[PATCH 6.15 28/34] binder: fix yet another UAF in binder_devices

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Carlos Llamas <cmllamas@google.com>

commit 9857af0fcff385c75433f2162c30c62eb912ef6d upstream.

Commit e77aff5528a18 ("binderfs: fix use-after-free in binder_devices")
addressed a use-after-free where devices could be released without first
being removed from the binder_devices list. However, there is a similar
path in binder_free_proc() that was missed:

  ==================================================================
  BUG: KASAN: slab-use-after-free in binder_remove_device+0xd4/0x100
  Write of size 8 at addr ffff0000c773b900 by task umount/467
  CPU: 12 UID: 0 PID: 467 Comm: umount Not tainted 6.15.0-rc7-00138-g57483a362741 #9 PREEMPT
  Hardware name: linux,dummy-virt (DT)
  Call trace:
   binder_remove_device+0xd4/0x100
   binderfs_evict_inode+0x230/0x2f0
   evict+0x25c/0x5dc
   iput+0x304/0x480
   dentry_unlink_inode+0x208/0x46c
   __dentry_kill+0x154/0x530
   [...]

  Allocated by task 463:
   __kmalloc_cache_noprof+0x13c/0x324
   binderfs_binder_device_create.isra.0+0x138/0xa60
   binder_ctl_ioctl+0x1ac/0x230
  [...]

  Freed by task 215:
   kfree+0x184/0x31c
   binder_proc_dec_tmpref+0x33c/0x4ac
   binder_deferred_func+0xc10/0x1108
   process_one_work+0x520/0xba4
  [...]
  ==================================================================

Call binder_remove_device() within binder_free_proc() to ensure the
device is removed from the binder_devices list before being kfreed.

Cc: stable@vger.kernel.org
Fixes: 12d909cac1e1 ("binderfs: add new binder devices to binder_devices")
Reported-by: syzbot+4af454407ec393de51d6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4af454407ec393de51d6
Tested-by: syzbot+4af454407ec393de51d6@syzkaller.appspotmail.com
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20250524220758.915028-1-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/android/binder.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -5246,6 +5246,7 @@ static void binder_free_proc(struct bind
 			__func__, proc->outstanding_txns);
 	device = container_of(proc->context, struct binder_device, context);
 	if (refcount_dec_and_test(&device->ref)) {
+		binder_remove_device(device);
 		kfree(proc->context->name);
 		kfree(device);
 	}