[LTP] [PATCH v16 2/2] open16: allow restricted O_CREAT of FIFOs and regular files

[Wei Gao via ltp <ltp@lists.linux.it>]

Add LTP coverage for kernel commit 30aba6656f61 (Linux 4.19), which
introduced protection against spoofing attacks via O_CREAT of FIFOs
and regular files in world-writable or group-writable sticky
directories.

This commit adds test cases to verify these security restrictions
(values 1 and 2 for protected_fifos and protected_regular) for opening
FIFOs and regular files in world-writable or group-writable sticky
directories when the file is not owned by the opener.

Signed-off-by: Wei Gao <wegao@suse.com>
Reviewed-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
 include/tst_path_defs.h                   |   2 +
 runtest/syscalls                          |   1 +
 testcases/kernel/syscalls/open/.gitignore |   1 +
 testcases/kernel/syscalls/open/open16.c   | 143 ++++++++++++++++++++++
 4 files changed, 147 insertions(+)
 create mode 100644 testcases/kernel/syscalls/open/open16.c

diff --git a/include/tst_path_defs.h b/include/tst_path_defs.h
index 1a60028d3..2995150be 100644
--- a/include/tst_path_defs.h
+++ b/include/tst_path_defs.h
@@ -47,6 +47,8 @@
 #define PATH_FS_PIPE_MAX_PAGES			"/proc/sys/fs/pipe-max-pages"
 #define PATH_FS_MAX_USER_GROUPS			"/proc/sys/fs/fanotify/max_user_groups"
 #define PATH_FS_MAX_USER_MARKS			"/proc/sys/fs/fanotify/max_user_marks"
+#define PATH_FS_PROTECTED_REGULAR		"/proc/sys/fs/protected_regular"
+#define PATH_FS_PROTECTED_FIFOS			"/proc/sys/fs/protected_fifos"
 
 /* VM */
 #define PATH_VM_DROP_CACHES			"/proc/sys/vm/drop_caches"
diff --git a/runtest/syscalls b/runtest/syscalls
index a021c79da..4fd62efa8 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -1008,6 +1008,7 @@ open12 open12
 open13 open13
 open14 open14
 open15 open15
+open16 open16
 
