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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Andrey Konovalov <andreyknvl@google.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.16 0830/1039] kasan: fix quarantine conflicting with init_on_free
Date:   Mon, 24 Jan 2022 19:43:39 +0100
Message-Id: <20220124184153.183232888@linuxfoundation.org>
In-Reply-To: <20220124184125.121143506@linuxfoundation.org>
References: <20220124184125.121143506@linuxfoundation.org>
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From: Andrey Konovalov <andreyknvl@google.com>

[ Upstream commit 26dca996ea7b1ac7008b6b6063fc88b849e3ac3e ]

KASAN's quarantine might save its metadata inside freed objects.  As
this happens after the memory is zeroed by the slab allocator when
init_on_free is enabled, the memory coming out of quarantine is not
properly zeroed.

This causes lib/test_meminit.c tests to fail with Generic KASAN.

Zero the metadata when the object is removed from quarantine.

Link: https://lkml.kernel.org/r/2805da5df4b57138fdacd671f5d227d58950ba54.1640037083.git.andreyknvl@google.com
Fixes: 6471384af2a6 ("mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/kasan/quarantine.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index d8ccff4c1275e..47ed4fc33a29e 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -132,11 +132,22 @@ static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
 static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
 {
 	void *object = qlink_to_object(qlink, cache);
+	struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
 	unsigned long flags;
 
 	if (IS_ENABLED(CONFIG_SLAB))
 		local_irq_save(flags);
 
+	/*
+	 * If init_on_free is enabled and KASAN's free metadata is stored in
+	 * the object, zero the metadata. Otherwise, the object's memory will
+	 * not be properly zeroed, as KASAN saves the metadata after the slab
+	 * allocator zeroes the object.
+	 */
+	if (slab_want_init_on_free(cache) &&
+	    cache->kasan_info.free_meta_offset == 0)
+		memzero_explicit(meta, sizeof(*meta));
+
 	/*
 	 * As the object now gets freed from the quarantine, assume that its
 	 * free track is no longer valid.
-- 
2.34.1