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

[Mark Balançian <mbalant3@xxxxxxxxx>]

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@xxxxxxxxx> 
> > 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@xxxxxxxxx>
> > >
> > > ---
> >
> > 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@xxxxxxxxx
> > Profile: http://www.google.com/profiles/julian.calaby/