 openat01 openat01
 openat02 openat02
diff --git a/testcases/kernel/syscalls/open/.gitignore b/testcases/kernel/syscalls/open/.gitignore
index af5997572..d2cacc02e 100644
--- a/testcases/kernel/syscalls/open/.gitignore
+++ b/testcases/kernel/syscalls/open/.gitignore
@@ -13,3 +13,4 @@
 /open13
 /open14
 /open15
+/open16
diff --git a/testcases/kernel/syscalls/open/open16.c b/testcases/kernel/syscalls/open/open16.c
new file mode 100644
index 000000000..a8d33870f
--- /dev/null
+++ b/testcases/kernel/syscalls/open/open16.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Wei Gao <wegao@suse.com>
+ */
+
+/*\
+ * Verify restricted opening (:manpage:`open(2)` and :manpage:`openat(2)`) of
+ * FIFOs and regular files in sticky directories. This protection is controlled via
+ * ``/proc/sys/fs/protected_fifos`` and ``/proc/sys/fs/protected_regular`` sysctl values:
+ *
+ * - When set to "0", writing/opening is unrestricted.
+ * - When set to "1", O_CREAT open on FIFOs/regular files we don't own in world-writable
+ *   sticky directories is disallowed, unless they are owned by the owner of the directory.
+ * - When set to "2", the same restriction also applies to group-writable sticky directories.
+ *
+ * This test requires root to modify ``/proc/sys/fs/protected_*`` sysctls and
+ * to manage file ownership and permissions in sticky directories.
+ */
+
+#include <pwd.h>
+#include <stdlib.h>
+#include "tst_test.h"
+#include "tst_safe_file_at.h"
+#include "tst_uid.h"
+
+#define DIR "ltp_tmp_check1"
+#define TEST_FILE "test_file_1"
+#define TEST_FIFO "test_fifo_1"
+#define TEST_FIFO_PATH DIR "/" TEST_FIFO
+
+static int dir_fd = -1;
+static uid_t uid1, uid2;
+static gid_t gid1;
+
+static struct tcase {
+	int exp_errno;
+	uid_t owner_uid;
+	int use_nobody_gid;
+	mode_t dir_mode;
+} tcases[] = {
+	{
+		.dir_mode = 0777 | S_ISVTX,
+	},
+	{
+		.exp_errno = EACCES,
+		.dir_mode = 0777 | S_ISVTX,
+	},
+	{
+		.exp_errno = EACCES,
+		.owner_uid = -1,
+		.use_nobody_gid = 1,
+		.dir_mode = 0030 | S_ISVTX,
+	},
+};
+
+static void verify_open(unsigned int n)
+{
+	struct tcase *tc = &tcases[n];
+
+	SAFE_FILE_PRINTF(PATH_FS_PROTECTED_REGULAR, "%u", n);
+	SAFE_FILE_PRINTF(PATH_FS_PROTECTED_FIFOS, "%u", n);
+
+	if (tc->owner_uid != (uid_t)-1 || tc->use_nobody_gid) {
+		gid_t gid = tc->use_nobody_gid ? gid1 : 0;
+
+		SAFE_CHOWN(DIR, tc->owner_uid, gid);
+	}
+
+	if (tc->dir_mode)
+		SAFE_CHMOD(DIR, tc->dir_mode);
+
+	if (SAFE_FORK())
+		return;
+
+	SAFE_SETGID(gid1);
+	SAFE_SETUID(uid2);
+
+	TST_EXP_FD_OR_FAIL(openat(dir_fd, TEST_FILE, O_RDWR | O_CREAT, 0777),
+			   tc->exp_errno, "openat %s (sysctl_val=%u)", TEST_FILE, n);
+	if (TST_RET != -1)
+		SAFE_CLOSE(TST_RET);
+
+	TST_EXP_FD_OR_FAIL(open(TEST_FIFO_PATH, O_RDWR | O_CREAT, 0777),
+			   tc->exp_errno, "open %s (sysctl_val=%u)", TEST_FIFO, n);
+	if (TST_RET != -1)
+		SAFE_CLOSE(TST_RET);
+
+	exit(0);
+}
+
+static void setup(void)
+{
+	struct passwd *pw;
+
+	pw = SAFE_GETPWNAM("nobody");
+	uid1 = pw->pw_uid;
+	gid1 = pw->pw_gid;
+	uid2 = tst_get_free_uid(uid1);
+
+	umask(0);
+	SAFE_MKDIR(DIR, 0777 | S_ISVTX);
+	dir_fd = SAFE_OPEN(DIR, O_DIRECTORY);
+
+	int fd = SAFE_OPENAT(dir_fd, TEST_FILE, O_CREAT | O_RDWR, 0777);
+
+	SAFE_CLOSE(fd);
+	SAFE_MKFIFO(TEST_FIFO_PATH, 0777);
+	SAFE_CHOWN(TEST_FIFO_PATH, uid1, gid1);
+	SAFE_CHOWN(DIR "/" TEST_FILE, uid1, gid1);
+}
+
+static void cleanup(void)
+{
+	if (dir_fd != -1)
+		SAFE_CLOSE(dir_fd);
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.cleanup = cleanup,
+	.needs_root = 1,
+	.tcnt = ARRAY_SIZE(tcases),
+	.test = verify_open,
+	.needs_tmpdir = 1,
+	.forks_child = 1,
+	.save_restore = (const struct tst_path_val[]) {
+		{PATH_FS_PROTECTED_REGULAR, NULL, TST_SR_TCONF},
+		{PATH_FS_PROTECTED_FIFOS, NULL, TST_SR_TCONF},
+		{}
+	},
+	.tags = (const struct tst_tag[]) {
+		{"linux-git", "30aba6656f61"},
+		{"CVE", "2000-1134"},
+		{"CVE", "2007-3852"},
+		{"CVE", "2008-0525"},
+		{"CVE", "2009-0416"},
+		{"CVE", "2011-4834"},
+		{"CVE", "2015-1838"},
+		{"CVE", "2015-7442"},
+		{"CVE", "2016-7489"},
+		{}
+	}
+};
-- 
2.55.0


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