linux-kernel - [PATCH] binder: fix yet another UAF in binder

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Message-ID: <20250524220758.915028-1-cmllamas@google.com>
Date: Sat, 24 May 2025 22:07:58 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Alice Ryhl <aliceryhl@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Arve Hjønnevåg" <arve@...roid.com>, Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>, 
	Joel Fernandes <joel@...lfernandes.org>, Christian Brauner <brauner@...nel.org>, 
	Carlos Llamas <cmllamas@...gle.com>, Suren Baghdasaryan <surenb@...gle.com>, Li Li <dualli@...gle.com>
Cc: kernel-team@...roid.com, stable@...r.kernel.org, 
	syzbot+4af454407ec393de51d6@...kaller.appspotmail.com, 
	"open list:ANDROID DRIVERS" <linux-kernel@...r.kernel.org>
Subject: [PATCH] binder: fix yet another UAF in binder_devices

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@...r.kernel.org
Fixes: 12d909cac1e1 ("binderfs: add new binder devices to binder_devices")
Reported-by: syzbot+4af454407ec393de51d6@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4af454407ec393de51d6
Tested-by: syzbot+4af454407ec393de51d6@...kaller.appspotmail.com
Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
---
 drivers/android/binder.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 682bbe4ad550..c463ca4a8fff 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -5241,6 +5241,7 @@ static void binder_free_proc(struct binder_proc *proc)
 			__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);
 	}
-- 
2.49.0.1151.ga128411c76-goog