linux-kernel - [PATCH 5.17 119/140] selftest/vm: verify mmap addr in mremap

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Date:   Tue, 10 May 2022 15:08:29 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.17 119/140] selftest/vm: verify mmap addr in mremap_test

From: Sidhartha Kumar <sidhartha.kumar@...cle.com>

[ Upstream commit 9c85a9bae267f6b5e5e374d0d023bbbe9db096d3 ]

Avoid calling mmap with requested addresses that are less than the
system's mmap_min_addr.  When run as root, mmap returns EACCES when
trying to map addresses < mmap_min_addr.  This is not one of the error
codes for the condition to retry the mmap in the test.

Rather than arbitrarily retrying on EACCES, don't attempt an mmap until
addr > vm.mmap_min_addr.

Add a munmap call after an alignment check as the mappings are retained
after the retry and can reach the vm.max_map_count sysctl.

Link: https://lkml.kernel.org/r/20220420215721.4868-1-sidhartha.kumar@oracle.com
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/testing/selftests/vm/mremap_test.c | 29 ++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/testing/selftests/vm/mremap_test.c b/tools/testing/selftests/vm/mremap_test.c
index 58775dab3cc6..380a4593dbd6 100644
--- a/tools/testing/selftests/vm/mremap_test.c
+++ b/tools/testing/selftests/vm/mremap_test.c
@@ -65,6 +65,35 @@ enum {
 	.expect_failure = should_fail				\
 }
 
+/* Returns mmap_min_addr sysctl tunable from procfs */
+static unsigned long long get_mmap_min_addr(void)
+{
+	FILE *fp;
+	int n_matched;
+	static unsigned long long addr;
+
+	if (addr)
+		return addr;
+
+	fp = fopen("/proc/sys/vm/mmap_min_addr", "r");
+	if (fp == NULL) {
+		ksft_print_msg("Failed to open /proc/sys/vm/mmap_min_addr: %s\n",
+			strerror(errno));
+		exit(KSFT_SKIP);
+	}
+
+	n_matched = fscanf(fp, "%llu", &addr);
+	if (n_matched != 1) {
+		ksft_print_msg("Failed to read /proc/sys/vm/mmap_min_addr: %s\n",
+			strerror(errno));
+		fclose(fp);
+		exit(KSFT_SKIP);
+	}
+
+	fclose(fp);
+	return addr;
+}
+
 /*
  * Returns false if the requested remap region overlaps with an
  * existing mapping (e.g text, stack) else returns true.
-- 
2.35.1