linux-kernel - Re: [PATCH] binder: fix double-free in dbitmap

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Message-ID: <CAH5fLghdcCx_OrCY-xq2gxug4j4RTMnmZsoB-Y18tLRp=Z5R-g@mail.gmail.com>
Date: Tue, 16 Sep 2025 17:22:50 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Carlos Llamas <cmllamas@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arve Hjønnevåg <arve@...roid.com>, 
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>, 
	Joel Fernandes <joelagnelf@...dia.com>, Christian Brauner <brauner@...nel.org>, 
	Suren Baghdasaryan <surenb@...gle.com>, kernel-team@...roid.com, linux-kernel@...r.kernel.org, 
	Tiffany Yang <ynaffit@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH] binder: fix double-free in dbitmap

On Tue, Sep 16, 2025 at 12:12 AM Carlos Llamas <cmllamas@...gle.com> wrote:
>
> A process might fail to allocate a new bitmap when trying to expand its
> proc->dmap. In that case, dbitmap_grow() fails and frees the old bitmap
> via dbitmap_free(). However, the driver calls dbitmap_free() again when
> the same process terminates, leading to a double-free error:
>
>   ==================================================================
>   BUG: KASAN: double-free in binder_proc_dec_tmpref+0x2e0/0x55c
>   Free of addr ffff00000b7c1420 by task kworker/9:1/209
>
>   CPU: 9 UID: 0 PID: 209 Comm: kworker/9:1 Not tainted 6.17.0-rc6-dirty #5 PREEMPT
>   Hardware name: linux,dummy-virt (DT)
>   Workqueue: events binder_deferred_func
>   Call trace:
>    kfree+0x164/0x31c
>    binder_proc_dec_tmpref+0x2e0/0x55c
>    binder_deferred_func+0xc24/0x1120
>    process_one_work+0x520/0xba4
>   [...]
>
>   Allocated by task 448:
>    __kmalloc_noprof+0x178/0x3c0
>    bitmap_zalloc+0x24/0x30
>    binder_open+0x14c/0xc10
>   [...]
>
>   Freed by task 449:
>    kfree+0x184/0x31c
>    binder_inc_ref_for_node+0xb44/0xe44
>    binder_transaction+0x29b4/0x7fbc
>    binder_thread_write+0x1708/0x442c
>    binder_ioctl+0x1b50/0x2900
>   [...]
>   ==================================================================
>
> Fix this issue by marking proc->map NULL in dbitmap_free().
>
> Cc: stable@...r.kernel.org
> Fixes: 15d9da3f818c ("binder: use bitmap for faster descriptor lookup")
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>

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