Re: [PATCH] binder: fix yet another UAF in binder_devices

[Alice Ryhl <aliceryhl@google.com>]

On Sat, May 24, 2025 at 10:07:58PM +0000, Carlos Llamas wrote:
> 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>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>