kasan: improve double-free reports

Currently we just dump stack in case of double free bug.
Let's dump all info about the object that we have.

[aryabinin@virtuozzo.com: change double free message per Alexander]
  Link: http://lkml.kernel.org/r/1470153654-30160-1-git-send-email-aryabinin@virtuozzo.com
Link: http://lkml.kernel.org/r/1470062715-14077-6-git-send-email-aryabinin@virtuozzo.com
Signed-off-by: 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>

3 files changed, 41 insertions, 18 deletions

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 92750e3b0083..88af13c00d3c 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -543,8 +543,7 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object)
 
         shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
         if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
-                pr_err("Double free");
-                dump_stack();
+                kasan_report_double_free(cache, object, shadow_byte);
                 return true;
         }
 
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 9b7b31e25fd2..e5c2181fee6f 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -99,6 +99,8 @@ static inline bool kasan_report_enabled(void)
 
 void kasan_report(unsigned long addr, size_t size,
                 bool is_write, unsigned long ip);
+void kasan_report_double_free(struct kmem_cache *cache, void *object,
+                        s8 shadow);
 
 #if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
 void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index f437398b685a..24c1211fe9d5 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -116,6 +116,26 @@ static inline bool init_task_stack_addr(const void *addr)
                         sizeof(init_thread_union.stack));
 }
 
+static DEFINE_SPINLOCK(report_lock);
+
+static void kasan_start_report(unsigned long *flags)
+{
+        /*
+         * Make sure we don't end up in loop.
+         */
+        kasan_disable_current();
+        spin_lock_irqsave(&report_lock, *flags);
+        pr_err("==================================================================\n");
+}
+
+static void kasan_end_report(unsigned long *flags)
+{
+        pr_err("==================================================================\n");
+        add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+        spin_unlock_irqrestore(&report_lock, *flags);
+        kasan_enable_current();
+}
+
 static void print_track(struct kasan_track *track)
 {
         pr_err("PID = %u\n", track->pid);
@@ -129,8 +149,7 @@ static void print_track(struct kasan_track *track)
         }
 }
 
-static void kasan_object_err(struct kmem_cache *cache, struct page *page,
-                                void *object, char *unused_reason)
+static void kasan_object_err(struct kmem_cache *cache, void *object)
 {
         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 
@@ -147,6 +166,18 @@ static void kasan_object_err(struct kmem_cache *cache, struct page *page,
         print_track(&alloc_info->free_track);
 }
 
+void kasan_report_double_free(struct kmem_cache *cache, void *object,
+                        s8 shadow)
+{
+        unsigned long flags;
+
+        kasan_start_report(&flags);
+        pr_err("BUG: Double free or freeing an invalid pointer\n");
+        pr_err("Unexpected shadow byte: 0x%hhX\n", shadow);
+        kasan_object_err(cache, object);
+        kasan_end_report(&flags);
+}
+
 static void print_address_description(struct kasan_access_info *info)
 {
         const void *addr = info->access_addr;
@@ -160,8 +191,7 @@ static void print_address_description(struct kasan_access_info *info)
                         struct kmem_cache *cache = page->slab_cache;
                         object = nearest_obj(cache, page,
                                                 (void *)info->access_addr);
-                        kasan_object_err(cache, page, object,
-                                        "kasan: bad access detected");
+                        kasan_object_err(cache, object);
                         return;
                 }
                 dump_page(page, "kasan: bad access detected");
@@ -226,19 +256,13 @@ static void print_shadow_for_address(const void *addr)
         }
 }
 
-static DEFINE_SPINLOCK(report_lock);
-
 static void kasan_report_error(struct kasan_access_info *info)
 {
         unsigned long flags;
         const char *bug_type;
 
-        /*
-         * Make sure we don't end up in loop.
-         */
-        kasan_disable_current();
-        spin_lock_irqsave(&report_lock, flags);
-        pr_err("==================================================================\n");
+        kasan_start_report(&flags);
+
         if (info->access_addr <
                         kasan_shadow_to_mem((void *)KASAN_SHADOW_START)) {
                 if ((unsigned long)info->access_addr < PAGE_SIZE)
@@ -259,10 +283,8 @@ static void kasan_report_error(struct kasan_access_info *info)
                 print_address_description(info);
                 print_shadow_for_address(info->first_bad_addr);
         }
-        pr_err("==================================================================\n");
-        add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
-        spin_unlock_irqrestore(&report_lock, flags);
-        kasan_enable_current();
+
+        kasan_end_report(&flags);
 }
 
 void kasan_report(unsigned long addr, size_t size,