1 files changed, 153 insertions, 0 deletions
diff --git a/libbb/update_passwd.c b/libbb/update_passwd.c
new file mode 100644
index 0000000..88bc28c
--- /dev/null
+++ b/libbb/update_passwd.c
@@ -0,0 +1,153 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * update_passwd
+ *
+ * update_passwd is a common function for passwd and chpasswd applets;
+ * it is responsible for updating password file (i.e. /etc/passwd or
+ * /etc/shadow) for a given user and password.
+ *
+ * Moved from loginutils/passwd.c by Alexander Shishkin <virtuoso@slind.org>
+ */
+
+#include "libbb.h"
+
+#if ENABLE_SELINUX
+static void check_selinux_update_passwd(const char *username)
+{
+	security_context_t context;
+	char *seuser;
+
+	if (getuid() != (uid_t)0 || is_selinux_enabled() == 0)
+		return;		/* No need to check */
+
+	if (getprevcon_raw(&context) < 0)
+		bb_perror_msg_and_die("getprevcon failed");
+	seuser = strtok(context, ":");
+	if (!seuser)
+		bb_error_msg_and_die("invalid context '%s'", context);
+	if (strcmp(seuser, username) != 0) {
+		if (checkPasswdAccess(PASSWD__PASSWD) != 0)
+			bb_error_msg_and_die("SELinux: access denied");
+	}
+	if (ENABLE_FEATURE_CLEAN_UP)
+		freecon(context);
+}
+#else
+#define check_selinux_update_passwd(username) ((void)0)
+#endif
+
+int FAST_FUNC update_passwd(const char *filename, const char *username,
+			const char *new_pw)
+{
+	struct stat sb;
+	struct flock lock;
+	FILE *old_fp;
+	FILE *new_fp;
+	char *fnamesfx;
+	char *sfx_char;
+	unsigned user_len;
+	int old_fd;
+	int new_fd;
+	int i;
+	int cnt = 0;
+	int ret = -1; /* failure */
+
+	filename = xmalloc_follow_symlinks(filename);
+	if (filename == NULL)
+		return -1;
+
+	check_selinux_update_passwd(username);
+
+	/* New passwd file, "/etc/passwd+" for now */
+	fnamesfx = xasprintf("%s+", filename);
+	sfx_char = &fnamesfx[strlen(fnamesfx)-1];
+	username = xasprintf("%s:", username);
+	user_len = strlen(username);
+
+	old_fp = fopen(filename, "r+");
+	if (!old_fp)
+		goto free_mem;
+	old_fd = fileno(old_fp);
+
+	selinux_preserve_fcontext(old_fd);
+
+	/* Try to create "/etc/passwd+". Wait if it exists. */
+	i = 30;
+	do {
+		// FIXME: on last iteration try w/o O_EXCL but with O_TRUNC?
+		new_fd = open(fnamesfx, O_WRONLY|O_CREAT|O_EXCL, 0600);
+		if (new_fd >= 0) goto created;
+		if (errno != EEXIST) break;
+		usleep(100000); /* 0.1 sec */
+	} while (--i);
+	bb_perror_msg("cannot create '%s'", fnamesfx);
+	goto close_old_fp;
+
+ created:
+	if (!fstat(old_fd, &sb)) {
+		fchmod(new_fd, sb.st_mode & 0777); /* ignore errors */
+		fchown(new_fd, sb.st_uid, sb.st_gid);
+	}
+	new_fp = fdopen(new_fd, "w");
+	if (!new_fp) {
+		close(new_fd);
+		goto unlink_new;
+	}
+
+	/* Backup file is "/etc/passwd-" */
+	*sfx_char = '-';
+	/* Delete old backup */
+	i = (unlink(fnamesfx) && errno != ENOENT);
+	/* Create backup as a hardlink to current */
+	if (i || link(filename, fnamesfx))
+		bb_perror_msg("warning: cannot create backup copy '%s'", fnamesfx);
+	*sfx_char = '+';
+
+	/* Lock the password file before updating */
+	lock.l_type = F_WRLCK;
+	lock.l_whence = SEEK_SET;
+	lock.l_start = 0;
+	lock.l_len = 0;
+	if (fcntl(old_fd, F_SETLK, &lock) < 0)
+		bb_perror_msg("warning: cannot lock '%s'", filename);
+	lock.l_type = F_UNLCK;
+
+	/* Read current password file, write updated /etc/passwd+ */
+	while (1) {
+		char *line = xmalloc_fgets(old_fp);
+		if (!line) break; /* EOF/error */
+		if (strncmp(username, line, user_len) == 0) {
+			/* we have a match with "username:"... */
+			const char *cp = line + user_len;
+			/* now cp -> old passwd, skip it: */
+			cp = strchrnul(cp, ':');
+			/* now cp -> ':' after old passwd or -> "" */
+			fprintf(new_fp, "%s%s%s", username, new_pw, cp);
+			cnt++;
+		} else
+			fputs(line, new_fp);
+		free(line);
+	}
+	fcntl(old_fd, F_SETLK, &lock);
+
+	/* We do want all of them to execute, thus | instead of || */
+	if ((ferror(old_fp) | fflush(new_fp) | fsync(new_fd) | fclose(new_fp))
+	 || rename(fnamesfx, filename)
+	) {
+		/* At least one of those failed */
+		goto unlink_new;
+	}
+	ret = cnt; /* whee, success! */
+
+ unlink_new:
+	if (ret < 0) unlink(fnamesfx);
+
+ close_old_fp:
+	fclose(old_fp);
+
+ free_mem:
+	free(fnamesfx);
+	free((char *)filename);
+	free((char *)username);
+	return ret;
+}