[LTP] [PATCH 05/33] keyctl13: Test KEYCTL_DESCRIBE size query

[Andrea Cervesato <andrea.cervesato@suse.de>]

From: Andrea Cervesato <andrea.cervesato@suse.com>

Test KEYCTL_DESCRIBE when called with a NULL buffer and buflen 0:
verify the call succeeds and returns the full description length
without writing to userspace memory.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
 runtest/syscalls                            |  1 +
 testcases/kernel/syscalls/keyctl/.gitignore |  1 +
 testcases/kernel/syscalls/keyctl/keyctl13.c | 46 +++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/runtest/syscalls b/runtest/syscalls
index d8e846e65..25367084d 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -730,6 +730,7 @@ keyctl09 keyctl09
 keyctl10 keyctl10
 keyctl11 keyctl11
 keyctl12 keyctl12
+keyctl13 keyctl13
 
 kcmp01 kcmp01
 kcmp02 kcmp02
diff --git a/testcases/kernel/syscalls/keyctl/.gitignore b/testcases/kernel/syscalls/keyctl/.gitignore
index 9ce6e2250..d4ce61a6e 100644
--- a/testcases/kernel/syscalls/keyctl/.gitignore
+++ b/testcases/kernel/syscalls/keyctl/.gitignore
@@ -10,3 +10,4 @@
 /keyctl10
 /keyctl11
 /keyctl12
+/keyctl13
diff --git a/testcases/kernel/syscalls/keyctl/keyctl13.c b/testcases/kernel/syscalls/keyctl/keyctl13.c
new file mode 100644
index 000000000..ebdb3cf32
--- /dev/null
+++ b/testcases/kernel/syscalls/keyctl/keyctl13.c
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Andrea Cervesato <andrea.cervesato@suse.com>
+ */
+
+/*\
+ * Test ``KEYCTL_DESCRIBE`` of :manpage:`keyctl(2)` with NULL buffer and buflen 0.
+ *
+ * [Algorithm]
+ *
+ * - describe a key with NULL buffer and ``buflen = 0``, verify the full length
+ *   is returned without writing
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+
+#include "keyctl_common.h"
+
+static key_serial_t key;
+
+static void setup(void)
+{
+	SAFE_KEYCTL(KEYCTL_JOIN_SESSION_KEYRING, 0, 0, 0, 0);
+
+	key = new_user_key("k", "payload", 7, KEY_SPEC_PROCESS_KEYRING);
+	SAFE_KEYCTL(KEYCTL_SETPERM, key, KEY_PERM_SET, 0, 0);
+}
+
+static void run(void)
+{
+	char expected[64];
+	long expected_len;
+
+	expected_len = snprintf(expected, sizeof(expected),
+				"user;%u;%u;%08x;k",
+				getuid(), getgid(), KEY_PERM_SET) + 1;
+
+	TST_EXP_VAL(keyctl(KEYCTL_DESCRIBE, key, (unsigned long)NULL, 0, 0),
+		    expected_len);
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.test_all = run,
+};

-- 
2.51.0


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