[LTP] [PATCH v2] Add pty06 test for use-after-free in con_shutdown()

[xiaoshoukui]

adjust coding style and convert comment into assciidoc format.
test on both bug and bug-fix kernels, thanks.

Signed-off-by: xiaoshoukui <xiaoshoukui@ruijie.com.cn>
---
 runtest/pty                     |  1 +
 testcases/kernel/pty/.gitignore |  1 +
 testcases/kernel/pty/Makefile   |  4 +-
 testcases/kernel/pty/pty06.c    | 96 +++++++++++++++++++++++++++++++++
 4 files changed, 100 insertions(+), 2 deletions(-)
 create mode 100644 testcases/kernel/pty/pty06.c

diff --git a/runtest/pty b/runtest/pty
index a43b18f2d..9e5754fab 100644
--- a/runtest/pty
+++ b/runtest/pty
@@ -4,6 +4,7 @@ pty02 pty02
 pty03 pty03
 pty04 pty04
 pty05 pty05
+pty06 pty06
 ptem01 ptem01
 hangup01 hangup01
 
diff --git a/testcases/kernel/pty/.gitignore b/testcases/kernel/pty/.gitignore
index 7f1048483..9b6058cf9 100644
--- a/testcases/kernel/pty/.gitignore
+++ b/testcases/kernel/pty/.gitignore
@@ -5,3 +5,4 @@
 /pty03
 /pty04
 /pty05
+/pty06
diff --git a/testcases/kernel/pty/Makefile b/testcases/kernel/pty/Makefile
index d4c6c87f0..51b7356c2 100644
--- a/testcases/kernel/pty/Makefile
+++ b/testcases/kernel/pty/Makefile
@@ -6,7 +6,7 @@ top_srcdir		?= ../../..
 
 include $(top_srcdir)/include/mk/testcases.mk
 
-pty03 pty05: CFLAGS += -pthread
-pty03 pty05: LDLIBS += -lrt
+pty03 pty05 pty06: CFLAGS += -pthread
+pty03 pty05 pty06: LDLIBS += -lrt
 
 include $(top_srcdir)/include/mk/generic_leaf_target.mk
diff --git a/testcases/kernel/pty/pty06.c b/testcases/kernel/pty/pty06.c
new file mode 100644
index 000000000..bc7aabd70
--- /dev/null
+++ b/testcases/kernel/pty/pty06.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2022 xiaoshoukui <xiaoshoukui@ruijie.com.cn>
+ */
+
+/*\
+ * [Description]
+ *
+ * Test based on Syzkaller reproducer:
+ * https://syzkaller.appspot.com/bug?extid=522643ab5729b0421998
+ *
+ * The VT_DISALLOCATE ioctl can free a virtual console while tty_release()
+ * is still running, causing a use-after-free in con_shutdown().This occurs
+ * because VT_DISALLOCATE only considers a virtual console to be in-use if
+ * it has a tty_struct with count > 0.But actually when count == 0, the tty
+ * is still in the process of being closed.
+ *
+ * Fixed by commit ca4463bf8438:
+ * "vt: vt_ioctl: fix VT_DISALLOCATE freeing in-use virtual console"
+ */
+
+#define _GNU_SOURCE
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <termios.h>
+#include <linux/vt.h>
+#include "lapi/ioctl.h"
+
+#include "tst_test.h"
+#include "tst_safe_stdio.h"
+#include "tst_fuzzy_sync.h"
+
+#define BUF_SIZE 256
+static char tty_path_a[BUF_SIZE];
+static char tty_path_b[BUF_SIZE];
+static int test_tty_port = 8;
+static struct tst_fzsync_pair fzp;
+
+static void *open_close(void *unused)
+{
+	sprintf(tty_path_b, "/dev/tty%d", test_tty_port);
+
+	while (tst_fzsync_run_b(&fzp)) {
+		tst_fzsync_start_race_b(&fzp);
+		int fd = SAFE_OPEN(tty_path_b, O_RDWR);
+
+		SAFE_CLOSE(fd);
+		tst_fzsync_end_race_b(&fzp);
+	}
+
+	return unused;
+}
+
+static void do_test(void)
+{
+	sprintf(tty_path_a, "/dev/tty%d", test_tty_port + 1);
+	int fd = SAFE_OPEN(tty_path_a, O_RDWR);
+
+	tst_fzsync_pair_reset(&fzp, open_close);
+
+	while (tst_fzsync_run_a(&fzp)) {
+		tst_fzsync_start_race_a(&fzp);
+		ioctl(fd, VT_DISALLOCATE, test_tty_port);
+		tst_fzsync_end_race_a(&fzp);
+		if (tst_taint_check()) {
+			tst_res(TFAIL, "Kernel is vulnerable");
+			return;
+		}
+	}
+	SAFE_CLOSE(fd);
+	tst_res(TPASS, "Did not crash with VT_DISALLOCATE");
+}
+
+static void setup(void)
+{
+	tst_fzsync_pair_init(&fzp);
+}
+
+static void cleanup(void)
+{
+	tst_fzsync_pair_cleanup(&fzp);
+}
+
+static struct tst_test test = {
+	.test_all = do_test,
+	.setup = setup,
+	.cleanup = cleanup,
+	.needs_root = 1,
+	.taint_check = TST_TAINT_W | TST_TAINT_D,
+	.tags = (const struct tst_tag[]) {
+	    { "linux-git", "ca4463bf8438"},
+	    {}
+	}
+};
-- 
2.20.1