- Since strncpy(3) is not designed to write strings, but rather
(null-padded) character sequences (a.k.a. unterminated strings), we
had to manually append a '\0'. strlcpy(3) creates strings, so they
are always terminated. This removes dependencies between lines, and
also removes chances of accidents.
- Repurposing strncpy(3) to create strings requires calculating the
location of the terminating null byte, which involves a '-1'
calculation. This is a source of off-by-one bugs. The new code has
no '-1' calculations, so there's almost-zero chance of these bugs.
- strlcpy(3) doesn't padd with null bytes. Padding is relevant when
writing fixed-width buffers to binary files, when interfacing certain
APIs (I believe utmpx requires null padding at lease in some
systems), or when sending them to other processes or through the
network. This is not the case, so padding is effectively ignored.
- strlcpy(3) requires that the input string is really a string;
otherwise it crashes (SIGSEGV). Let's check if the input strings are
really strings:
- lib/fields.c:
- 'cp' was assigned from 'newft', and 'newft' comes from fgets(3).
- lib/gshadow.c:
- strlen(string) is calculated a few lines above.
- libmisc/console.c:
- 'cons' comes from getdef_str, which is a bit cryptic, but seems
to generate strings, I guess.1
- libmisc/date_to_str.c:
- It receives a string literal. :)
- libmisc/utmp.c:
- 'tname' comes from ttyname(3), which returns a string.
- src/su.c:
- 'tmp_name' has been passed to strcmp(3) a few lines above.
Signed-off-by: Alejandro Colomar <alx@kernel.org>
C89 and POSIX.1-2001 define signal(2) as returning a pointer to a
function returning 'void'. K&R C signal(2) signature is obsolete.
Use 'void' directly.
Also, instead of writing the function pointer type explicitly, use
POSIX's 'sighandler_t'.
Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
The SIGCHLD handler could have been ignored by parent process.
Make sure that we have default handling activated.
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
This conforms to PAM documentation and it is needed to support
ambient capabilities with PAM + libcap-2.58+.
Signed-off-by: Björn Fischer <bf@CeBiTec.Uni-Bielefeld.DE>
The buggy code was introduced nearly 5 years ago at the
commit 08fd4b69e8. The
desired behavior is that SIGKILL will be sent to the
child if it does not exit within 2 seconds after it
receives SIGTERM. However, SIGALRM is masked while
waiting for the child so it cannot wake the program
up after 2 seconds to send SIGKILL.
An example shows the buggy behavior, which exists in
Ubuntu 18.04 LTS (with login 1:4.5-1ubuntu2).
```bash
user1@localhost:~$ su user2 -c '
_term() {
echo SIGTERM received
}
trap _term TERM
while true; do
sleep 1
echo still alive
done'
Password:
still alive
Session terminated, terminating shell...Terminated
SIGTERM received
still alive
still alive
still alive
still alive
```
(SIGTERM is sent in another user1's terminal by
executing `killall su`.)
Here is the desired behavior, which shows what the
commit fixes.
```bash
user1@localhost:~$ su user2 -c '
_term() {
echo SIGTERM received
}
trap _term TERM
while true; do
sleep 1
echo still alive
done'
Password:
still alive
Session terminated, terminating shell...Terminated
SIGTERM received
still alive
still alive
...killed.
user1@localhost:~$ echo $?
255
```
Closes#325
Add a new subid_init() function which can be used to specify the
stream on which error messages should be printed. (If you want to
get fancy you can redirect that to memory :) If subid_init() is
not called, use stderr. If NULL is passed, then /dev/null will
be used.
This patch also fixes up the 'Prog', which previously had to be
defined by any program linking against libsubid. Now, by default
in libsubid it will show (subid). Once subid_init() is called,
it will use the first variable passed to subid_init().
Signed-off-by: Serge Hallyn <serge@hallyn.com>
* login & su: Treat an empty passwd field as invalid
Otherwise it's treated like the “require no password” clause while it probably
should be treated like a normal su that can't validate anyway.
A similar change should be done for USE_PAM.
* su & login: Introduce PREVENT_NO_AUTH
It's now possible to run commands as other users without shell
interpolation by using "--exec":
Read /etc/shadow as root without specifying user:
```
su --exec /bin/cat -- /etc/shadow
```
Or specify user:
```
su --exec /bin/cat root -- /etc/shadow
```
Mechanical rename distinguishing this variable from intended changes
supporting executing commands without using an interpretive shell
(i.e. no '/bin/sh -c').
In preparation for supporting --exec I was testing the robustness
of "--" handling and it became apparent that things are currently
a bit broken in `su`.
Since "--" is currently of limited utility, as the subsequent
words are simply passed to the shell after "-c","command_string",
it seems to have gone unnoticed for ages.
