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Subject: Re: [PATCH] mailbox: fix a UAF bug in msg_submit()
To:     jassisinghbrar@gmail.com
Cc:     linux-kernel@vger.kernel.org, guoren@kernel.org
References: <20210806121521.124365-1-xianting.tian@linux.alibaba.com>
From:   Xianting TIan <xianting.tian@linux.alibaba.com>
Message-ID: <554d6b8d-0b09-f3cc-8124-b33131d1243f@linux.alibaba.com>
Date:   Tue, 10 Aug 2021 18:45:26 +0800
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Could I get the comments for the patch, thanks.


在 2021/8/6 下午8:15, Xianting Tian 写道:
> We met a UAF issue during our mailbox testing.
>
> In synchronous mailbox, we use mbox_send_message() to send a message
> and wait for completion. mbox_send_message() calls msg_submit() to
> send the message for the first time, if timeout, it will send the
> message in tx_tick() for the second time.
>
> We assume message sending failed for both two times,  then the message
> will be still in the internal buffer of a chan(chan->msg_data[idx]).
> It will be send again in the same way when mbox_send_message() is
> called next time. But, at this time this message (chan->msg_data[idx])
> may be a UAF pointer, as the message is passed to mailbox core by user.
> User may free it after last calling of mbox_send_message() returned
> or not. Who knows!!!
>
> In this patch, if the first time sending timeout, we pass timeout
> info(-ETIME) to msg_submit() when do the second time sending by
> tx_tick(). If it still send failed (chan->mbox->ops->send_data()
> returned non-zero value) in the second time, we will give up this
> message(chan->msg_count--) sending. It doesn't matter, user can chose
> to send it again.
>
> Actually, the issue I described above doesn't exist if
> 'chan->mbox->ops->send_data()' always return 0. Because if it always
> returns 0, we will always do 'chan->msg_count—' regardless of message
> sending success or failure. We have such mailbox driver, for example,
> hi6220_mbox_send_data() always return 0. But we still have mailbox
> drivers, which don't always return 0, for example, flexrm_send_data()
> of drivers/mailbox/bcm-flexrm-mailbox.c.
>
> Signed-off-by: Xianting Tian <xianting.tian@linux.alibaba.com>
> ---
>   drivers/mailbox/mailbox.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> index 3e7d4b20a..3e010aafa 100644
> --- a/drivers/mailbox/mailbox.c
> +++ b/drivers/mailbox/mailbox.c
> @@ -50,7 +50,7 @@ static int add_to_rbuf(struct mbox_chan *chan, void *mssg)
>   	return idx;
>   }
>   
> -static void msg_submit(struct mbox_chan *chan)
> +static void msg_submit(struct mbox_chan *chan, int last_submit)
>   {
>   	unsigned count, idx;
>   	unsigned long flags;
> @@ -75,7 +75,7 @@ static void msg_submit(struct mbox_chan *chan)
>   		chan->cl->tx_prepare(chan->cl, data);
>   	/* Try to submit a message to the MBOX controller */
>   	err = chan->mbox->ops->send_data(chan, data);
> -	if (!err) {
> +	if (!err || last_submit == -ETIME) {
>   		chan->active_req = data;
>   		chan->msg_count--;
>   	}
> @@ -101,7 +101,7 @@ static void tx_tick(struct mbox_chan *chan, int r)
>   	spin_unlock_irqrestore(&chan->lock, flags);
>   
>   	/* Submit next message */
> -	msg_submit(chan);
> +	msg_submit(chan, r);
>   
>   	if (!mssg)
>   		return;
> @@ -260,7 +260,7 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg)
>   		return t;
>   	}
>   
> -	msg_submit(chan);
> +	msg_submit(chan, 0);
>   
>   	if (chan->cl->tx_block) {
>   		unsigned long wait;