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contrib/pam_xdg/pam_xdg.c

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/*@ pam_xdg - manage XDG Base Directories (runtime dir life time, environment).
*@ See pam_xdg.8 for more.
*@ - According to XDG Base Directory Specification, v0.7.
*@ - Supports libpam (Linux) and OpenPAM.
*@ - Requires C preprocessor with __VA_ARGS__ support!
*@ - Uses "rm -rf" to drop per-user directories. XXX Unroll this? nftw?
*
* Copyright (c) 2021 Steffen Nurpmeso <steffen@sdaoden.eu>.
* SPDX-License-Identifier: ISC
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/* For these a leading \1 is replaced with struct passwd::pw_dir.
* Be aware we use a stack buffer for storage */
#define a_XDG_DATA_HOME_DEF "\1/.local/share"
#define a_XDG_CONFIG_HOME_DEF "\1/.config"
#define a_XDG_DATA_DIRS_DEF "/usr/local/share:/usr/share"
#define a_XDG_CONFIG_DIRS_DEF "/etc/xdg/"
#define a_XDG_CACHE_HOME_DEF "\1/.cache"
/* We create the outer directories as necessary (stack buffer storage!) */
#define a_RUNTIME_DIR_OUTER "/run"
#define a_RUNTIME_DIR_OUTER_MODE 0755
#define a_RUNTIME_DIR_BASE "user"
#define a_RUNTIME_DIR_BASE_MODE 0755 /* 0711? */
/* Note: we manage these relative to the per-user directory!
* a_LOCK_FILE is only used without "per_user_lock" */
#define a_LOCK_FILE "../." a_XDG ".lck"
#define a_LOCK_TRIES 10
#define a_DAT_FILE "." a_XDG ".dat"
/* >8 -- 8< */
/*
#define _POSIX_C_SOURCE 200809L
#define _ATFILE_SOURCE
*/
#define _GNU_SOURCE /* Always the same mess */
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <pwd.h>
#include <stdint.h> /* xxx not, actually!?! */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <security/pam_appl.h>
#include <security/pam_modules.h>
#ifdef OPENPAM_VERSION
# include <security/openpam.h>
#else
# include <security/pam_ext.h>
#endif
#ifdef OPENPAM_VERSION
#else
# include <syslog.h>
#endif
/* Who are we? */
#define a_XDG "pam_xdg"
/* _XOPEN_PATH_MAX POSIX 2008/Cor 1-2013 */
#ifndef PATH_MAX
# define PATH_MAX 1024
#endif
/* */
#ifdef O_SEARCH
# define a_O_SEARCH O_SEARCH
#elif defined O_PATH
# define a_O_SEARCH O_PATH
#else
/* Well, hardly, but not in practice so do not #error out */
# define a_O_SEARCH 0
#endif
/* libpam / OpenPAM compat */
#ifdef OPENPAM_VERSION
# define a_LOG(HDL, LVL, ...) ((void)HDL, openpam_log(LVL, __VA_ARGS__))
# define a_LOG_ERR PAM_LOG_ERROR
# define a_LOG_NOTICE PAM_LOG_NOTICE
#else
# define a_LOG(HDL, LVL, ...) pam_syslog(HDL, LVL, __VA_ARGS__)
# define a_LOG_ERR LOG_ERR
# define a_LOG_NOTICE LOG_NOTICE
#endif
/* Just put it all in one big fun, use two exec paths */
static int a_xdg(int isopen, pam_handle_t *pamh, int flags, int argc,
const char **argv);
static int
a_xdg(int isopen, pam_handle_t *pamh, int flags, int argc, const char **argv){
