Add wrapper for write(2)

write(2) may not write the complete given buffer.  Add a wrapper to
avoid short writes.

lib/Makefile.am

@@ -66,7 +66,8 @@ libshadow_la_SOURCES = \
 	shadowio.c \
 	shadowio.h \
 	shadowmem.c \
-	spawn.c
+	spawn.c \
+	write_full.c
 
 if WITH_TCB
 libshadow_la_SOURCES += tcbfuncs.c tcbfuncs.h

lib/commonio.c

@@ -140,7 +140,7 @@ static int do_lock_file (const char *file, const char *lock, bool log)
 	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 (write_full (fd, buf, (size_t) len) != len) {
 		if (log) {
 			(void) fprintf (shadow_logfd,
 			                "%s: %s file write error: %s\n",

lib/prototypes.h

@@ -526,6 +526,9 @@ extern unsigned long active_sessions_count(const char *name,
 /* valid.c */
 extern bool valid (const char *, const struct passwd *);
 
+/* write_full.c */
+extern ssize_t write_full(int fd, const void *buf, size_t count);
+
 /* xgetpwnam.c */
 extern /*@null@*/ /*@only@*/struct passwd *xgetpwnam (const char *);
 /* xprefix_getpwnam.c */

lib/write_full.c

@@ -0,0 +1,52 @@
+/*
+ * SPDX-FileCopyrightText:  2023, Christian Göttsche <cgzones@googlemail.com>
+ *
+ * SPDX-License-Identifier:  BSD-3-Clause
+ */
+
+
+#include <config.h>
+
+#ident "$Id$"
+
+#include "prototypes.h"
+
+#include <errno.h>
+#include <unistd.h>
+
+
+/*
+ * write_full - write entire buffer
+ *
+ * Write up to count bytes from the buffer starting at buf to the
+ * file referred to by the file descriptor fd.
+ * Retry in case of a short write.
+ *
+ * Returns the number of bytes written on success, -1 on error.
+ */
+ssize_t write_full(int fd, const void *buf, size_t count) {
+	ssize_t written = 0;
+
+	while (count > 0) {
+		ssize_t res;
+
+		res = write(fd, buf, count);
+		if (res < 0) {
+			if (errno == EINTR) {
+				continue;
+			}
+
+			return res;
+		}
+
+		if (res == 0) {
+			break;
+		}
+
+		written += res;
+		buf = (const unsigned char*)buf + res;
+		count -= res;
+	}
+
+	return written;
+}

libmisc/copydir.c

@@ -740,42 +740,6 @@ static int copy_special (const struct path_info *src, const struct path_info *ds
 	return err;
 }
 
-/*
- * full_write - write entire buffer
- *
- * Write up to count bytes from the buffer starting at buf to the
- * file referred to by the file descriptor fd.
- * Retry in case of a short write.
- *
- * Returns the number of bytes written on success, -1 on error.
- */
-static ssize_t full_write(int fd, const void *buf, size_t count) {
-	ssize_t written = 0;
-
-	while (count > 0) {
-		ssize_t res;
-
-		res = write(fd, buf, count);
-		if (res < 0) {
-			if (errno == EINTR) {
-				continue;
-			}
-
-			return res;
-		}
-
-		if (res == 0) {
-			break;
-		}
-
-		written += res;
-		buf = (const unsigned char*)buf + res;
-		count -= res;
-	}
-
-	return written;
-}
-
 /*
  * copy_file - copy a file
  *
@@ -852,7 +816,7 @@ static int copy_file (const struct path_info *src, const struct path_info *dst,
 			break;
 		}
 