However, with --exec, it's expected that "--" would be an almost
required separator with every such usage, considering the
following flags must be passed verbatim to execve() and will
likely begin with hyphens looking indistinguishable from any
other flags in lieu of shell interpolation to worry about.
For some practical context of the existing situation, this
invocation doesn't work today:
```
$ su --command ls -- flags for shell
No passwd entry for user 'flags'
$
```
This should just run ls as root with "flags","for","shell"
forwarded to the shell after "-c","ls".
The "--" should block "flags" from being treated as the user.
That particular issue isn't a getopt one per-se, it's arguably
just a bug in su.c's implementation.
It *seemed* like an easy fix for this would be to add a check if
argv[optind-1] were "--" before treating argv[optind] as USER.
But testing that fix revealed getopt was rearranging things when
encountering "--", the "--" would always separate the handled
opts from the unhandled ones. USER would become shifted to
*after* "--" even when it occurred before it!
If we change the command to specify the user, it works as-is:
```
$ su --command ls root -- flags for shell
Password:
testfile
$
```
But what's rather surprising is how that works; the argv winds up:
"su","--command","ls","--","root","flags","for","shell"
with optind pointing at "root".
That arrangement of argv is indistinguishable from omitting the
user and having "root","flags","for","shell" as the stuff after
"--".
This makes it non-trivial to fix the bug of omitting user
treating the first word after "--" as the user, which one could
argue is a potentially serious security bug if you omit the user,
expect the command to run as root, and the first word after "--"
is a valid user, and what follows that something valid and
potentially destructive not only running in unintended form but
as whatever user happened to be the first word after "--".
So, it seems like something important to fix, and getopt seems to
be getting in the way of fixing it properly without being more
trouble than replacing getopt.
In disbelief of what I was seeing getopt doing with argv here, I
took a glance at the getopt source and found the following:
```
/* The special ARGV-element '--' means premature end of options.
Skip it like a null option,
then exchange with previous non-options as if it were an option,
then skip everything else like a non-option. */
if (d->optind != argc && !strcmp (argv[d->optind], "--"))
```
I basically never use getopt personally because ages ago it
annoyed me with its terrible API for what little it brought to
the table, and this brings it to a whole new level of awful.
When "su -l" is used the behaviour is described as similar to
a direct login. However login.c is doing a setup_env(pw) and then a
pam_getenvlist() in this scenario. But su.c is doing it the other
way around. Which means that the value of PATH from /etc/environment
is overriden. I think this is a bug because:
The man-page claims that "-l": "provides an environment similar
to what the user would expect had the user logged in directly."
And login.c is using the PATH from /etc/environment.
This will fix:
https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/984390
Do not reset the pid_child to 0 if the child process is still
running. This else-condition can be reached with pid being -1,
therefore explicitly test this condition.
This is a regression fix for CVE-2017-2616. If su receives a
signal like SIGTERM, it is not propagated to the child.
Reported-by: Radu Duta <raduduta@gmail.com>
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
If su is compiled with PAM support, it is possible for any local user
to send SIGKILL to other processes with root privileges. There are
only two conditions. First, the user must be able to perform su with
a successful login. This does NOT have to be the root user, even using
su with the same id is enough, e.g. "su $(whoami)". Second, SIGKILL
can only be sent to processes which were executed after the su process.
It is not possible to send SIGKILL to processes which were already
running. I consider this as a security vulnerability, because I was
able to write a proof of concept which unlocked a screen saver of
another user this way.
Some of the supplied tools use functions which are not signal-safe.
Most of the times it's exit() vs. _exit().
In other times it's how the standard output or standard error is
handled. FILE-related functions shall be avoided, therefore I replaced
them with write().
Also there is no need to call closelog(). At worst, it allows to
trigger a deadlock by issuing different signal types at bad timings.
But as these fixes are about race conditions, expect bad timings in
general for these bugs to be triggered. :)
* src/su.c: Terminate the child (if needed) before closing the PAM
session. This is probably more correct, and avoid reporting
termination from signals possibly sent by PAM modules (e.g. former
versions of pam_systemd). Debian#670132
* src/su.c: When a SIGTSTP is caught, reset caught to 0. There is
no need to kill the child in such case after su is resumed. This
remove the "Session terminated, terminating shell...
...terminated." messages in such case.
save_caller_context() is allocated and freed.
* src/su.c: Added missing #endif indication
* src/su.c save_caller_context(): password only needed if
SU_ACCESS and !USE_PAM.
* src/su.c: Added function prototypes.
* src/su.c: Rename shellstr parameter to shellname to avoid
collision with static variable.
* NEWS, src/su.c: Added support for PAM modules which change
PAM_USER.
child and listening for signal in the parent from run_shell().
prepare_pam_close_session() is now executed before the creation of
the pam session and before the UID is changed. This allows to
close the session as root.
