Re: [PATCH 3/6] edac, mce_amd_inj: Modify flags attrigute to use string arguments

[Aravind Gopalakrishnan]

On 5/29/2015 8:49 AM, Borislav Petkov wrote:
> On Wed, May 27, 2015 at 02:03:35PM -0500, Aravind Gopalakrishnan wrote:
> >   
> > +#define MAX_FLAG_OPT_SIZE	10
> Why 10?
>
> This should be 2 and increased when another, longer injection type
> string gets introduced.

So I hit an issue when I have this as 2 and moving 'ret = cnt' statement 
(in flags_write() below) to after the check for MAX_FLAG_OPT_SIZE.

The problem was, if I did echo hw > flags;
I would get an error on dmesg like so-
[   78.692949] flags_write: Invalid flags value:

But the write would have actually gone through. i.e, if we do cat flags, 
the output was 'hw'.

The issue seems to be that 'cnt' of flags_write() is 3 (after accounting 
for a terminating NULL) when we enter the function (for this case),

Since we move 'ret = cnt;' statement to after the check, we end up 
returning 2.
And since it is less than 'cnt', we re-enter flags_write() for the final 
NULL character.
At this point, our comparisons with flags_options[] fail and we end up 
returning -EINVAL from __set_inj().
Hence the error on dmesg..

The fix to this was simply having MAX_FLAG_OPT_SIZE as 3. In this case, 
we already account for the NULL and flags_write()
returns the correct value upon success.
So I shall go ahead and make that change to MAX_FLAG_OPT_SIZE as 3 and 
increase it in subsequent patch for the apic interrupts.

Thanks,
-Aravind.


> >   
> > -DEFINE_SIMPLE_ATTRIBUTE(flags_fops, flags_get, flags_set, "%llu\n");
> > +static ssize_t flags_write(struct file *filp, const char __user *ubuf,
> > +			   size_t cnt, loff_t *ppos)
> > +{
> > +	char buf[MAX_FLAG_OPT_SIZE + 1];
> > +	int err;
> > +	size_t ret;
> > +
> > +	ret = cnt;
> You're assigning cnt to ret here...
>
> > +
> > +	if (cnt > MAX_FLAG_OPT_SIZE)
> > +		cnt = MAX_FLAG_OPT_SIZE;
> ... but correcting cnt afterwards. The assignment should be *after* that
> correction.
>
> > +
> > +	if (copy_from_user(&buf, ubuf, cnt))
> > +		return -EFAULT;
> > +
> > +	buf[cnt] = 0;
> > +
> > +	/* strip whitespaces.. */
> > +	strstrip(buf);
> > +
> > +	err = __set_inj(buf, cnt - 1);
> > +	if (err) {
> > +		pr_err("%s: Invalid flags value: %s\n", __func__, buf);
> > +		return err;
> > +	}
> > +
> > +	*ppos += ret;
> > +
> > +	return ret;
> > +}
> > +

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/