Re: use-after-free in __perf_install_in_context

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Dec 07, 2015 at 05:09:21PM +0100, Dmitry Vyukov wrote:
> If your audit does not give any results, can you give me a patch that
> prints rcu callback submission stacks in KASAN reports?

Just because my brain is fried for today, I figured I'd give it a go.

Completely untested..

---
 include/linux/slub_def.h |  2 ++
 kernel/rcu/tree_plugin.h |  1 +
 mm/slub.c                | 34 ++++++++++++++++++++++++++++++++--
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 33885118523c..445b586c0bfa 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -129,4 +129,6 @@ static inline void *virt_to_obj(struct kmem_cache *s,
 void object_err(struct kmem_cache *s, struct page *page,
 		u8 *object, char *reason);
 
+void object_set_indirect(const void *addr);
+
 #endif /* _LINUX_SLUB_DEF_H */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 630c19772630..4e1e79e01e34 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -659,6 +659,7 @@ static void rcu_preempt_do_callbacks(void)
  */
 void call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
+	object_set_indirect(head);
 	__call_rcu(head, func, rcu_state_p, -1, 0);
 }
 EXPORT_SYMBOL_GPL(call_rcu);
diff --git a/mm/slub.c b/mm/slub.c
index 46997517406e..6977dc7cffcd 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -196,7 +196,12 @@ struct track {
 	unsigned long when;	/* When did the operation occur */
 };
 
-enum track_item { TRACK_ALLOC, TRACK_FREE };
+enum track_item {
+	TRACK_ALLOC = 0,
+	TRACK_FREE,
+	TRACK_INDIRECT,
+	TRACK_NR,
+};
 
 #ifdef CONFIG_SYSFS
 static int sysfs_slab_add(struct kmem_cache *);
@@ -551,6 +556,7 @@ static void init_tracking(struct kmem_cache *s, void *object)
 
 	set_track(s, object, TRACK_FREE, 0UL);
 	set_track(s, object, TRACK_ALLOC, 0UL);
+	set_track(s, object, TRACK_INDIRECT, 0UL);
 }
 
 static void print_track(const char *s, struct track *t)
@@ -579,6 +585,7 @@ static void print_tracking(struct kmem_cache *s, void *object)
 
 	print_track("Allocated", get_track(s, object, TRACK_ALLOC));
 	print_track("Freed", get_track(s, object, TRACK_FREE));
+	print_track("Indirect", get_track(s, object, TRACK_INDIRECT));
 }
 
 static void print_page_info(struct page *page)
@@ -652,6 +659,29 @@ static void print_trailer(struct kmem_cache *s, struct page *page, u8 *p)
 	dump_stack();
 }
 
+void object_set_indirect(const void *addr)
+{
+	if ((addr >= (void *)PAGE_OFFSET) &&
+		(addr < high_memory)) {
+		struct page *page = virt_to_head_page(addr);
+
+		if (PageSlab(page)) {
+			void *object;
+			struct kmem_cache *cache = page->slab_cache;
+			void *last_object;
+
+			object = virt_to_obj(cache, page_address(page), addr);
+			last_object = page_address(page) +
+				page->objects * cache->size;
+
+			if (unlikely(object > last_object))
+				object = last_object; /* we hit into padding */
+
+			set_track(cache, object, TRACK_INDIRECT, (unsigned long)addr);
+		}
+	}
+}
+
 void object_err(struct kmem_cache *s, struct page *page,
 			u8 *object, char *reason)
 {
@@ -767,7 +797,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct page *page, u8 *p)
 
 	if (s->flags & SLAB_STORE_USER)
 		/* We also have user information there */
-		off += 2 * sizeof(struct track);
+		off += TRACK_NR * sizeof(struct track);
 
 	if (s->size == off)
 		return 1;