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Subject: Re: [PATCH] mwifiex: Fix divide error in mwifiex_usb_dnld_fw
To:     Wan Jiabing <wanjiabing@vivo.com>,
        Amitkumar Karwar <amitkarwar@gmail.com>,
        Ganapathi Bhat <ganapathi017@gmail.com>,
        Sharvari Harisangam <sharvari.harisangam@nxp.com>,
        Xinming Hu <huxinming820@gmail.com>,
        Kalle Valo <kvalo@codeaurora.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     kael_w@yeah.net,
        syzbot+4e7b6c94d22f4bfca9a0@syzkaller.appspotmail.com
References: <20211019033101.27658-1-wanjiabing@vivo.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <1ae64510-0519-4852-a2a0-5c32490a195c@gmail.com>
Date:   Mon, 18 Oct 2021 21:04:27 -0700
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On 10/18/21 8:31 PM, Wan Jiabing wrote:
> This patch try to fix bug reported by syzkaller:
> divide error: 0000 [#1] SMP KASAN
> CPU: 1 PID: 17 Comm: kworker/1:0 Not tainted 5.15.0-rc5-syzkaller #0
> Hardware name: Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: events request_firmware_work_func
> RIP: 0010:mwifiex_write_data_sync drivers/net/wireless/marvell/mwifiex/usb.c:696 [inline]
> RIP: 0010:mwifiex_prog_fw_w_helper drivers/net/wireless/marvell/mwifiex/usb.c:1437 [inline]
> RIP: 0010:mwifiex_usb_dnld_fw+0xabd/0x11a0 drivers/net/wireless/marvell/mwifiex/usb.c:1518
> Call Trace:
>  _mwifiex_fw_dpc+0x181/0x10a0 drivers/net/wireless/marvell/mwifiex/main.c:542
>  request_firmware_work_func+0x12c/0x230 drivers/base/firmware_loader/main.c:1081
>  process_one_work+0x9bf/0x1620 kernel/workqueue.c:2297
>  worker_thread+0x658/0x11f0 kernel/workqueue.c:2444
>  kthread+0x3c2/0x4a0 kernel/kthread.c:319
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> 
> Link: https://syzkaller.appspot.com/bug?extid=4e7b6c94d22f4bfca9a0

Please provide a Fixes: tag

> Reported-and-tested-by: syzbot+4e7b6c94d22f4bfca9a0@syzkaller.appspotmail.com
> Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
> ---
>  drivers/net/wireless/marvell/mwifiex/usb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/marvell/mwifiex/usb.c b/drivers/net/wireless/marvell/mwifiex/usb.c
> index 426e39d4ccf0..c24ec27d4057 100644
> --- a/drivers/net/wireless/marvell/mwifiex/usb.c
> +++ b/drivers/net/wireless/marvell/mwifiex/usb.c
> @@ -693,7 +693,7 @@ static int mwifiex_write_data_sync(struct mwifiex_adapter *adapter, u8 *pbuf,
>  	struct usb_card_rec *card = adapter->card;
>  	int actual_length, ret;
>  
> -	if (!(*len % card->bulk_out_maxpktsize))
> +	if (card->bulk_out_maxpktsize && !(*len % card->bulk_out_maxpktsize))


Are you sure this fix is not working around the real bug ?

In which cases bulk_out_maxpktsize would be zero ?

If this is a valid case, this needs to be explained in the changelog.

>  		(*len)++;
>  
>  	/* Send the data block */
>