[LTP] [PATCH v12 0/3] open16: allow restricted O_CREAT of FIFOs and regular files

[LTP] [PATCH v12 0/3] open16: allow restricted O_CREAT of FIFOs and regular files

[Wei Gao via ltp]

v11->v12:
- Restructured the series into three clean commits

Wei Gao (3):
  lib/tst_uid: Remove spurious TERRNO from tst_get_free_gid success path
  lib: New library function tst_get_free_uid
  open16: allow restricted O_CREAT of FIFOs and regular files

 include/tst_uid.h                         |  29 ++++-
 lib/tst_uid.c                             |  30 ++++-
 runtest/syscalls                          |   1 +
 testcases/kernel/syscalls/open/.gitignore |   1 +
 testcases/kernel/syscalls/open/open16.c   | 135 ++++++++++++++++++++++
 5 files changed, 191 insertions(+), 5 deletions(-)
 create mode 100644 testcases/kernel/syscalls/open/open16.c

-- 
2.54.0


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[LTP] [PATCH v12 1/3] lib/tst_uid: Remove spurious TERRNO from tst_get_free_gid success path

[Wei Gao via ltp]

tst_get_free_gid_() prints the found GID when it succeeds, but it
incorrectly includes TERRNO in tst_res_(). This prints whatever value
happens to be in errno (often 0 or a stale value) which is confusing in
a success path.

Remove the spurious TERRNO flag from the tst_res_() success message.

Signed-off-by: Wei Gao <wegao@suse.com>
---
 lib/tst_uid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/tst_uid.c b/lib/tst_uid.c
index af4ef8cf7..b0b087362 100644
--- a/lib/tst_uid.c
+++ b/lib/tst_uid.c
@@ -24,7 +24,7 @@ gid_t tst_get_free_gid_(const char *file, const int lineno, gid_t skip)
 			continue;
 
 		if (errno == 0 || errno == ENOENT || errno == ESRCH) {
-			tst_res_(file, lineno, TINFO | TERRNO,
+			tst_res_(file, lineno, TINFO,
 				"Found unused GID %d", (int)ret);
 			return ret;
 		}
-- 
2.54.0


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Re: [LTP] lib/tst_uid: Remove spurious TERRNO from tst_get_free_gid success path

[linuxtestproject.agent]

Hi Wei,

On Wed, 22 Jul 2026, Wei Gao wrote:
> lib/tst_uid: Remove spurious TERRNO from tst_get_free_gid success path

Verdict - Reviewed

---
Note:

The agent can sometimes produce false positives although often its
findings are genuine. If you find issues with the review, please
comment this email or ignore the suggestions.

Regards,
LTP AI Reviewer

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[LTP] [PATCH v12 2/3] lib: New library function tst_get_free_uid

[Wei Gao via ltp]

Add tst_get_free_uid() to dynamically find unused UIDs for tests.

Some tests need a completely unassigned, unused UID. This is used by
open16 to verify restricted O_CREAT in sticky directories by running
as a sandboxed user with no file ownership or privileges.

Signed-off-by: Wei Gao <wegao@suse.com>
---
 include/tst_uid.h | 29 +++++++++++++++++++++++++----
 lib/tst_uid.c     | 28 ++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/include/tst_uid.h b/include/tst_uid.h
index 2237ddcbf..c73450956 100644
--- a/include/tst_uid.h
+++ b/include/tst_uid.h
@@ -7,12 +7,33 @@
 
 #include <sys/types.h>
 
-/*
- * Find unassigned gid. The skip argument can be used to ignore e.g. the main
- * group of a specific user in case it's not listed in the group file. If you
- * do not need to skip any specific gid, simply set it to 0.
+uid_t tst_get_free_uid_(const char *file, const int lineno, uid_t skip);
+
+/**
+ * tst_get_free_uid() - Find a UID not assigned to any user.
+ * @skip: UID value to skip (pass 0 to skip none).
+ *
+ * Scans the password database for the first unused UID starting
+ * from 1, skipping @skip. Calls tst_brk(TBROK) if no free UID
+ * is found or a lookup error occurs.
+ *
+ * Return: An unused uid_t value.
  */
+#define tst_get_free_uid(skip) tst_get_free_uid_(__FILE__, __LINE__, (skip))
+
 gid_t tst_get_free_gid_(const char *file, const int lineno, gid_t skip);
+
+/**
+ * tst_get_free_gid() - Find a GID not assigned to any group.
+ * @skip: GID value to skip (pass 0 to skip none).
+ *
+ * Scans the group database for the first unused GID starting from 1,
+ * skipping @skip. The @skip argument can be used to ignore e.g. the main
+ * group of a specific user in case it's not listed in the group file.
+ * Calls tst_brk(TBROK) if no free GID is found or a lookup error occurs.
+ *
+ * Return: An unused gid_t value.
+ */
 #define tst_get_free_gid(skip) tst_get_free_gid_(__FILE__, __LINE__, (skip))
 
