kasan, slub: fix more conflicts with CONFIG_SLAB_FREELIST_HARDENED

When CONFIG_KASAN_SW_TAGS is enabled, ptr_addr might be tagged.  Normally,
this doesn't cause any issues, as both set_freepointer() and
get_freepointer() are called with a pointer with the same tag.  However,
there are some issues with CONFIG_SLUB_DEBUG code.  For example, when
__free_slub() iterates over objects in a cache, it passes untagged
pointers to check_object().  check_object() in turns calls
get_freepointer() with an untagged pointer, which causes the freepointer
to be restored incorrectly.

Add kasan_reset_tag to freelist_ptr(). Also add a detailed comment.

Link: http://lkml.kernel.org/r/bf858f26ef32eb7bd24c665755b3aee4bc58d0e4.1550103861.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reported-by: Qian Cai <cai@lca.pw>
Tested-by: Qian Cai <cai@lca.pw>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slub.c b/mm/slub.c
index 80da3a4..c80e669 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -249,7 +249,18 @@ static inline void *freelist_ptr(const struct kmem_cache *s, void *ptr,
                                 unsigned long ptr_addr)
 {
 #ifdef CONFIG_SLAB_FREELIST_HARDENED
-       return (void *)((unsigned long)ptr ^ s->random ^ ptr_addr);
+       /*
+        * When CONFIG_KASAN_SW_TAGS is enabled, ptr_addr might be tagged.
+        * Normally, this doesn't cause any issues, as both set_freepointer()
+        * and get_freepointer() are called with a pointer with the same tag.
+        * However, there are some issues with CONFIG_SLUB_DEBUG code. For
+        * example, when __free_slub() iterates over objects in a cache, it
+        * passes untagged pointers to check_object(). check_object() in turns
+        * calls get_freepointer() with an untagged pointer, which causes the
+        * freepointer to be restored incorrectly.
+        */
+       return (void *)((unsigned long)ptr ^ s->random ^
+                       (unsigned long)kasan_reset_tag((void *)ptr_addr));
 #else
        return ptr;
 #endif