Re: [PATCH v3] lsilogic mpt fusion: mptctl: Fixed race condition around mptctl_id variable using mutexes

["Mark Balançian" <mbalant3@gmail.com>]

Hello Mister Prakash, Calaby, and Subramani,

I also please request your reply to my previous message before the end 
of this Thursday the latest, as I am partaking in an evaluation period 
from the organization I am working for with a deadline very close to 
that time.

Thank you,

Mark

On 2019-08-20 7:46 a.m., Mark Balantzyan wrote:
> Hi all,
>
> The race condition in the mptctl driver I'm wishing to have confirmed 
> is evidenced by the pair of call chains:
>
> compat_mpctl_ioctl -> compat_mpt_command -> mptctl_do_mpt_command 
> which calls mpt_get_msg_frame(mptctl_id, ioc)
>
> and
>
> __mptctl_ioctl -> mpt_fw_download -> mptctl_do_fw_download which calls 
> mpt_put_msg_frame(mptctl_id, iocp, mf) and calls 
> mpt_get_msg_frame(mptctl_id, iocp)
>
> Since ioctl can be called at any time, accessing of mptctl_id occurs 
> concurrently between threads causing a race.
>
> I realize in past messages I've tried to patch by surrounding all 
> instances of mptctl_id with mutexes but I'm focusing this time on one 
> clear instance of the race condition involving the variable mptctl_id, 
> since Julian asks what the exact race condition is with respect to the 
> case.
>
> Please let me know the confirmation or not confirmation of this race 
> possibility.
>
> Thank you,
> Mark
>
> On Sun, 18 Aug 2019, Julian Calaby wrote:
>
>> Hi Mark,
>>
>> On Thu, Aug 15, 2019 at 8:02 PM Mark Balantzyan <mbalant3@gmail.com> 
>> wrote:
>>>
>>> Certain functions in the driver, such as mptctl_do_fw_download() and
>>> mptctl_do_mpt_command(), rely on the instance of mptctl_id, which 
>>> does the
>>> id-ing. There is race condition possible when these functions 
>>> operate in
>>> concurrency. Via, mutexes, the functions are mutually signalled to 
>>> cooperate.
>>>
>>> Changelog v2
>>>
>>> Lacked a version number but added properly terminated else condition at
>>> (former) line 2300.
>>>
>>> Changelog v3
>>>
>>> Fixes "return -EAGAIN" lines which were erroneously tabbed as if to 
>>> be guarded
>>> by "if" conditions lying above them.
>>>
>>> Signed-off-by: Mark Balantzyan <mbalant3@gmail.com>
>>>
>>> ---
>>
>> Changelog should be down here after the "---"
>>
>>>  drivers/message/fusion/mptctl.c | 43 +++++++++++++++++++++++++--------
>>>  1 file changed, 33 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/message/fusion/mptctl.c 
>>> b/drivers/message/fusion/mptctl.c
>>> index 4470630d..3270843c 100644
>>> --- a/drivers/message/fusion/mptctl.c
>>> +++ b/drivers/message/fusion/mptctl.c
>>> @@ -816,12 +816,15 @@ mptctl_do_fw_download(int ioc, char __user 
>>> *ufwbuf, size_t fwlen)
>>>
>>>                 /*  Valid device. Get a message frame and construct 
>>> the FW download message.
>>>                 */
>>> +               mutex_lock(&mpctl_mutex);
>>>                 if ((mf = mpt_get_msg_frame(mptctl_id, iocp)) == NULL)
>>> -                       return -EAGAIN;
>>> +                       mutex_unlock(&mpctl_mutex);
>>> +               return -EAGAIN;
>>
>> Are you sure this is right?
>>
>> 1. We're now exiting early with -EAGAIN regardless of the result of
>> mpt_get_msg_frame()
>> 2. If the result of mpt_get_msg_frame() is not NULL, we don't unlock 
>> the mutex
>>
>> Do you mean something like:
>>
>> - - - - - -
>>
>> mutex_lock(&mpctl_mutex);
>> mf = mpt_get_msg_frame(mptctl_id, iocp);
