kasan: handle concurrent kasan_record_aux_stack calls

kasan_record_aux_stack can be called concurrently on the same object.
This might lead to a race condition when rotating the saved aux stack
trace handles, which in turns leads to incorrect accounting of stack depot
handles and refcount underflows in the stack depot code.

Fix by introducing a raw spinlock to protect the aux stack trace handles
in kasan_record_aux_stack.

Link: https://lkml.kernel.org/r/1606b960e2f746862d1f459515972f9695bf448a.1703020707.git.andreyknvl@google.com
Fixes: 773688a6cb24 ("kasan: use stack_depot_put for Generic mode")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Reported-by: syzbot+186b55175d8360728234@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000784b1c060b0074a2@google.com/
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 54e20b2bc3e15e8b2de7e1724b24cd02b705eb98..55e6b5db2cae63604061cc5c5a30a91eafaa8a6a 100644 (file)
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -25,6 +25,7 @@
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 #include <linux/stackdepot.h>
 #include <linux/stacktrace.h>
 #include <linux/string.h>
@@ -471,8 +472,18 @@ void kasan_init_object_meta(struct kmem_cache *cache, const void *object)
        struct kasan_free_meta *free_meta;
 
        alloc_meta = kasan_get_alloc_meta(cache, object);
-       if (alloc_meta)
+       if (alloc_meta) {
                __memset(alloc_meta, 0, sizeof(*alloc_meta));
+
+               /*
+                * Temporarily disable KASAN bug reporting to allow instrumented
+                * raw_spin_lock_init to access aux_lock, which resides inside
+                * of a redzone.
+                */
+               kasan_disable_current();
+               raw_spin_lock_init(&alloc_meta->aux_lock);
+               kasan_enable_current();
+       }
        free_meta = kasan_get_free_meta(cache, object);
        if (free_meta)
                __memset(free_meta, 0, sizeof(*free_meta));
@@ -502,6 +513,8 @@ static void __kasan_record_aux_stack(void *addr, depot_flags_t depot_flags)
        struct kmem_cache *cache;
        struct kasan_alloc_meta *alloc_meta;
        void *object;
+       depot_stack_handle_t new_handle, old_handle;
+       unsigned long flags;
 
        if (is_kfence_address(addr) || !slab)
                return;
@@ -512,9 +525,22 @@ static void __kasan_record_aux_stack(void *addr, depot_flags_t depot_flags)
        if (!alloc_meta)
                return;
 
-       stack_depot_put(alloc_meta->aux_stack[1]);
+       new_handle = kasan_save_stack(0, depot_flags);
+
+       /*
+        * Temporarily disable KASAN bug reporting to allow instrumented
+        * spinlock functions to access aux_lock, which resides inside of a
+        * redzone.
+        */
+       kasan_disable_current();
+       raw_spin_lock_irqsave(&alloc_meta->aux_lock, flags);
+       old_handle = alloc_meta->aux_stack[1];
        alloc_meta->aux_stack[1] = alloc_meta->aux_stack[0];
-       alloc_meta->aux_stack[0] = kasan_save_stack(0, depot_flags);
+       alloc_meta->aux_stack[0] = new_handle;
+       raw_spin_unlock_irqrestore(&alloc_meta->aux_lock, flags);
+       kasan_enable_current();
+
+       stack_depot_put(old_handle);
 }
 
 void kasan_record_aux_stack(void *addr)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 5e298e3ac90945571d04815c7764634b164d7d6e..69e4f5e58e334970ea6b576445ca8899837e0fc0 100644 (file)
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -6,6 +6,7 @@
 #include <linux/kasan.h>
 #include <linux/kasan-tags.h>
 #include <linux/kfence.h>
+#include <linux/spinlock.h>
 #include <linux/stackdepot.h>
 
 #if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
@@ -249,6 +250,13 @@ struct kasan_global {
 struct kasan_alloc_meta {
        struct kasan_track alloc_track;
        /* Free track is stored in kasan_free_meta. */
+       /*
+        * aux_lock protects aux_stack from accesses from concurrent
+        * kasan_record_aux_stack calls. It is a raw spinlock to avoid sleeping
+        * on RT kernels, as kasan_record_aux_stack_noalloc can be called from
+        * non-sleepable contexts.
+        */
+       raw_spinlock_t aux_lock;
        depot_stack_handle_t aux_stack[2];
 };