[LTP] [PATCH v2 30/33] keyctl36: Test KEYCTL_CAPABILITIES buffer sizing

[Andrea Cervesato]

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

Test KEYCTL_CAPABILITIES with short buffer (verifying partial copy
without overrun) and oversized buffer (verifying trailing space is
zero-filled while returning the full capability length).

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
 runtest/syscalls                            |  1 +
 testcases/kernel/syscalls/keyctl/.gitignore |  1 +
 testcases/kernel/syscalls/keyctl/keyctl36.c | 88 +++++++++++++++++++++++++++++
 3 files changed, 90 insertions(+)

diff --git a/runtest/syscalls b/runtest/syscalls
index 67d626c22..8ad8f0fe5 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -753,6 +753,7 @@ keyctl32 keyctl32
 keyctl33 keyctl33
 keyctl34 keyctl34
 keyctl35 keyctl35
+keyctl36 keyctl36
 
 kcmp01 kcmp01
 kcmp02 kcmp02
diff --git a/testcases/kernel/syscalls/keyctl/.gitignore b/testcases/kernel/syscalls/keyctl/.gitignore
index 58ebb452f..a4da8ae80 100644
--- a/testcases/kernel/syscalls/keyctl/.gitignore
+++ b/testcases/kernel/syscalls/keyctl/.gitignore
@@ -33,3 +33,4 @@
 /keyctl33
 /keyctl34
 /keyctl35
+/keyctl36
diff --git a/testcases/kernel/syscalls/keyctl/keyctl36.c b/testcases/kernel/syscalls/keyctl/keyctl36.c
new file mode 100644
index 000000000..58fa56a07
--- /dev/null
+++ b/testcases/kernel/syscalls/keyctl/keyctl36.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Andrea Cervesato <andrea.cervesato@suse.com>
+ */
+
+/*\
+ * Test ``KEYCTL_CAPABILITIES`` buffer sizing and padding of :manpage:`keyctl(2)`.
+ *
+ * [Algorithm]
+ *
+ * - verify a 1-byte buffer receives 1 byte while the full size is returned
+ *   and canary bytes beyond 1 byte remain untouched
+ * - verify an oversized buffer is zero-filled beyond the capability size
+ */
+
+#include "keyctl_common.h"
+
+#define CANARY		0xaa
+#define OVERSIZE	16
+
+static long caps_len;
+static unsigned char short_buf[4];
+static unsigned char large_buf[OVERSIZE];
+
+static void setup(void)
+{
+	TEST(keyctl(KEYCTL_CAPABILITIES, (unsigned long)NULL, 0, 0, 0));
+	if (TST_RET < 0)
+		tst_brk(TBROK | TTERRNO, "KEYCTL_CAPABILITIES size query failed");
+
+	caps_len = TST_RET;
+}
+
+static void run(void)
+{
+	size_t i;
+	int zero_padded = 1;
+
+	memset(short_buf, CANARY, sizeof(short_buf));
+	TST_EXP_EQ_LI_SILENT(keyctl(KEYCTL_CAPABILITIES,
+				    (unsigned long)short_buf, 1, 0, 0),
+			     caps_len);
+	if (!TST_PASS)
+		return;
+
+	if (short_buf[0] == CANARY) {
+		tst_res(TFAIL, "short buffer was not populated");
+		return;
+	}
+
+	for (i = 1; i < sizeof(short_buf); i++) {
+		if (short_buf[i] != CANARY) {
+			tst_res(TFAIL, "copy overran short buffer at offset %zu", i);
+			return;
+		}
+	}
+
+	tst_res(TPASS, "short buffer copied 1 byte without overrun");
+
+	memset(large_buf, CANARY, sizeof(large_buf));
+	TST_EXP_EQ_LI_SILENT(keyctl(KEYCTL_CAPABILITIES,
+				    (unsigned long)large_buf, sizeof(large_buf), 0, 0),
+			     caps_len);
+	if (!TST_PASS)
+		return;
+
+	for (i = caps_len; i < sizeof(large_buf); i++) {
+		if (large_buf[i] != 0) {
+			zero_padded = 0;
+			break;
+		}
+	}
+
+	if (!zero_padded)
+		tst_res(TFAIL, "oversized buffer was not zero-filled at offset %zu", i);
+	else
+		tst_res(TPASS, "oversized buffer zero-filled trailing space");
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.test_all = run,
+	.min_kver = "5.3",
+	.needs_kconfigs = (const char *[]) {
+		"CONFIG_KEYS=y",
+		NULL
+	},
+};

-- 
2.51.0