kasan: fix quarantine conflicting with init_on_free

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: 1be4a323b51f ("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>

diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index d8ccff4c1275ec7a7f8081141c2baee8e4798af2..47ed4fc33a29e094070fcfab9947b2f59434059e 100644 (file)
--- 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         * free track is no longer valid.