enum a_flags{
a_NONE,
/* Options */
a_RUNTIME = 1u<<0,
a_NOTROOT = 1u<<1,
a_SESSIONS = 1u<<16,
a_USER_LOCK = 1u<<17,
/* Flags */
a_MPV = 1u<<29, /* Multi-Purpose-Vehicle */
a_SKIP_XDG = 1u<<30 /* We shall not act */
};
struct a_dirtree{
char const *name;
int mode;
};
static struct a_dirtree const a_dirtree[] = {
{a_RUNTIME_DIR_OUTER, a_RUNTIME_DIR_OUTER_MODE},
{a_RUNTIME_DIR_BASE, a_RUNTIME_DIR_BASE_MODE},
{NULL, 0} /* XXX -> nelem/item/countof */
};
static int f_saved;
char uidbuf[sizeof "../.18446744073709551615"],
xbuf[((sizeof("XDG_RUNTIME_DIR=") + sizeof(a_RUNTIME_DIR_OUTER) +
sizeof(a_RUNTIME_DIR_BASE) +
sizeof("../.18446744073709551615")) |
(sizeof("XDG_CONFIG_DIRS=") + PATH_MAX)
) +1];
struct a_dirtree dt_user;
struct a_dirtree const *dtp;
struct passwd *pwp;
char const *emsg;
int cwdfd, cntrlfd, datfd, f, res, uidbuflen;
char const *user;
user = "<unset>";
cwdfd = AT_FDCWD;
datfd = cntrlfd = -1;
/* Command line */
if(isopen){
f = a_NONE;
for(; argc > 0; ++argv, --argc){
if(!strcmp(argv[0], "runtime"))
f |= a_RUNTIME;
else if(!strcmp(argv[0], "rundir")){ /* XXX COMPAT */
a_LOG(pamh, a_LOG_NOTICE,
a_XDG ": \"rundir\" was a misdocumentation of \"runtime\", "
"sorry for this");
f |= a_RUNTIME;
}
else if(!strcmp(argv[0], "notroot"))
f |= a_NOTROOT;
else if(!strcmp(argv[0], "track_sessions"))
f |= a_SESSIONS;
else if(!strcmp(argv[0], "per_user_lock"))
f |= a_USER_LOCK;
else if(!(flags & PAM_SILENT)){
emsg = "command line";
errno = EINVAL;
goto jerr;
}
}
if((f & a_USER_LOCK) && !(f & a_SESSIONS))
a_LOG(pamh, a_LOG_NOTICE,
a_XDG ": \"per_user_lock\" requires \"track_sessions\"");
}else{
f = f_saved;
if(f & a_SKIP_XDG)
goto jok;
}
/* We need the user we go for */
if((res = pam_get_item(pamh, PAM_USER, (void const**)&user)
) != PAM_SUCCESS){
user = "<lookup failed>";
emsg = "cannot query PAM_USER name";
goto jepam;
}
/* No PAM failure, no PAM_USER_UNKNOWN here: we are no authentificator! */
if((pwp = getpwnam(user)) == NULL){
emsg = "host does not know about user";
errno = EINVAL;
goto jerr;
}
if((f & a_NOTROOT) && pwp->pw_uid == 0){
f |= a_SKIP_XDG;
goto jok;
}
/* Our lockfile and per-user directory name */
uidbuflen = snprintf(uidbuf, sizeof(uidbuf), "../.%lu", /* xxx error?? */
(unsigned long)pwp->pw_uid) - 3;
dt_user.name = &uidbuf[4];
dt_user.mode = 0700; /* XDG implied */
/* Handle tree, go to user runtime. On *BSD outermost may not exist! */
for(/*f &= ~a_MPV,*/ dtp = a_dirtree;;){
int e;
gid_t oegid;
mode_t oumask;
if((res = openat(cwdfd, dtp->name,
(a_O_SEARCH | O_DIRECTORY | O_NOFOLLOW))) != -1){
if(cwdfd != AT_FDCWD)
close(cwdfd); /* XXX error hdl */
cwdfd = res;
if(dtp == &dt_user)
break;
else if((++dtp)->name == NULL)
dtp = &dt_user;
f &= ~a_MPV;
continue;
}
if(!isopen)
/* XXX Entire directory tree disappeared while sessions were open!