-		if (full_write (ofd, buf, cnt) < 0) {
+		if (write_full (ofd, buf, cnt) < 0) {
 			(void) close (ofd);
 			(void) close (ifd);
 			return -1;

libmisc/failure.c

@@ -17,6 +17,7 @@
 #include "defines.h"
 #include "faillog.h"
 #include "failure.h"
+#include "prototypes.h"
 #define	YEAR	(365L*DAY)
 /*
  * failure - make failure entry
@@ -85,7 +86,7 @@ void failure (uid_t uid, const char *tty, struct faillog *fl)
 	 */
 
 	if (   (lseek (fd, offset_uid, SEEK_SET) != offset_uid)
-	    || (write (fd, fl, sizeof *fl) != (ssize_t) sizeof *fl)
+	    || (write_full (fd, fl, sizeof *fl) != (ssize_t) sizeof *fl)
 	    || (close (fd) != 0)) {
 		SYSLOG ((LOG_WARN,
 		         "Can't write faillog entry for UID %lu in %s.",
@@ -184,7 +185,7 @@ int failcheck (uid_t uid, struct faillog *fl, bool failed)
 		fail.fail_cnt = 0;
 
 		if (   (lseek (fd, offset_uid, SEEK_SET) != offset_uid)
-		    || (write (fd, &fail, sizeof fail) != (ssize_t) sizeof fail)
+		    || (write_full (fd, &fail, sizeof fail) != (ssize_t) sizeof fail)
 		    || (close (fd) != 0)) {
 			SYSLOG ((LOG_WARN,
 			         "Can't reset faillog entry for UID %lu in %s.",

libmisc/idmapping.c

@@ -215,7 +215,7 @@ void write_mapping(int proc_dir_fd, int ranges, const struct map_range *mappings
 			log_get_progname(), map_file, strerror(errno));
 		exit(EXIT_FAILURE);
 	}
-	if (write(fd, buf, pos - buf) != (pos - buf)) {
+	if (write_full(fd, buf, pos - buf) != (pos - buf)) {
 		fprintf(log_get_logfd(), _("%s: write to %s failed: %s\n"),
 			log_get_progname(), map_file, strerror(errno));
 		exit(EXIT_FAILURE);

libmisc/log.c

@@ -82,7 +82,7 @@ void dolastlog (
 	strncpy (newlog.ll_host, host, sizeof (newlog.ll_host) - 1);
 #endif
 	if (   (lseek (fd, offset, SEEK_SET) != offset)
-	    || (write (fd, &newlog, sizeof newlog) != (ssize_t) sizeof newlog)
+	    || (write_full (fd, &newlog, sizeof newlog) != (ssize_t) sizeof newlog)
 	    || (close (fd) != 0)) {
 		SYSLOG ((LOG_WARN,
 		         "Can't write lastlog entry for UID %lu in %s.",

libmisc/utmp.c

@@ -97,7 +97,7 @@ static void failtmp (const char *username, const struct utmp *failent)
 	 * Append the new failure record and close the log file.
 	 */
 
-	if (   (write (fd, failent, sizeof *failent) != (ssize_t) sizeof *failent)
+	if (   (write_full (fd, failent, sizeof *failent) != (ssize_t) sizeof *failent)
 	    || (close (fd) != 0)) {
 		SYSLOG ((LOG_WARN,
 		         "Can't append failure of user %s to %s.",
@@ -194,7 +194,7 @@ static void updwtmp (const char *filename, const struct utmp *ut)
 
 	fd = open (filename, O_APPEND | O_WRONLY, 0);
 	if (fd >= 0) {
-		write (fd, ut, sizeof (*ut));
+		write_full (fd, ut, sizeof (*ut));
 		close (fd);
 	}
 }

src/login.c

@@ -400,7 +400,7 @@ static void exit_handler (unused int sig)
 
 static void alarm_handler (unused int sig)
 {
-	write (STDERR_FILENO, tmsg, strlen (tmsg));
+	write_full (STDERR_FILENO, tmsg, strlen (tmsg));
 	signal(SIGALRM, exit_handler);
 	alarm(2);
 }

src/su.c

@@ -164,9 +164,9 @@ static void kill_child (int unused(s))
 {
 	if (0 != pid_child) {
 		(void) kill (-pid_child, SIGKILL);
-		(void) write (STDERR_FILENO, kill_msg, strlen (kill_msg));
+		(void) write_full (STDERR_FILENO, kill_msg, strlen (kill_msg));
 	} else {
-		(void) write (STDERR_FILENO, wait_msg, strlen (wait_msg));
+		(void) write_full (STDERR_FILENO, wait_msg, strlen (wait_msg));
 	}
 	_exit (255);
 }

