1 |
NAME |
2 |
libptytty - OS independent and secure pty/tty and utmp/wtmp/lastlog |
3 |
handling |
4 |
|
5 |
SYNOPSIS |
6 |
cc ... -lptytty |
7 |
|
8 |
#include <libptytty.h> |
9 |
|
10 |
// C++ |
11 |
ptytty *pty = ptytty::create (); |
12 |
|
13 |
if (!pty->get ()) |
14 |
// error allocating pty |
15 |
|
16 |
if (we want utmp) |
17 |
pty->login (process_pid, 0, "remote.host"); |
18 |
else if (we want utmp AND wtmp/lastlog) |
19 |
pty->login (process_pid, 1, "remote.host"); |
20 |
|
21 |
// we are done with it |
22 |
delete pty; |
23 |
|
24 |
// C |
25 |
PTYTTY pty = ptytty_create (); |
26 |
|
27 |
if (!ptytty_get (pty)) |
28 |
// error allocating pty |
29 |
|
30 |
if (we want utmp) |
31 |
ptytty_login (pty, process_pid, 0, "remote.host"); |
32 |
else if (we want utmp AND wtmp/lastlog) |
33 |
ptytty_login (pty, process_pid, 1, "remote.host"); |
34 |
|
35 |
// we are done with it |
36 |
ptytty_delete (pty); |
37 |
|
38 |
See also the eg/ directory, which currently contains the c-sample.c file |
39 |
that spawns a loginshell from C using libptytty. |
40 |
|
41 |
DESCRIPTION |
42 |
Libptytty is a small library that offers pseudo-tty management in an |
43 |
OS-independent way. It was created out of frustration over the many |
44 |
differences of pty/tty handling in different operating systems for the |
45 |
use inside "rxvt-unicode". |
46 |
|
47 |
In addition to offering mere pty/tty management, it also offers session |
48 |
database support (utmp and optional wtmp/lastlog updates for login |
49 |
shells). |
50 |
|
51 |
It also supports fork'ing after startup and dropping privileges in the |
52 |
calling process, so in case the calling process gets compromised by the |
53 |
user starting the program there is less to gain, as only the helper |
54 |
process runs with privileges (e.g. setuid/setgid), which reduces the |
55 |
area of attack immensely. |
56 |
|
57 |
Libptytty is written in C++, but it also offers a C-only API. |
58 |
|
59 |
SECURITY CONSIDERATIONS |
60 |
*It is of paramount importance that you at least read the following |
61 |
paragraph!* |
62 |
|
63 |
If you are a typical terminal-like program that just wants one or more |
64 |
ptys, you should call the "ptytty::init ()" method (C: "ptytty_init ()" |
65 |
function) as the very first thing in your program: |
66 |
|
67 |
int main (int argc, char *argv[]) |
68 |
{ |
69 |
// do nothing here |
70 |
ptytty::init (); |
71 |
// in C: ptytty_init (); |
72 |
|
73 |
// initialise, parse arguments, etc. |
74 |
} |
75 |
|
76 |
This checks wether the program runs setuid or setgid. If yes then it |
77 |
will fork a helper process and drop privileges. |
78 |
|
79 |
Some programs need finer control over if and when this helper process is |
80 |
started, and if and how to drop privileges. For those programs, the |
81 |
methods "ptytty::use_helper" and "ptytty::drop_privileges" are more |
82 |
useful. |
83 |
|
84 |
C++ INTERFACE: THE ptytty CLASS |
85 |
STATIC METHODS |
86 |
ptytty::init () |
87 |
The default way to initialise libptytty. Must be called imemdiately |
88 |
as the first thing in the "main" function, or earlier e.g. during |
89 |
static construction time. The earlier, the better. |
90 |
|
91 |
This method checks wether the program runs with setuid/setgid |
92 |
permissions and, if yes, spawns a helper process for pty/tty |
93 |
management. It then drops the privileges completely, so the actual |
94 |
program runs without setuid/setgid privileges. |
95 |
|
96 |
ptytty::use_helper () |
97 |
Tries to start a helper process that retains privileges even when |
98 |
the calling process does not. This is usually called from |
99 |
"ptytty::init" when it detects that the program is running setuid or |
100 |
setgid, but can be called manually if it is inconvinient to drop |
101 |
privileges at startup, or when you are not running setuid/setgid but |
102 |
want to drop privileges (e.g. when running as a root-started |
103 |
daemon). |
104 |
|
105 |
This method will try not to start more than one helper process. The |
106 |
same helper process can usually be used both from the process |
107 |
starting it and all its fork'ed (not exec'ed) children. |
108 |
|
109 |
ptytty::drop_privileges () |
110 |
Drops privileges completely, i.e. sets real, effective and saved |
111 |
user id to the real user id. Also aborts if this cannot be achieved. |
112 |