* XXX Silently out!?! */
goto jok;
/* We try creating the directories once as necessary */
if((f & a_MPV) || errno != ENOENT){
emsg = "cannot obtain chdir(2) descriptor (within) tree "
a_RUNTIME_DIR_OUTER "/" a_RUNTIME_DIR_BASE;
goto jerr;
}
f |= a_MPV;
oumask = umask(0000);
oegid = getegid();
setegid(0);
res = mkdirat(cwdfd, dtp->name, dtp->mode);
e = (res == -1) ? errno : 0;
setegid(oegid);
umask(oumask);
if(res == -1){
if(e != EEXIST){
emsg = "cannot create directory (within) tree "
a_RUNTIME_DIR_OUTER "/" a_RUNTIME_DIR_BASE;
goto jerr;
}
}else if(cwdfd == AT_FDCWD)
a_LOG(pamh, a_LOG_NOTICE,
a_XDG ": " a_RUNTIME_DIR_OUTER " did not exist, but should be "
"(a mount point of) volatile storage!");
/* Just chown it! */
else if(dtp == &dt_user &&
fchownat(cwdfd, &uidbuf[4], pwp->pw_uid, pwp->pw_gid,
AT_SYMLINK_NOFOLLOW) == -1){
emsg = "cannot chown(2) per user XDG_RUNTIME_DIR";
goto jerr;
}
}
/* In session mode we have to manage the counter file */
if(f & a_SESSIONS){
unsigned long long int sessions;
/* Landed in the runtime base dir, obtain our lock */
if((cntrlfd = openat(cwdfd,
(f & a_USER_LOCK ? uidbuf : a_LOCK_FILE),
(O_CREAT | O_WRONLY | O_NOFOLLOW | O_NOCTTY),
(S_IRUSR | S_IWUSR))) == -1){
emsg = "cannot open control lock file";
goto jerr;
}
for(res = a_LOCK_TRIES;;){
struct flock flp;
memset(&flp, 0, sizeof flp);
flp.l_type = F_WRLCK;
flp.l_start = 0;
flp.l_whence = SEEK_SET;
flp.l_len = 0;
if(fcntl(cntrlfd, F_SETLKW, &flp) != -1)
break;
/* XXX It may happen we cannot manage the lock and thus not access
* XXX the session counter, ie this session is zombie to us.
* XXX Just like counter below, should globally disable sessions!! */
if(errno != EINTR){
emsg = "unexpected error obtaining lock on lock control file";
goto jerr;
}
if(--res == 0){
emsg = "cannot obtain lock on lock control file";
goto jerr;
}
}
sessions = 0;
if((datfd = openat(cwdfd, a_DAT_FILE, O_RDONLY)) != -1){
char *ep;
ssize_t r;
while((r = read(datfd, xbuf, sizeof(xbuf) -1)) == -1){
if(errno != EINTR)
goto jecnt;
}
close(datfd);
datfd = -1;
xbuf[(size_t)r] = '\0';
sessions = strtoull(xbuf, &ep, 10);
/* Do not log too often for "session counter error"s, as below */
if(ep == xbuf){
res = PAM_SESSION_ERR;
goto jleave;
}else if(sessions == ULLONG_MAX || ep != &xbuf[(size_t)r])
goto jecnt;
}
if(isopen)
++sessions;
else if(sessions > 0)
--sessions;
if(!isopen && sessions == 0){ /* former.. hmmm. */
/* Ridiculously simple, but everything else would be the opposite.
* Ie, E[MN]FILE failures, or whatever else */
char const cmd[] = "rm -rf " a_RUNTIME_DIR_OUTER "/"
a_RUNTIME_DIR_BASE "/";
memcpy(xbuf, cmd, sizeof(cmd) -1);
memcpy(&xbuf[sizeof(cmd) -1], &uidbuf[4], uidbuflen +1);
res = system(xbuf);
if(!WIFEXITED(res) || WEXITSTATUS(res) != 0){
emsg = "unable to rm(1) -rf per user XDG_RUNTIME_DIR";
errno = EINVAL;
goto jerr;
}
/* This is the end .. */
goto jok;
}else{
/* Write out session counter */
res = snprintf(xbuf, sizeof xbuf, "%llu", sessions); /* xxx error? */
if(((datfd = openat(cwdfd, a_DAT_FILE,
(O_CREAT | O_TRUNC | O_WRONLY | O_SYNC | O_NOFOLLOW |
O_NOCTTY),
(S_IRUSR | S_IWUSR))) == -1) ||
write(datfd, xbuf, res) != res){
jecnt:
