linux-kernel - Re: [PATCH] staging: lustre: fix sparse warning on LPROC_SEQ

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Message-ID: <20141205224143.GB5698@localhost.localdomain>
Date:	Fri, 5 Dec 2014 14:41:43 -0800
From:	Tristan Lelong <tristan@...ong.xyz>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	oleg.drokin@...el.com, andreas.dilger@...el.com, askb23@...il.com,
	john.hammond@...el.com, gdonald@...il.com, anhlq2110@...il.com,
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	rupran@...server.de, surya.seetharaman9@...il.com,
	Julia.Lawall@...6.fr, joe@...ches.com, a.terekhov@...il.com,
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	HPDD-discuss@...ts.01.org, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: lustre: fix sparse warning on LPROC_SEQ_FOPS
 macros

On Fri, Dec 05, 2014 at 01:27:23PM -0800, Greg KH wrote:
> On Fri, Dec 05, 2014 at 12:03:47AM -0800, Tristan Lelong wrote:
> >  static ssize_t
> > -fld_proc_hash_seq_write(struct file *file, const char *buffer,
> > -			size_t count, loff_t *off)
> > +fld_proc_hash_seq_write(struct file *file,
> > +				const char __user *buffer,
> > +				size_t count, loff_t *off)
> >  {
> >  	struct lu_client_fld *fld;
> >  	struct lu_fld_hash *hash = NULL;
> > +	char name[80];
> >  	int i;
> >  
> > +	if (count > 80)
> > +		return -ENAMETOOLONG;
> > +
> > +	if (copy_from_user(name, buffer, count) != 0)
> > +		return -EFAULT;
> 
> How was this code ever working before?

I have no idea, and was actually surprised that this was there.

> 
> And I know Joe asked, but how do you know that 80 is ok?  And why on the
> stack?

80 is the sizeof(struct lu_fld_hash.fh_name) and there is no define for that.
A few other structure members are using this 80 value internally, and as I told
Joe, I will analyze if they are all related and submit a patch to use a define instead.

> 
> Shouldn't you just compare count to strlen(fld_hash[i].fh_name)? like you
> do later on?
> 

This is actually done in the for loop already. I first compare with the maximum size,
then the loop use the strlen of each entries in the table, and finally does the strncmp.

> 
> Anyway, I don't like large stack variables like this, can you make it
> dynamic instead?
> 

I can definitely do this with a kmalloc, I'll submit a v2 tonight.

Thanks
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