Fix openvt -u process matching to be more conservative (CVE-2026-72693)

2026-08-27 10:17:31 +02:00
2 changed files with 137 additions and 1 deletions
--- a/kbd-2.9.0-CVE-2026-72693.patch
+++ b/kbd-2.9.0-CVE-2026-72693.patch
@ -0,0 +1,129 @@
+diff --git a/docs/man/man1/openvt.1 b/docs/man/man1/openvt.1
+index 8f1244f1..404e4a06 100644
+--- a/docs/man/man1/openvt.1
+++ b/docs/man/man1/openvt.1
+@@ -36,6 +36,8 @@ will be made the new current VT.
+ \fB\-u\fR, \fB\-\-user\fR
+ Figure out the owner of the current VT, and run login as that user.
+ Suitable to be called by init. Shouldn't be used with \fI\-c\fR or \fI\-l\fR.
+This option refuses to pre-authenticate root and requires a process owned by
+the VT owner whose controlling terminal is the current VT.
+ .TP
+ \fB\-l\fR, \fB\-\-login\fR
+ Make the command a login shell. A \- is prepended to the name of the command
+@@ -64,6 +66,14 @@ If
+ is compiled with a getopt_long() and you wish to set
+ options to the command to be run, then you must supply
+ the end of options \-\- flag before the command.
+.PP
+The
+.B \-u
+option uses
+.BR "login -f"
+and therefore bypasses normal password authentication for the detected user.
+It is intended only for controlled init or keyboard-request configurations.
+Use a normal authenticated login command when authentication is required.
+ .SH EXAMPLES
+ .B openvt
+ can be used to start a shell on the next free VT, by using the command:
+diff --git a/src/openvt.c b/src/openvt.c
+index ed3ed18e..dab3dad8 100644
+--- a/src/openvt.c
+++ b/src/openvt.c
+@@ -57,6 +57,51 @@ usage(int rc, const struct kbd_help *options)
+ 	exit(rc);
+ }
+
+static int
+proc_pid_stat(const char *pid, uid_t *uid, dev_t *tty)
+{
+	char filename[NAME_MAX + 12];
+	char line[BUFSIZ];
+	char *lp, *rp;
+	FILE *fp;
+	struct stat st;
+	long tty_nr;
+
+	snprintf(filename, sizeof(filename), "/proc/%s/stat", pid);
+	fp = fopen(filename, "r");
+	if (!fp)
+		return -1;
+
+	if (fstat(fileno(fp), &st)) {
+		fclose(fp);
+		return -1;
+	}
+
+	if (!fgets(line, sizeof(line), fp)) {
+		fclose(fp);
+		return -1;
+	}
+	fclose(fp);
+
+	rp = strrchr(line, ')');
+	if (!rp)
+		return -1;
+
+	/*
+	 * /proc/<pid>/stat fields after comm are:
+	 * state ppid pgrp session tty_nr ...
+	 */
+	if (!rp || sscanf(rp + 1, " %*c %*d %*d %*d %ld", &tty_nr) != 1)
+		return -1;
+
+	if (tty_nr <= 0)
+		return -1;
+
+	*uid = st.st_uid;
+	*tty = (dev_t) tty_nr;
+	return 0;
+}
+
+ /*
+  * Support for Spawn_Console: openvt running from init
+  * added by Joshua Spoerri, Thu Jul 18 21:13:16 EDT 1996
+@@ -88,8 +133,7 @@ authenticate_user(int curvt)
+ 	DIR *dp;
+ 	struct dirent *dentp;
+ 	struct stat buf;
+-	dev_t console_dev;
+-	ino_t console_ino;
+	dev_t console_rdev;
+ 	uid_t console_uid;
+ 	char filename[NAME_MAX + 12];
+ 	struct passwd *pwnam;
+@@ -109,10 +153,12 @@ authenticate_user(int curvt)
+ 			kbd_error(EXIT_FAILURE, errsv, "%s", filename);
+ 		}
+ 	}
+-	console_dev = buf.st_dev;
+-	console_ino = buf.st_ino;
+	console_rdev = buf.st_rdev;
+ 	console_uid = buf.st_uid;
+
+	if (console_uid == 0)
+		kbd_error(EXIT_FAILURE, 0, _("Refusing to pre-authenticate root on current tty."));
+
+ 	/* get the owner of current tty */
+ 	if (!(pwnam = getpwuid(console_uid)))
+ 		kbd_error(EXIT_FAILURE, errno, "getpwuid");
+@@ -120,12 +166,16 @@ authenticate_user(int curvt)
+ 	/* check to make sure that user has a process on that tty */
+ 	/* this will fail for example when X is running on the tty */
+ 	while ((dentp = readdir(dp))) {
+-		sprintf(filename, "/proc/%s/fd/0", dentp->d_name);
+		uid_t proc_uid;
+		dev_t proc_tty;
+
+		if (dentp->d_name[0] < '0' || dentp->d_name[0] > '9')
+			continue;
+
+-		if (stat(filename, &buf))
+		if (proc_pid_stat(dentp->d_name, &proc_uid, &proc_tty) < 0)
+ 			continue;
+
+-		if (buf.st_dev == console_dev && buf.st_ino == console_ino && buf.st_uid == console_uid)
+		if (proc_uid == console_uid && proc_tty == console_rdev)
+ 			goto got_a_process;
+ 	}
+
--- a/kbd.spec
+++ b/kbd.spec
@ -5,7 +5,7 @@

 Name:           kbd
 Version:        2.8.0
-Release:        3%{?dist}
+Release:        4%{?dist}
 Summary:        Tools for configuring the console (keyboard, virtual terminals, etc.)
 License:        GPL-2.0-or-later
 URL:            http://www.kbd-project.org/
@ -34,6 +34,9 @@ Patch5:         kbd-2.0.2-unicode-start-font.patch
 Patch6:         kbd-2.4.0-covscan-fixes.patch
 # Patch7: adds vlock option to issue prompt before invokation of pam stack
 Patch7:         kbd-2.0.4-vlock-add-prompt-option.patch
+# Patch8: fixes CVE-2026-72693, backported from upstream
+# https://github.com/legionus/kbd/commit/78d5ae119742e87baa7dbe0f5c4107e7533fd698
+Patch8:         kbd-2.9.0-CVE-2026-72693.patch

 BuildRequires:  gcc, bison, flex, gettext, pam-devel, check-devel, automake
 BuildRequires:  console-setup, xkeyboard-config
@ -184,6 +187,10 @@ fi
 %{kbd_datadir}/keymaps/legacy

 %changelog
+* Thu Aug 27 2026 Vitezslav Crhonek <vcrhonek@redhat.com> - 2.8.0-4
+- Fix openvt -u process matching to be more conservative (CVE-2026-72693)
+  Resolves: #2513795
+
 * Thu Jul 24 2025 Fedora Release Engineering <releng@fedoraproject.org> - 2.8.0-3
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_43_Mass_Rebuild