/* Ensure read above fails, so that henceforth session teardown is
* skipped for this user */
truncate(a_DAT_FILE, 0);
emsg = "counter file error, disabled session tracking for user";
goto jerr;
}
close(datfd);
datfd = -1;
}
}
/* When opening, we want to put environment variables, too */
if(isopen){
char *cp;
/* XDG_RUNTIME_DIR */
cp = xbuf;
memcpy(cp, "XDG_RUNTIME_DIR=", sizeof("XDG_RUNTIME_DIR=") -1);
cp += sizeof("XDG_RUNTIME_DIR=") -1;
memcpy(cp, a_RUNTIME_DIR_OUTER, sizeof(a_RUNTIME_DIR_OUTER) -1);
cp += sizeof(a_RUNTIME_DIR_OUTER) -1;
*cp++ = '/';
memcpy(cp, a_RUNTIME_DIR_BASE, sizeof(a_RUNTIME_DIR_BASE) -1);
cp += sizeof(a_RUNTIME_DIR_BASE) -1;
*cp++ = '/';
memcpy(cp, &uidbuf[4], uidbuflen);
if((res = pam_putenv(pamh, xbuf)) != PAM_SUCCESS)
goto jepam;
/* And the rest unless disallowed */
if(!(f & a_RUNTIME)){
struct a_dir{
char const *name;
size_t len;
char const *defval;
};
static struct a_dir const a_dirs[] = {
{"XDG_DATA_HOME=", sizeof("XDG_DATA_HOME=") -1,
a_XDG_DATA_HOME_DEF},
{"XDG_CONFIG_HOME=", sizeof("XDG_CONFIG_HOME=") -1,
a_XDG_CONFIG_HOME_DEF},
{"XDG_DATA_DIRS=", sizeof("XDG_DATA_DIRS=") -1,
a_XDG_DATA_DIRS_DEF},
{"XDG_CONFIG_DIRS=", sizeof("XDG_CONFIG_DIRS=") -1,
a_XDG_CONFIG_DIRS_DEF},
{"XDG_CACHE_HOME=", sizeof("XDG_CACHE_HOME=") -1,
a_XDG_CACHE_HOME_DEF},
{NULL,0,NULL} /* XXX -> nelem/item/countof */
};
char const *src;
struct a_dir const *adp;
size_t i;
i = strlen(pwp->pw_dir);
for(adp = a_dirs; adp->name != NULL; ++adp){
cp = xbuf;
memcpy(cp, adp->name, adp->len);
cp += adp->len;
if(*(src = adp->defval) == '\1'){
memcpy(cp, pwp->pw_dir, i);
cp += i;
++src;
}
memcpy(cp, src, strlen(src) +1);
if((res = pam_putenv(pamh, xbuf)) != PAM_SUCCESS)
goto jepam;
}
}
}
jok:
res = PAM_SUCCESS;
jleave:
if(datfd != -1)
close(datfd);
if(cntrlfd != -1)
close(cntrlfd);
if(cwdfd != -1 && cwdfd != AT_FDCWD) /* >=0, but AT_FDCWD unspecified */
close(cwdfd);
f_saved = f;
return (res == PAM_SUCCESS) ? PAM_SUCCESS : PAM_SESSION_ERR;
jerr:
a_LOG(pamh, a_LOG_ERR, a_XDG ": user %s: %s: %s\n",
user, emsg, strerror(errno));
f |= a_SKIP_XDG;
res = PAM_SESSION_ERR;
goto jleave;
jepam:
a_LOG(pamh, a_LOG_ERR, a_XDG ": user %s: PAM failure: %s\n",
user, pam_strerror(pamh, res));
f |= a_SKIP_XDG;
goto jleave;
}
int
pam_sm_open_session(pam_handle_t *pamh, int flags,
int argc, const char **argv){
return a_xdg(1, pamh, flags, argc, argv);
}
int
pam_sm_close_session(pam_handle_t *pamh, int flags,
int argc, const char **argv){
return a_xdg(0, pamh, flags, argc, argv);
}
int
pam_sm_acct_mgmt(pam_handle_t *pamh, int flags, int argc, const char **argv){
(void)flags;
(void)argc;
(void)argv;
a_LOG(pamh, a_LOG_NOTICE, a_XDG ": pam_sm_acct_mgmt not used");
return PAM_SERVICE_ERR;
}
int
pam_sm_setcred(pam_handle_t *pamh, int flags, int argc, const char **argv){
(void)flags;
(void)argc;
(void)argv;
a_LOG(pamh, a_LOG_NOTICE, a_XDG ": pam_sm_setcred not used");
return PAM_SERVICE_ERR;
}
int
pam_sm_chauthtok(pam_handle_t *pamh, int flags, int argc, const char **argv){
(void)flags;
(void)argc;
(void)argv;
a_LOG(pamh, a_LOG_NOTICE, a_XDG ": pam_sm_chauthtok not used");
return PAM_SERVICE_ERR;
}
/* s-it-mode */
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