linux-kernel - Re: [PATCH] misc: fastrpc: Fix a Use after-free-bug by race condition

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Message-ID: <1853ef42-7d04-be93-a728-5092a734275f@linaro.org>
Date:   Wed, 22 Mar 2023 08:40:02 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     sangsup lee <k1rh4.lee@...il.com>
Cc:     Amol Maheshwari <amahesh@....qualcomm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] misc: fastrpc: Fix a Use after-free-bug by race condition



On 22/03/2023 01:59, sangsup lee wrote:
> Sounds great.
> 
> Thank you for your recommendation.
> The patch code that you recommend is clear and simple.
> Please patch this.
> 
> Signed-off-by: Sangsup lee <k1rh4.lee@...il.com>
> ---

Please follow kernel patch submission guidelines, any changes to code 
should be send as new version of patch.

Have a look at Documentation/process/submitting-patches.rst for more 
information.

thanks,
Srini
>   drivers/misc/fastrpc.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 93ebd174d848..aa1cf0e9f4ed 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -1901,7 +1901,9 @@ static long fastrpc_device_ioctl(struct file
> *file, unsigned int cmd,
>                  err = fastrpc_req_mmap(fl, argp);
>                  break;
>          case FASTRPC_IOCTL_MUNMAP:
> +               mutex_lock(&fl->mutex);
>                  err = fastrpc_req_munmap(fl, argp);
> +               mutex_unlock(&fl->mutex);
>                  break;
>          case FASTRPC_IOCTL_MEM_MAP:
>                  err = fastrpc_req_mem_map(fl, argp);
> --
> 2.25.1
> 
> 
> 2023년 3월 21일 (화) 오후 6:27, Srinivas Kandagatla
> <srinivas.kandagatla@...aro.org>님이 작성:
>>
>> Thanks Sangsup for reporting the issue and sharing the patch,
>>
>> Sorry, for some reason I missed this patch.
>>
>> On 16/02/2023 01:41, Sangsup Lee wrote:
>>> This patch adds mutex_lock for fixing an Use-after-free bug.
>>> fastrpc_req_munmap_impl can be called concurrently in multi-threded environments.
>>> The buf which is allocated by list_for_each_safe can be used after another thread frees it.
>>>
>> Commit log can be improved here to something like:
>>
>> fastrcp_munmap takes two steps to unmap the memory, first to find a
>> matching fastrpc buf in the list and second is to send request to DSP to
>> unmap it.
>> There is a potentially window of race between these two operations,
>> which can lead to user-after-free.
>>
>> Fix this by adding locking around this two operations.
>>
>>> Signed-off-by: Sangsup Lee <k1rh4.lee@...il.com>
>>> ---
>>>    drivers/misc/fastrpc.c | 7 ++++++-
>>>    1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
>>> index 5310606113fe..c4b5fa4a50a6 100644
>>> --- a/drivers/misc/fastrpc.c
>>> +++ b/drivers/misc/fastrpc.c
>>> @@ -1806,10 +1806,12 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
>>>        struct fastrpc_buf *buf = NULL, *iter, *b;
>>>        struct fastrpc_req_munmap req;
>>>        struct device *dev = fl->sctx->dev;
>>> +     int err;
>>>
>>>        if (copy_from_user(&req, argp, sizeof(req)))
>>>                return -EFAULT;
>>>
>>> +     mutex_lock(&fl->mutex);
>>>        spin_lock(&fl->lock);
>>>        list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
>>>                if ((iter->raddr == req.vaddrout) && (iter->size == req.size)) {
>>> @@ -1822,10 +1824,13 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
>>>        if (!buf) {
>>>                dev_err(dev, "mmap\t\tpt 0x%09llx [len 0x%08llx] not in list\n",
>>>                        req.vaddrout, req.size);
>>> +             mutex_unlock(&fl->mutex);
>>>                return -EINVAL;
>>>        }
>>>
>>> -     return fastrpc_req_munmap_impl(fl, buf);
>>> +     err = fastrpc_req_munmap_impl(fl, buf);
>>> +     mutex_unlock(&fl->mutex);
>>> +     return err;
>>
>> How about moving the locking to ioctl:
>>
>> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
>> index a701132638cf..2f217071a6c3 100644
>> --- a/drivers/misc/fastrpc.c
>> +++ b/drivers/misc/fastrpc.c
>> @@ -2087,7 +2087,9 @@ static long fastrpc_device_ioctl(struct file
>> *file, unsigned int cmd,
>>                   err = fastrpc_req_mmap(fl, argp);
>>                   break;
>>           case FASTRPC_IOCTL_MUNMAP:
>> +               mutex_lock(&fl->mutex);
>>                   err = fastrpc_req_munmap(fl, argp);
>> +               mutex_unlock(&fl->mutex);
>>                   break;
>>           case FASTRPC_IOCTL_MEM_MAP:
>>                   err = fastrpc_req_mem_map(fl, argp);
>>
>>
>> thanks,
>> srini
>>>    }
>>>
>>>    static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)