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changing lock mechanism

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Systems can suffer power interruptions whilst .lock files are in /etc,
preventing scripts and other automation tools from updating shadow's
files which persist across boots.

This commit replaces that mechanism with file locking to avoid problems
of power interruption/crashing.

Minor tweak to groupmems man page, requested by 'xx' on IRC.

Signed-off-by: ed neville <ed@s5h.net>
This commit is contained in:
ed neville 2022-12-06 19:21:55 +00:00 committed by Serge Hallyn
parent bc18c184e5
commit 65470e5c7d
3 changed files with 30 additions and 157 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

184
lib/commonio.c
View File

@ -32,8 +32,6 @@
/* local function prototypes */
static int lrename (const char *, const char *);
static int check_link_count (const char *file, bool log);
static int do_lock_file (const char *file, const char *lock, bool log);
static /*@null@*/ /*@dependent@*/FILE *fopen_set_perms (
const char *name,
const char *mode,
@ -91,150 +89,6 @@ int lrename (const char *old, const char *new)
return res;
}
static int check_link_count (const char *file, bool log)
{
struct stat sb;
if (stat (file, &sb) != 0) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: %s file stat error: %s\n",
shadow_progname, file, strerror (errno));
}
return 0;
}
if (sb.st_nlink != 2) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: %s: lock file already used (nlink: %u)\n",
shadow_progname, file, sb.st_nlink);
}
return 0;
}
return 1;
}
static int do_lock_file (const char *file, const char *lock, bool log)
{
int fd;
pid_t pid;
ssize_t len;
int retval;
char buf[32];
fd = open (file, O_CREAT | O_TRUNC | O_WRONLY, 0600);
if (-1 == fd) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: %s: %s\n",
shadow_progname, file, strerror (errno));
}
return 0;
}
pid = getpid ();
snprintf (buf, sizeof buf, "%lu", (unsigned long) pid);
len = (ssize_t) strlen (buf) + 1;
if (write (fd, buf, (size_t) len) != len) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: %s file write error: %s\n",
shadow_progname, file, strerror (errno));
}
(void) close (fd);
unlink (file);
return 0;
}
if (fdatasync (fd) == -1) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: %s file sync error: %s\n",
shadow_progname, file, strerror (errno));
}
(void) close (fd);
unlink (file);
return 0;
}
close (fd);
if (link (file, lock) == 0) {
retval = check_link_count (file, log);
unlink (file);
return retval;
}
fd = open (lock, O_RDWR);
if (-1 == fd) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: %s: %s\n",
shadow_progname, lock, strerror (errno));
}
unlink (file);
errno = EINVAL;
return 0;
}
len = read (fd, buf, sizeof (buf) - 1);
close (fd);
if (len <= 0) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: existing lock file %s without a PID\n",
shadow_progname, lock);
}
unlink (file);
errno = EINVAL;
return 0;
}
buf[len] = '\0';
if (get_pid (buf, &pid) == 0) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: existing lock file %s with an invalid PID '%s'\n",
shadow_progname, lock, buf);
}
unlink (file);
errno = EINVAL;
return 0;
}
if (kill (pid, 0) == 0) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: lock %s already used by PID %lu\n",
shadow_progname, lock, (unsigned long) pid);
}
unlink (file);
errno = EEXIST;
return 0;
}
if (unlink (lock) != 0) {
if (log) {
(void) fprintf (shadow_logfd,
"%s: cannot get lock %s: %s\n",
shadow_progname, lock, strerror (errno));
}
unlink (file);
return 0;
}
retval = 0;
if (link (file, lock) == 0) {
retval = check_link_count (file, log);
} else {
if (log) {
(void) fprintf (shadow_logfd,
"%s: cannot get lock %s: %s\n",
shadow_progname, lock, strerror (errno));
}
}
unlink (file);
return retval;
}
static /*@null@*/ /*@dependent@*/FILE *fopen_set_perms (
const char *name,
@ -349,6 +203,30 @@ bool commonio_present (const struct commonio_db *db)
}
int do_fcntl_lock (const char *file, bool log, short type)
{
int fd;
struct flock lck = {
.l_type = type,
.l_whence = SEEK_SET,
.l_start = 0,
.l_len = 0,
};
fd = open (file, O_WRONLY, 0600);
if (-1 == fd) {
if (log) {
(void) fprintf (shadow_logfd, "%s: %s: %s\n",
shadow_progname, file, strerror (errno));
}
return 0;
}
fcntl (fd, F_OFD_SETLKW, &lck);
close(fd);
return(1);
}
int commonio_lock_nowait (struct commonio_db *db, bool log)
{
char* file = NULL;
@ -372,8 +250,8 @@ int commonio_lock_nowait (struct commonio_db *db, bool log)
}
snprintf (file, file_len, "%s.%lu",
db->filename, (unsigned long) getpid ());
snprintf (lock, lock_file_len, "%s.lock", db->filename);
if (do_lock_file (file, lock, log) != 0) {
if (do_fcntl_lock (db->filename, log, F_WRLCK | F_RDLCK) != 0) {
db->locked = true;
lock_count++;
err = 1;
@ -471,8 +349,6 @@ static void dec_lock_count (void)
int commonio_unlock (struct commonio_db *db)
{
char lock[1024];
if (db->isopen) {
db->readonly = true;
if (commonio_close (db) == 0) {
@ -483,13 +359,9 @@ int commonio_unlock (struct commonio_db *db)
}
}
if (db->locked) {
/*
* Unlock in reverse order: remove the lock file,
* then call ulckpwdf() (if used) on last unlock.
*/
db->locked = false;
snprintf (lock, sizeof lock, "%s.lock", db->filename);
unlink (lock);
do_fcntl_lock (db->filename, false, F_UNLCK);
dec_lock_count ();
return 1;
}

1
lib/commonio.h
View File

@ -123,6 +123,7 @@ extern int commonio_setname (struct commonio_db *, const char *);
extern bool commonio_present (const struct commonio_db *db);
extern int commonio_lock (struct commonio_db *);
extern int commonio_lock_nowait (struct commonio_db *, bool log);
extern int do_fcntl_lock (const char *file, bool log, short type);
extern int commonio_open (struct commonio_db *, int);
extern /*@observer@*/ /*@null@*/const void *commonio_locate (struct commonio_db *, const char *);
extern int commonio_update (struct commonio_db *, const void *);

2
man/groupmems.8.xml
View File

@ -167,7 +167,7 @@
<programlisting>
$ groupadd -r groups
$ chmod 2710 groupmems
$ chown root.groups groupmems
$ chown root:groups groupmems
$ groupmems -g groups -a gk4
</programlisting>
</refsect1>