futex_cmp_requeue03: Add EFAULT error coverage test

futex(FUTEX_CMP_REQUEUE) has no existing test for EFAULT. Add coverage
for the cases where uaddr or uaddr2 points to unmapped or inaccessible
(PROT_NONE) memory.

Signed-off-by: Michael Menasherov <mmenashe@redhat.com>

Author: AshWizard

runtest/syscalls

@@ -1863,6 +1863,7 @@ perf_event_open02 perf_event_open02
 
 futex_cmp_requeue01 futex_cmp_requeue01
 futex_cmp_requeue02 futex_cmp_requeue02
+futex_cmp_requeue03 futex_cmp_requeue03
 futex_wait01 futex_wait01
 futex_wait02 futex_wait02
 futex_wait03 futex_wait03

testcases/kernel/syscalls/futex/.gitignore

@@ -16,3 +16,4 @@
 /futex_wait06
 /futex_wait07
 /futex_wake05
+/futex_cmp_requeue03

testcases/kernel/syscalls/futex/futex_cmp_requeue03.c

@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2026 Red Hat, Inc.
+ * Copyright (C) 2026 Michael Menasherov <mmenashe@redhat.com>
+ */
+
+/*\
+ * Check that futex(FUTEX_CMP_REQUEUE) returns EFAULT when uaddr or
+ * uaddr2 points to unmapped memory, or when uaddr points to memory
+ * without read permission (PROT_NONE).
+ *
+ * get_futex_key() is called for both uaddr and uaddr2 before the
+ * *uaddr == val check; futex_var and val are both FUTEX_INITIALIZER.
+ */
+
+#include <errno.h>
+#include <sys/mman.h>
+
+#include "futextest.h"
+
+static futex_t futex_var = FUTEX_INITIALIZER;
+static futex_t *futex_ptr = &futex_var;
+static futex_t *unmapped_addr;
+static futex_t *prot_none_addr;
+
+static struct futex_test_variants variants[] = {
+#if (__NR_futex != __LTP__NR_INVALID_SYSCALL)
+	{ .fntype = FUTEX_FN_FUTEX, .desc = "syscall with old kernel spec"},
+#endif
+
+#if (__NR_futex_time64 != __LTP__NR_INVALID_SYSCALL)
+	{ .fntype = FUTEX_FN_FUTEX64, .desc = "syscall time64 with kernel spec"},
+#endif
+};
+
+static struct testcase {
+	const char *desc;
+	futex_t **uaddr;
+	futex_t **uaddr2;
+	int exp_errno;
+} testcases[] = {
+	{
+		.desc = "uaddr unmapped",
+		.uaddr = &unmapped_addr,
+		.uaddr2 = &futex_ptr,
+		.exp_errno = EFAULT,
+	},
+	{
+		.desc = "uaddr2 unmapped",
+		.uaddr = &futex_ptr,
+		.uaddr2 = &unmapped_addr,
+		.exp_errno = EFAULT,
+	},
+	{
+		.desc = "uaddr PROT_NONE",
+		.uaddr = &prot_none_addr,
+		.uaddr2 = &futex_ptr,
+		.exp_errno = EFAULT,
+	},
+};
+
+static void run(unsigned int n)
+{
+	struct futex_test_variants *tv = &variants[tst_variant];
+	struct testcase *tc = &testcases[n];
+
+	TST_EXP_FAIL(futex_cmp_requeue(tv->fntype, *tc->uaddr, futex_var,
+				       *tc->uaddr2, 1, 1, 0), tc->exp_errno, "%s", tc->desc);
+}
+
+static void setup(void)
+{
+	struct futex_test_variants *tv = &variants[tst_variant];
+	size_t pagesize = getpagesize();
+
+	tst_res(TINFO, "Testing variant: %s", tv->desc);
+	futex_supported_by_kernel(tv->fntype);
+
+	unmapped_addr = SAFE_MMAP(NULL, pagesize, PROT_READ | PROT_WRITE,
+				  MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	SAFE_MUNMAP((void *)unmapped_addr, pagesize);
+
+	prot_none_addr = SAFE_MMAP(NULL, pagesize, PROT_NONE,
+				   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+}
+
+static void cleanup(void)
+{
+	if (prot_none_addr)
+		SAFE_MUNMAP((void *)prot_none_addr, getpagesize());
+}
+
+static struct tst_test test = {
+	.setup = setup,
+	.cleanup = cleanup,
+	.test = run,
+	.tcnt = ARRAY_SIZE(testcases),
+	.test_variants = ARRAY_SIZE(variants),
+};