linux-kernel - [PATCH 5.15 101/135] selftest/vm: verify remap destination address in mremap

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Date:   Tue, 10 May 2022 15:08:03 +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 5.15 101/135] selftest/vm: verify remap destination address in mremap_test

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

[ Upstream commit 18d609daa546c919fd36b62a7b510c18de4b4af8 ]

Because mremap does not have a MAP_FIXED_NOREPLACE flag, it can destroy
existing mappings.  This causes a segfault when regions such as text are
remapped and the permissions are changed.

Verify the requested mremap destination address does not overlap any
existing mappings by using mmap's MAP_FIXED_NOREPLACE flag.  Keep
incrementing the destination address until a valid mapping is found or
fail the current test once the max address is reached.

Link: https://lkml.kernel.org/r/20220420215721.4868-2-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 | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/tools/testing/selftests/vm/mremap_test.c b/tools/testing/selftests/vm/mremap_test.c
index efcbf537b3d5..8f4dbbd60c09 100644
--- a/tools/testing/selftests/vm/mremap_test.c
+++ b/tools/testing/selftests/vm/mremap_test.c
@@ -66,6 +66,30 @@ enum {
 	.expect_failure = should_fail				\
 }
 
+/*
+ * Returns false if the requested remap region overlaps with an
+ * existing mapping (e.g text, stack) else returns true.
+ */
+static bool is_remap_region_valid(void *addr, unsigned long long size)
+{
+	void *remap_addr = NULL;
+	bool ret = true;
+
+	/* Use MAP_FIXED_NOREPLACE flag to ensure region is not mapped */
+	remap_addr = mmap(addr, size, PROT_READ | PROT_WRITE,
+					 MAP_FIXED_NOREPLACE | MAP_ANONYMOUS | MAP_SHARED,
+					 -1, 0);
+
+	if (remap_addr == MAP_FAILED) {
+		if (errno == EEXIST)
+			ret = false;
+	} else {
+		munmap(remap_addr, size);
+	}
+
+	return ret;
+}
+
 /* Returns mmap_min_addr sysctl tunable from procfs */
 static unsigned long long get_mmap_min_addr(void)
 {
-- 
2.35.1