 /*
diff --git a/lib/tst_uid.c b/lib/tst_uid.c
index b0b087362..47c267bc4 100644
--- a/lib/tst_uid.c
+++ b/lib/tst_uid.c
@@ -5,6 +5,7 @@
 
 #include <sys/types.h>
 #include <grp.h>
+#include <pwd.h>
 #include <errno.h>
 
 #define TST_NO_DEFAULT_MAIN
@@ -12,6 +13,33 @@
 #include "tst_uid.h"
 
 #define MAX_GID 32767
+#define MAX_UID 32767
+
+uid_t tst_get_free_uid_(const char *file, const int lineno, uid_t skip)
+{
+	uid_t ret;
+
+	for (ret = 1; ret < MAX_UID; ret++) {
+		if (ret == skip)
+			continue;
+
+		errno = 0;
+		if (getpwuid(ret))
+			continue;
+
+		if (errno == 0 || errno == ENOENT || errno == ESRCH) {
+			tst_res_(file, lineno, TINFO,
+				"Found unused UID %d", (int)ret);
+			return ret;
+		}
+
+		tst_brk_(file, lineno, TBROK | TERRNO, "User ID lookup failed");
+		return (uid_t)-1;
+	}
+
+	tst_brk_(file, lineno, TBROK, "No free user ID found");
+	return (uid_t)-1;
+}
 
 gid_t tst_get_free_gid_(const char *file, const int lineno, gid_t skip)
 {
-- 
2.54.0


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[LTP] [PATCH v12 3/3] open16: allow restricted O_CREAT of FIFOs and regular files

[Wei Gao via ltp]

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
(Level 1 and Level 2 protections) 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>
---
 runtest/syscalls                          |   1 +
 testcases/kernel/syscalls/open/.gitignore |   1 +
 testcases/kernel/syscalls/open/open16.c   | 135 ++++++++++++++++++++++
 3 files changed, 137 insertions(+)
 create mode 100644 testcases/kernel/syscalls/open/open16.c

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..c74601032
--- /dev/null
+++ b/testcases/kernel/syscalls/open/open16.c
@@ -0,0 +1,135 @@
+// 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 test covers the positive
+ * case where access is allowed when protection is disabled (level 0), and the
+ * negative cases where access is disallowed (EACCES) in world-writable (level
+ * 1) or group-writable (level 2) sticky directories when the file is not owned
+ * by the opener.
+ *
+ * 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 PROTECTED_REGULAR "/proc/sys/fs/protected_regular"
+#define PROTECTED_FIFOS "/proc/sys/fs/protected_fifos"
+#define TEST_FIFO_PATH DIR "/" TEST_FIFO
+
+static int dir_fd = -1;
+static uid_t uid1, uid2;
+static gid_t gid1;
+
+static struct tcase {
+	char *level;
+	int exp_errno;
+	uid_t owner_uid;
+	int use_nobody_gid;
+	mode_t dir_mode;
+} tcases[] = {
+	{"0", 0,      0,  0, 0777 | S_ISVTX},
+	{"1", EACCES, 0,  0, 0777 | S_ISVTX},
+	{"2", EACCES, -1, 1, 0030 | S_ISVTX},
+};
+
+static void verify_open(unsigned int n)
+{
+	struct tcase *tc = &tcases[n];
+	pid_t pid;
+
+	SAFE_FILE_PRINTF(PROTECTED_REGULAR, "%s", tc->level);
+	SAFE_FILE_PRINTF(PROTECTED_FIFOS, "%s", tc->level);
+
+	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);
+
+	pid = SAFE_FORK();
+	if (!pid) {
+		SAFE_SETGID(gid1);
+		SAFE_SETUID(uid2);
+
+		if (tc->exp_errno) {
+			TST_EXP_FAIL2(openat(dir_fd, TEST_FILE, O_RDWR | O_CREAT, 0777),
+				      tc->exp_errno, "openat %s (Level %s)", TEST_FILE, tc->level);
+			TST_EXP_FAIL2(open(TEST_FIFO_PATH, O_RDWR | O_CREAT, 0777),
+				      tc->exp_errno, "open %s (Level %s)", TEST_FIFO, tc->level);
+		} else {
+			int fd = TST_EXP_FD(openat(dir_fd, TEST_FILE, O_CREAT | O_RDWR, 0777));
+
+			if (TST_PASS)
+				SAFE_CLOSE(fd);
+
+			fd = TST_EXP_FD(open(TEST_FIFO_PATH, O_RDWR | O_CREAT, 0777));
+			if (TST_PASS)
+				SAFE_CLOSE(fd);
+		}
+
+		exit(0);
+	}
+
+	SAFE_WAITPID(pid, NULL, 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[]) {
+		{PROTECTED_REGULAR, NULL, TST_SR_TCONF},
+		{PROTECTED_FIFOS, NULL, TST_SR_TCONF},
+		{}
+	},
+	.tags = (const struct tst_tag[]) {
+		{"linux-git", "30aba6656f61"},
+		{}
+	}
+};
-- 
2.54.0


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