Re: [syzbot] [kernel?] KASAN: slab-use-after-free Write in binder_add_device

[Carlos Llamas <cmllamas@google.com>]

On Sun, Mar 16, 2025 at 03:51:27PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    b7f94fcf5546 Merge tag 'sched_ext-for-6.14-rc6-fixes' of g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=134f303f980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cdc24cb631dc9bc4
> dashboard link: https://syzkaller.appspot.com/bug?extid=810b8555076779a07399
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

#syz test

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 76052006bd87..bf79a0e339fe 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -79,6 +79,8 @@ static HLIST_HEAD(binder_deferred_list);
 static DEFINE_MUTEX(binder_deferred_lock);
 
 static HLIST_HEAD(binder_devices);
+static DEFINE_SPINLOCK(binder_devices_lock);
+
 static HLIST_HEAD(binder_procs);
 static DEFINE_MUTEX(binder_procs_lock);
 
@@ -6929,7 +6931,16 @@ const struct binder_debugfs_entry binder_debugfs_entries[] = {
 
 void binder_add_device(struct binder_device *device)
 {
+	spin_lock(&binder_devices_lock);
 	hlist_add_head(&device->hlist, &binder_devices);
+	spin_unlock(&binder_devices_lock);
+}
+
+void binder_remove_device(struct binder_device *device)
+{
+	spin_lock(&binder_devices_lock);
+	hlist_del_init(&device->hlist);
+	spin_unlock(&binder_devices_lock);
 }
 
 static int __init init_binder_device(const char *name)
@@ -6956,7 +6967,7 @@ static int __init init_binder_device(const char *name)
 		return ret;
 	}
 
-	hlist_add_head(&binder_device->hlist, &binder_devices);
+	binder_add_device(binder_device);
 
 	return ret;
 }
@@ -7018,7 +7029,7 @@ static int __init binder_init(void)
 err_init_binder_device_failed:
 	hlist_for_each_entry_safe(device, tmp, &binder_devices, hlist) {
 		misc_deregister(&device->miscdev);
-		hlist_del(&device->hlist);
+		binder_remove_device(device);
 		kfree(device);
 	}
 
diff --git a/drivers/android/binder_internal.h b/drivers/android/binder_internal.h
index e4eb8357989c..c5d68c1d3780 100644
--- a/drivers/android/binder_internal.h
+++ b/drivers/android/binder_internal.h
@@ -584,9 +584,13 @@ struct binder_object {
 /**
  * Add a binder device to binder_devices
  * @device: the new binder device to add to the global list
- *
- * Not reentrant as the list is not protected by any locks
  */
 void binder_add_device(struct binder_device *device);
 
+/**
+ * Remove a binder device to binder_devices
+ * @device: the binder device to remove from the global list
+ */
+void binder_remove_device(struct binder_device *device);
+
 #endif /* _LINUX_BINDER_INTERNAL_H */
diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index 94c6446604fc..44d430c4ebef 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -274,7 +274,7 @@ static void binderfs_evict_inode(struct inode *inode)
 	mutex_unlock(&binderfs_minors_mutex);
 
 	if (refcount_dec_and_test(&device->ref)) {
-		hlist_del_init(&device->hlist);
+		binder_remove_device(device);
 		kfree(device->context.name);
 		kfree(device);
 	}