE;
}
void platform_ssh_share_cleanup(const char *name)
{
char *dirname, *filename, *logtext;
dirname = make_dirname(name, &logtext);
if (!dirname) {
sfree(logtext); /* we can't do much with this */
return;
}
filename = dupcat(dirname, "/socket");
remove(filename);
sfree(filename);
filename = dupcat(dirname, "/lock");
remove(filename);
sfree(filename);
rmdir(dirname);
/*
* We deliberately _don't_ clean up the parent directory
* /tmp/putty-connshare.<username>, because if we leave it around
* then it reduces the ability for other users to be a nuisance by
* putting their own directory in the way of it. Also, the salt
* file in it can be reused.
*/
sfree(dirname);
}