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Joachim Wiberg
61b0e0f3e6
Apply a PAM session to run/task/sysv/services Finit starts, pam_limits
above all, so a service running as a given user picks up that user's
limits the way a login does.
Add a new `pam` setting for the new block format (only), like the
per-service directories, naming a file in /etc/pam.d:
service weston {
user = "weston"
pam = "weston-autologin"
command = "/usr/bin/weston --continue-without-input"
}
pam_close_session() has to be called by a process still holding the
handle, and the handle does not survive exec(). Hence the keeper: it
holds the handle, drops to the service's credentials, and waits for a
parent-death signal before closing the session. Same shape as
systemd's (sd-pam), for the same reason, and one per fork, so the
script hooks open and close their own.
The keeper closes the descriptors it inherited from Finit and only
those. Closing everything would also take out what pam_open_session()
opened for itself, a keyring fd or a lock file, and leave the modules
to close a session with those pulled out from under them. Closing
nothing, as (sd-pam) does, would leave it holding the write end of the
notify pipe for the service's whole lifetime and starve notify = "s6"
services of their ready signal. So the fds open before pam_start()
are snapshotted and exactly those are closed, while the ones PAM opens
after are marked close-on-exec so the daemon does not inherit them
either.
A refused value, a denied account stack, an uninstalled pam.d file,
and a build without PAM support all keep the service from starting
rather than running it with the stacks skipped: one that quietly loses
pam_limits and its private /tmp, with nothing said. Capabilities a
module like pam_cap.so granted are merged into the IAB Finit applies
instead of being replaced by it, which only helps a service that also
sets capabilities, the other arm being a plain setuid() with nothing
left to restore once permitted is empty.
The test sysroot gains pam_permit.so, pam_deny.so and pam_limits.so,
which ldd cannot see, libpam dlopen()s them, and the test skips when
the host has none to stage. The negative cases pin the exit status
rather than only asserting crashed, which serv reports for any early
exit, so a bad command or an unwritable pidfile cannot pass for a
rejected session.
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
61 lines
2.2 KiB
C
61 lines
2.2 KiB
C
/* Finit PAM session support
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*
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* Copyright (c) 2026 Joachim Wiberg <troglobit@gmail.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#ifndef FINIT_PAM_H_
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#define FINIT_PAM_H_
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#include <string.h> /* strchr(), strlen(), strstr() */
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#include <sys/types.h>
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#include "svc.h"
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/*
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* A pam value names a file in /etc/pam.d, it is not a path, and conf.c
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* stores an over-long value truncated, so a value filling the buffer
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* must not be passed on as some other, shorter name that happens to
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* exist. Both users share this one definition: service_start(), which
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* refuses the service outright, log line and a visible state, and
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* pamsess_open(), which every fork funnels through, including the pre:,
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* post:, ready:, cleanup:, stop and reload scripts that run before
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* service_start() ever does.
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*
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* Returns why the value cannot be used, or NULL when it can.
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*/
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static inline const char *pam_invalid(const char *pam)
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{
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if (!pam[0])
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return NULL;
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if (strlen(pam) >= MAX_ARG_LEN - 1)
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return "is too long";
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if (strchr(pam, '/') || strstr(pam, ".."))
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return "names a file in /etc/pam.d, not a path";
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return NULL;
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}
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int pamsess_open(svc_t *svc, uid_t uid, gid_t gid, char ***envp);
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#endif /* FINIT_PAM_H_ */
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