[PATCH v3 7/7] mremap09: Add test for expanding over unmapped gap

From: Andrea Cervesato <andrea.cervesato-IBi9RG/[email protected]>

Add a test case for mremap() without MREMAP_MAYMOVE where we map
three pages, unmap the middle one to create a hole, and then
attempt to expand the first page to cover all three. The mremap()
call must fail with ENOMEM since the third page is occupied.

Signed-off-by: Andrea Cervesato <andrea.cervesato-IBi9RG/[email protected]>
---
 runtest/syscalls                            |  1 +
 testcases/kernel/syscalls/mremap/.gitignore |  1 +
 testcases/kernel/syscalls/mremap/mremap09.c | 59 +++++++++++++++++++++++++++++
 3 files changed, 61 insertions(+)

diff --git a/runtest/syscalls b/runtest/syscalls
index ede795a48..5166886c4 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -947,6 +947,7 @@ mremap05 mremap05
 mremap06 mremap06
 mremap07 mremap07
 mremap08 mremap08
+mremap09 mremap09
 
 mseal01 mseal01
 mseal02 mseal02
diff --git a/testcases/kernel/syscalls/mremap/.gitignore b/testcases/kernel/syscalls/mremap/.gitignore
index dd4bf4e8e..a7ae3b643 100644
--- a/testcases/kernel/syscalls/mremap/.gitignore
+++ b/testcases/kernel/syscalls/mremap/.gitignore
@@ -6,3 +6,4 @@
 /mremap06
 /mremap07
 /mremap08
+/mremap09
diff --git a/testcases/kernel/syscalls/mremap/mremap09.c b/testcases/kernel/syscalls/mremap/mremap09.c
new file mode 100644
index 000000000..28ab9e310
--- /dev/null
+++ b/testcases/kernel/syscalls/mremap/mremap09.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Linux Test Project
+ */
+
+/*\
+ * Verify that :manpage:`mremap(2)` fails with errno ``ENOMEM`` when it is used
+ * to expand an existing mapping in place, if the region cannot be expanded at
+ * the current virtual address and the ``MREMAP_MAYMOVE`` flag is not set.
+ *
+ * [Algorithm]
+ *
+ * - map an anonymous region of three pages
+ * - unmap the middle page to create a gap
+ * - call mremap() on the first page to grow it to three pages with ``flags``
+ *   set to 0
+ * - expect the call to fail with ``MAP_FAILED`` and ``ENOMEM`` since the
+ *   third page is occupied.
+ */
+
+#define _GNU_SOURCE
+#include <sys/mman.h>
+#include "tst_test.h"
+
+static size_t pagesize;
+static void *addr = MAP_FAILED;
+
+static void setup(void)
+{
+	pagesize = getpagesize();
+}
+
+static void run(void)
+{
+	size_t map_size = 3 * pagesize;
+	size_t old_size = 1 * pagesize;
+	size_t new_size = 3 * pagesize;
+
+	addr = SAFE_MMAP(NULL, map_size, PROT_READ | PROT_WRITE,
+			 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+	/* unmap the middle page to create a gap */
+	SAFE_MUNMAP((char *)addr + pagesize, pagesize);
+
+	TST_EXP_FAIL_PTR_VOID(mremap(addr, old_size, new_size, 0), ENOMEM);
+
+	if (TST_RET_PTR != MAP_FAILED) {
+		SAFE_MUNMAP(TST_RET_PTR, new_size);
+		return;
+	}
+
+	SAFE_MUNMAP(addr, pagesize);
+	SAFE_MUNMAP((char *)addr + 2 * pagesize, pagesize);
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.test_all = run,
+};

-- 
2.51.0


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