[LTP] [PATCH v2 04/33] keyctl12: Test KEYCTL_DESCRIBE with too small buffer

[Andrea Cervesato]

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

Test KEYCTL_DESCRIBE when called with a buffer smaller than the
full description length: verify the buffer is left untouched and the
return value still reports the full length.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
 runtest/syscalls                            |  1 +
 testcases/kernel/syscalls/keyctl/.gitignore |  1 +
 testcases/kernel/syscalls/keyctl/keyctl12.c | 62 +++++++++++++++++++++++++++++
 3 files changed, 64 insertions(+)

diff --git a/runtest/syscalls b/runtest/syscalls
index 7c9042471..d8e846e65 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -729,6 +729,7 @@ keyctl08 keyctl08
 keyctl09 keyctl09
 keyctl10 keyctl10
 keyctl11 keyctl11
+keyctl12 keyctl12
 
 kcmp01 kcmp01
 kcmp02 kcmp02
diff --git a/testcases/kernel/syscalls/keyctl/.gitignore b/testcases/kernel/syscalls/keyctl/.gitignore
index 4974fe48d..9ce6e2250 100644
--- a/testcases/kernel/syscalls/keyctl/.gitignore
+++ b/testcases/kernel/syscalls/keyctl/.gitignore
@@ -9,3 +9,4 @@
 /keyctl09
 /keyctl10
 /keyctl11
+/keyctl12
diff --git a/testcases/kernel/syscalls/keyctl/keyctl12.c b/testcases/kernel/syscalls/keyctl/keyctl12.c
new file mode 100644
index 000000000..b135fbe49
--- /dev/null
+++ b/testcases/kernel/syscalls/keyctl/keyctl12.c
@@ -0,0 +1,62 @@
+// 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 too small buffer.
+ *
+ * [Algorithm]
+ *
+ * - describe a key with buffer smaller than full length, verify the buffer
+ *   remains untouched and the return value is unchanged
+ */
+
+#include "keyctl_common.h"
+
+#define BUF_SIZE	64
+
+static key_serial_t key;
+static long desc_len;
+static char buf[BUF_SIZE];
+
+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);
+
+	TEST(keyctl(KEYCTL_DESCRIBE, key, (unsigned long)NULL, 0, 0));
+	if (TST_RET < 0)
+		tst_brk(TBROK | TTERRNO, "KEYCTL_DESCRIBE failed");
+
+	desc_len = TST_RET;
+}
+
+static void run(void)
+{
+	size_t i;
+
+	memset(buf, 0xAA, sizeof(buf));
+	TST_EXP_EQ_LI_SILENT(keyctl(KEYCTL_DESCRIBE, key, (unsigned long)buf,
+				    desc_len - 1, 0), desc_len);
+	if (!TST_PASS)
+		return;
+
+	for (i = 0; i < sizeof(buf); i++) {
+		if (buf[i] != (char)0xAA) {
+			tst_res(TFAIL,
+				"too small buffer was written to at offset %zu",
+				i);
+			return;
+		}
+	}
+
+	tst_res(TPASS, "too small buffer was left untouched");
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.test_all = run,
+};

-- 
2.51.0