src/useradd.c

@@ -2067,7 +2067,7 @@ static void faillog_reset (uid_t uid)
 		return;
 	}
 	if (   (lseek (fd, offset_uid, SEEK_SET) != offset_uid)
-	    || (write (fd, &fl, sizeof (fl)) != (ssize_t) sizeof (fl))
+	    || (write_full (fd, &fl, sizeof (fl)) != (ssize_t) sizeof (fl))
 	    || (fsync (fd) != 0)) {
 		fprintf (stderr,
 		         _("%s: failed to reset the faillog entry of UID %lu: %s\n"),
@@ -2112,7 +2112,7 @@ static void lastlog_reset (uid_t uid)
 		return;
 	}
 	if (   (lseek (fd, offset_uid, SEEK_SET) != offset_uid)
-	    || (write (fd, &ll, sizeof (ll)) != (ssize_t) sizeof (ll))
+	    || (write_full (fd, &ll, sizeof (ll)) != (ssize_t) sizeof (ll))
 	    || (fsync (fd) != 0)) {
 		fprintf (stderr,
 		         _("%s: failed to reset the lastlog entry of UID %lu: %s\n"),

src/usermod.c

@@ -1941,7 +1941,7 @@ static void update_lastlog (void)
 	    && (read (fd, &ll, sizeof ll) == (ssize_t) sizeof ll)) {
 		/* Copy the old entry to its new location */
 		if (   (lseek (fd, off_newuid, SEEK_SET) != off_newuid)
-		    || (write (fd, &ll, sizeof ll) != (ssize_t) sizeof ll)
+		    || (write_full (fd, &ll, sizeof ll) != (ssize_t) sizeof ll)
 		    || (fsync (fd) != 0)) {
 			fprintf (stderr,
 			         _("%s: failed to copy the lastlog entry of user %lu to user %lu: %s\n"),
@@ -1957,7 +1957,7 @@ static void update_lastlog (void)
 			/* Reset the new uid's lastlog entry */
 			memzero (&ll, sizeof (ll));
 			if (   (lseek (fd, off_newuid, SEEK_SET) != off_newuid)
-			    || (write (fd, &ll, sizeof ll) != (ssize_t) sizeof ll)
+			    || (write_full (fd, &ll, sizeof ll) != (ssize_t) sizeof ll)
 			    || (fsync (fd) != 0)) {
 				fprintf (stderr,
 				         _("%s: failed to copy the lastlog entry of user %lu to user %lu: %s\n"),
@@ -2001,7 +2001,7 @@ static void update_faillog (void)
 	    && (read (fd, &fl, sizeof fl) == (ssize_t) sizeof fl)) {
 		/* Copy the old entry to its new location */
 		if (   (lseek (fd, off_newuid, SEEK_SET) != off_newuid)
-		    || (write (fd, &fl, sizeof fl) != (ssize_t) sizeof fl)
+		    || (write_full (fd, &fl, sizeof fl) != (ssize_t) sizeof fl)
 		    || (fsync (fd) != 0)) {
 			fprintf (stderr,
 			         _("%s: failed to copy the faillog entry of user %lu to user %lu: %s\n"),
@@ -2017,7 +2017,7 @@ static void update_faillog (void)
 			/* Reset the new uid's faillog entry */
 			memzero (&fl, sizeof (fl));
 			if (   (lseek (fd, off_newuid, SEEK_SET) != off_newuid)
-			    || (write (fd, &fl, sizeof fl) != (ssize_t) sizeof fl)) {
+			    || (write_full (fd, &fl, sizeof fl) != (ssize_t) sizeof fl)) {
 				fprintf (stderr,
 				         _("%s: failed to copy the faillog entry of user %lu to user %lu: %s\n"),
 				         Prog, (unsigned long) user_id, (unsigned long) user_newid, strerror (errno));