[PATCH] binderfs: fix use-after-free in binder_devices

From: Carlos Llamas
Date: Thu Jan 30 2025 - 16:58:37 EST


Devices created through binderfs are added to the global binder_devices
list but are not removed before being destroyed. This leads to dangling
pointers in the list and subsequent use-after-free errors:

==================================================================
BUG: KASAN: slab-use-after-free in binder_add_device+0x5c/0x9c
Write of size 8 at addr ffff0000c258d708 by task mount/653

CPU: 7 UID: 0 PID: 653 Comm: mount Not tainted 6.13.0-09030-g6d61a53dd6f5 #1
Hardware name: linux,dummy-virt (DT)
Call trace:
binder_add_device+0x5c/0x9c
binderfs_binder_device_create+0x690/0x84c
[...]
__arm64_sys_mount+0x324/0x3bc

Allocated by task 632:
binderfs_binder_device_create+0x168/0x84c
binder_ctl_ioctl+0xfc/0x184
[...]
__arm64_sys_ioctl+0x110/0x150

Freed by task 649:
kfree+0xe0/0x338
binderfs_evict_inode+0x138/0x1dc
[...]
==================================================================

Remove devices from binder_devices before destroying them.

Cc: Li Li <dualli@xxxxxxxxxx>
Reported-by: syzbot+7015dcf45953112c8b45@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=7015dcf45953112c8b45
Fixes: 12d909cac1e1 ("binderfs: add new binder devices to binder_devices")
Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
---
drivers/android/binderfs.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index bc6bae76ccaf..94c6446604fc 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -274,6 +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);
kfree(device->context.name);
kfree(device);
}
--
2.48.1.362.g079036d154-goog