[PATCH 2/4] carl9170: fix debugfs crashes

[Christian Lamparter <chunkeey@googlemail.com>]

On Wednesday, September 21, 2016 12:13:25 PM CEST Greg KH wrote:
> On Sat, Sep 17, 2016 at 09:43:02PM +0200, Christian Lamparter wrote:
> > Ben Greear reported:
> > > I see lots of instability as soon as I load up the carl9710 NIC.
> > > My application is going to be poking at it's debugfs files...
> > >
> > > BUG: KASAN: slab-out-of-bounds in carl9170_debugfs_read+0xd5/0x2a0
> > > [carl9170] at addr ffff8801bc1208b0
> > > Read of size 8 by task btserver/5888
> > > =======================================================================
> > > BUG kmalloc-256 (Tainted: G        W      ): kasan: bad access detected
> > > -----------------------------------------------------------------------
> > >
> > > INFO: Allocated in seq_open+0x50/0x100 age=2690 cpu=2 pid=772
> > >...
> > 
> > This breakage was caused by the introduction of intermediate
> > fops in debugfs by commit 9fd4dcece43a
> > ("debugfs: prevent access to possibly dead file_operations at file open")
> > 
> > Thankfully, the original/real fops are still available in d_fsdata.
> > 
> > Reported-by: Ben Greear <greearb@candelatech.com>
> > Reviewed-by: Nicolai Stange <nicstange@gmail.com>
> > Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
> > Acked-by: Kalle Valo <kvalo@codeaurora.org>
> > Cc: stable <stable@vger.kernel.org> # 4.7+
> > ---
> >  drivers/net/wireless/ath/carl9170/debug.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/wireless/ath/carl9170/debug.c b/drivers/net/wireless/ath/carl9170/debug.c
> > index 01a0919..ad7ffd5 100644
> > --- a/drivers/net/wireless/ath/carl9170/debug.c
> > +++ b/drivers/net/wireless/ath/carl9170/debug.c
> > @@ -75,7 +75,7 @@ static ssize_t carl9170_debugfs_read(struct file *file, char __user *userbuf,
> >  
> >  	if (!ar)
> >  		return -ENODEV;
> > -	dfops = container_of(file->f_path.dentry->d_fsdata,
> > +	dfops = container_of(debugfs_real_fops(file),
> >  			     struct carl9170_debugfs_fops, fops);
> >  
> >  	if (!dfops->read)
> > @@ -128,7 +128,7 @@ static ssize_t carl9170_debugfs_write(struct file *file,
> >  
> >  	if (!ar)
> >  		return -ENODEV;
> > -	dfops = container_of(file->f_path.dentry->d_fsdata,
> > +	dfops = container_of(debugfs_real_fops(file),
> >  			     struct carl9170_debugfs_fops, fops);
> >  	if (!dfops->write)
> >  		return -ENOSYS;
> 
> What tree is this against?  I can't apply it to 4.8-rc5, or 4.8-rc7, are
> you sure it is still needed?
---
Yes, the patch is needed. That said I screwed this patch up and as a result
it is faulty. I'll send out v2 shortly

Thanks,
Christian