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Thu, 07 May 2020 03:11:22 -0700 (PDT) Subject: Re: [PATCH] media: usb: ttusb-dec: avoid buffer overflow in ttusb_dec_handle_irq() when DMA failures/attacks occur To: Sean Young Cc: mchehab@kernel.org, kstewart@linuxfoundation.org, tomasbortoli@gmail.com, gregkh@linuxfoundation.org, allison@lohutok.net, tglx@linutronix.de, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200505142110.7620-1-baijiaju1990@gmail.com> <20200507084332.GA14459@gofer.mess.org> From: Jia-Ju Bai Message-ID: <4f95bc0d-0b75-dd75-642c-b2238feb9890@gmail.com> Date: Thu, 7 May 2020 18:11:06 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200507084332.GA14459@gofer.mess.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Thanks for the reply, Sean :) On 2020/5/7 16:43, Sean Young wrote: > On Tue, May 05, 2020 at 10:21:10PM +0800, Jia-Ju Bai wrote: >> Signed-off-by: Jia-Ju Bai >> --- >> drivers/media/usb/ttusb-dec/ttusb_dec.c | 9 +++++---- >> 1 file changed, 5 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/media/usb/ttusb-dec/ttusb_dec.c b/drivers/media/usb/ttusb-dec/ttusb_dec.c >> index 3198f9624b7c..8543c552515b 100644 >> --- a/drivers/media/usb/ttusb-dec/ttusb_dec.c >> +++ b/drivers/media/usb/ttusb-dec/ttusb_dec.c >> @@ -250,6 +250,7 @@ static void ttusb_dec_handle_irq( struct urb *urb) >> struct ttusb_dec *dec = urb->context; >> char *buffer = dec->irq_buffer; >> int retval; >> + u8 index = buffer[4]; >> >> switch(urb->status) { >> case 0: /*success*/ >> @@ -281,11 +282,11 @@ static void ttusb_dec_handle_irq( struct urb *urb) >> * this should/could be added later ... >> * for now lets report each signal as a key down and up >> */ >> - if (buffer[4] - 1 < ARRAY_SIZE(rc_keys)) { > Here buffer[4] is signed char, so if buffer[4] == 0 then (buffer[4] - 1) = -1, > this becomes "if (-1 < ARRAY_SIZE(rc_keys))", which evaluates to false, > due to it becoming an unsigned compare. _I think_. I think you are right. Maybe I should use "int index = buffer[4]" here. >> - dprintk("%s:rc signal:%d\n", __func__, buffer[4]); >> - input_report_key(dec->rc_input_dev, rc_keys[buffer[4] - 1], 1); >> + if (index - 1 < ARRAY_SIZE(rc_keys)) { >> + dprintk("%s:rc signal:%d\n", __func__, index); >> + input_report_key(dec->rc_input_dev, rc_keys[index - 1], 1); >> input_sync(dec->rc_input_dev); >> - input_report_key(dec->rc_input_dev, rc_keys[buffer[4] - 1], 0); >> + input_report_key(dec->rc_input_dev, rc_keys[index - 1], 0); > Like Greg said, this patch reduces the number of dereferences and makes > the code much cleaner, but the commit message is misleading. Okay, I will change my log and send a new patch. Best wishes, Jia-Ju Bai