Useful to make sure that the process doesn't run with special |
113 |
privileges. |
114 |
|
115 |
bool success = ptytty::send_fd (int socket, int fd) |
116 |
Utility method to send a file descriptor over a unix domain socket. |
117 |
Returns true if successful, false otherwise. This method is only |
118 |
exposed for your convinience and is not required for normal |
119 |
operation. |
120 |
|
121 |
int fd = ptytty::recv_fd (int socket) |
122 |
Utility method to receive a file descriptor over a unix domain |
123 |
socket. Returns the fd if sucecssful and -1 otherwise. This method |
124 |
is only exposed for your convinience and is not required for normal |
125 |
operation. |
126 |
|
127 |
ptytty *pty = ptytty::create () |
128 |
Creates new ptytty object. Creation does not yet do anything besides |
129 |
allocating the structure. |
130 |
|
131 |
A static method is used because the actual ptytty implementation can |
132 |
differ at runtime, so you need a dynamic object creation facility. |
133 |
|
134 |
DYNAMIC/SESSION-RELATED DATA MEMBERS AND METHODS |
135 |
int pty_fd = pty->pty |
136 |
int tty_fd = pty->tty |
137 |
These members contain the pty and tty file descriptors, |
138 |
respectively. They initially contain -1 until a successful to |
139 |
"ptytty::get". |
140 |
|
141 |
bool success = pty->get () |
142 |
Tries to find, allocate and initialise a new pty/tty pair. Returns |
143 |
"true" when successful. |
144 |
|
145 |
pty->login (int cmd_pid, bool login_shell, const char *hostname) |
146 |
Creates an entry in the systems session database(s) (utmp, wtmp, |
147 |
lastlog). "cmd_pid" must be the pid of the process representing the |
148 |
session (such as the login shell), "login_shell" defines wether the |
149 |
session is associated with a login, which influences wether wtmp and |
150 |
lastlog entries are created, and "hostname" should identify the |
151 |
"hostname" the user logs in from, which often is the value of the |
152 |
"DISPLAY" variable or tty line in case of local logins. |
153 |
|
154 |
Calling this method is optional. A session starts at the time of the |
155 |
login call and extends until the ptytty object is destroyed. |
156 |
|
157 |
pty->close_tty () |
158 |
Closes the tty. Useful after forking in the parent/pty process. |
159 |
|
160 |
bool success = pty->make_controlling_tty () |
161 |
Tries to make the pty/tty pair the controlling terminal of the |
162 |
current process. Useful after forking in the child/tty process. |
163 |
|
164 |
pty->set_utf8_mode (bool on) |
165 |
On systems supporting special UTF-8 line disciplines (e.g. Linux), |
166 |
this tries to enable this discipline for the given pty. Can be |
167 |
called at any time to change the mode. |
168 |
|
169 |
C INTERFACE: THE ptytty FAMILY OF FUNCTIONS |
170 |
ptytty_init () |
171 |
See "ptytty::init ()". |
172 |
|
173 |
PTYTTY ptytty_create () |
174 |
Creates a new opaque PTYTTY object and returns it. Do not try to |
175 |
access it in any way except by testing it for truthness (e.g. "if |
176 |
(pty) ...."). See "ptytty::create ()". |
177 |
|
178 |
int ptytty_pty (PTYTTY ptytty) |
179 |
Return the pty file descriptor. See "pty->pty". |
180 |
|
181 |
int ptytty_tty (PTYTTY ptytty) |
182 |
Return the tty file descriptor. See "pty->tty". |
183 |
|
184 |
void ptytty_delete (PTYTTY ptytty) |
185 |
Destroys the PTYTTY object, freeing the pty/tty pair and cleaning up |
186 |
the utmp/wtmp/lastlog databases, if initialised/used. Same as |
187 |
"delete pty" in C++. |
188 |
|
189 |
int ptytty_get (PTYTTY ptytty) |
190 |
See "pty->get", returns 0 in case of an error, non-zero otherwise. |
191 |
|
192 |
void ptytty_login (PTYTTY ptytty, int cmd_pid, bool login_shell, const |
193 |
char *hostname) |
194 |
See "pty->login". |
195 |
|
196 |
void ptytty_close_tty (PTYTTY ptytty) |
197 |
See "pty->close_tty". |
198 |
|
199 |
int ptytty_make_controlling_tty (PTYTTY ptytty) |
200 |
See "pty->make_controlling_tty". |
201 |
|
202 |
void ptytty_set_utf8_mode (PTYTTY ptytty, int on) |
203 |
See "pty->set_utf8_mode". |
204 |
|
205 |
void ptytty_drop_privileges () |
206 |
See "ptytty::drop_privileges". |
207 |
|
208 |
void ptytty_use_helper () |
209 |
See "ptytty::use_helper". |
210 |
|
211 |
BUGS |
212 |
You kiddin'? |
213 |
|
214 |
AUTHORS |
215 |
Emanuele Giaquinta <e.giaquinta@glauco.it>, Marc Alexander Lehmann |
216 |
<rxvt-unicode@schmorp.de>. |
217 |
|