>> mutex_unlock(&mpctl_mutex);
>>
>> if (mf == NULL) {
>>
>> - - - - - -
>>
>>> @@ -1889,8 +1894,10 @@ mptctl_do_mpt_command (struct 
>>> mpt_ioctl_command karg, void __user *mfPtr)
>>>
>>>         /* Get a free request frame and save the message context.
>>>          */
>>> +       mutex_lock(&mpctl_mutex);
>>>          if ((mf = mpt_get_msg_frame(mptctl_id, ioc)) == NULL)
>>> -                return -EAGAIN;
>>> +               mutex_unlock(&mpctl_mutex);
>>> +        return -EAGAIN;
>>
>> Same comments here.
>>
>>> @@ -2563,7 +2576,9 @@ mptctl_hp_hostinfo(unsigned long arg, unsigned 
>>> int data_size)
>>>         /*
>>>          * Gather ISTWI(Industry Standard Two Wire Interface) Data
>>>          */
>>> +       mutex_lock(&mpctl_mutex);
>>>         if ((mf = mpt_get_msg_frame(mptctl_id, ioc)) == NULL) {
>>> +       mutex_unlock(&mpctl_mutex);
>>
>> This line needs to be indented to match the line below, also we don't
>> unlock the mutex if mpt_get_msg_frame() is not NULL.
>>
>>> @@ -3010,9 +3027,11 @@ static int __init mptctl_init(void)
>>>          *  Install our handler
>>>          */
>>>         ++where;
>>> +       mutex_lock(&mpctl_mutex);
>>>         mptctl_id = mpt_register(mptctl_reply, MPTCTL_DRIVER,
>>>             "mptctl_reply");
>>>         if (!mptctl_id || mptctl_id >= MPT_MAX_PROTOCOL_DRIVERS) {
>>> +               mutex_unlock(&mpctl_mutex);
>>
>> Why not use a local variable and only update the global variable if 
>> it's valid?
>>
>>>                 printk(KERN_ERR MYNAM ": ERROR: Failed to register 
>>> with Fusion MPT base driver\n");
>>>                 misc_deregister(&mptctl_miscdev);
>>>                 err = -EBUSY;
>>> @@ -3022,13 +3041,14 @@ static int __init mptctl_init(void)
>>>         mptctl_taskmgmt_id = mpt_register(mptctl_taskmgmt_reply, 
>>> MPTCTL_DRIVER,
>>>             "mptctl_taskmgmt_reply");
>>>         if (!mptctl_taskmgmt_id || mptctl_taskmgmt_id >= 
>>> MPT_MAX_PROTOCOL_DRIVERS) {
>>> +               mutex_unlock(&mpctl_mutex);
>>
>> Same comment here.
>>
>>> @@ -3044,13 +3064,14 @@ out_fail:
>>>  /*=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=*/ 
>>>
>>>  static void mptctl_exit(void)
>>>  {
>>> +       mutex_lock(&mpctl_mutex);
>>>         misc_deregister(&mptctl_miscdev);
>>>         printk(KERN_INFO MYNAM ": Deregistered /dev/%s @ 
>>> (major,minor=%d,%d)\n",
>>>                          mptctl_miscdev.name, MISC_MAJOR, 
>>> mptctl_miscdev.minor);
>>>
>>>         /* De-register event handler from base module */
>>>         mpt_event_deregister(mptctl_id);
>>> -
>>> +
>>
>> Please don't add trailing whitespace.
>>
>> Did you test this on real hardware? I'd expect it to deadlock and
>> crash almost immediately.
>>
>> Also, it might be worthwhile creating accessor functions for the
>> mptctl variables or using atomics, that way the locking doesn't need
>> to be right every time they're used.
>>
>> Finally, what's the exact race condition here? Are the functions you
>> reference changing the values of the mptctl variables while other code
>> is using them? These functions appear to be setup functions, so why
>> are those variables being used before the device is fully set up?
>> Single usages of those variables shouldn't be subject to race
>> conditions, so you shouldn't need mutexes around those.
>>
>> Thanks,
>>
>> -- 
>> Julian Calaby
>>
>> Email: julian.calaby@gmail.com
>> Profile: http://www.google.com/profiles/julian.calaby/
>>