hostap: avoid uninitialized variable use in hfa384x_get_rid

The driver reads a value from hfa384x_from_bap(), which may fail,
and then assigns the value to a local variable. gcc detects that
in in the failure case, the 'rlen' variable now contains
uninitialized data:

In file included from ../drivers/net/wireless/intersil/hostap/hostap_pci.c:220:0:
drivers/net/wireless/intersil/hostap/hostap_hw.c: In function 'hfa384x_get_rid':
drivers/net/wireless/intersil/hostap/hostap_hw.c:842:5: warning: 'rec' may be used uninitialized in this function [-Wmaybe-uninitialized]
  if (le16_to_cpu(rec.len) == 0) {

To ensure we get consistent error handling here, this changes the code
to only set rlen if we actually read data correctly, which also takes
care of the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/net/wireless/intersil/hostap/hostap_hw.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

On Wed, Jan 27, 2016 at 02:45:26PM +0100, Arnd Bergmann wrote:
> To ensure we get consistent error handling here, this changes the code
> to only set rlen if we actually read data correctly, which also takes
> care of the warning.

It may be a good idea to do the job better.  Looking at the code:

        struct hfa384x_rid_hdr rec;

        spin_lock_bh(&local->baplock);

        res = hfa384x_setup_bap(dev, BAP0, rid, 0);
        if (!res)
                res = hfa384x_from_bap(dev, BAP0, &rec, sizeof(rec));

The only thing which initialises any of "rec" is that function call.
The following lines are:

        if (le16_to_cpu(rec.len) == 0) {
                /* RID not available */
                res = -ENODATA;
        }

        rlen = (le16_to_cpu(rec.len) - 1) * 2;

So, why give the compiler a hard time as you're doing, why make the code
harder to read.  What's wrong with:

	spin_lock_bh(&local->baplock);

	res = hfa384x_setup_bap(dev, BAP0, rid, 0);
	if (res)
		goto unlock;

	res = hfa384x_from_bap(dev, BAP0, &rec, sizeof(rec));
	if (res)
		goto unlock;

	if (le16_to_cpu(rec.len) == 0) {
		/* RID not available */
		res = -ENODATA;
		goto unlock;
	}

	rlen = (le16_to_cpu(rec.len) - 1) * 2;
	if (exact_len && rlen != len) {
		printk(KERN_DEBUG "%s: hfa384x_get_rid - RID len mismatch: rid=0x%04x, len=%d (expected %d)\n",
		       dev->name, rid, rlen, len);
		res = -ENODATA;
		goto unlock;
	}

	res = hfa384x_from_bap(dev, BAP0, buf, len);
unlock:
	spin_unlock_bh(&local->baplock);

?

On Wednesday 27 January 2016 19:26:13 Russell King - ARM Linux wrote:
> On Wed, Jan 27, 2016 at 02:45:26PM +0100, Arnd Bergmann wrote:
> So, why give the compiler a hard time as you're doing, why make the code
> harder to read.  What's wrong with:
> 
>         spin_lock_bh(&local->baplock);
> 
>         res = hfa384x_setup_bap(dev, BAP0, rid, 0);
>         if (res)
>                 goto unlock;
> 
>         res = hfa384x_from_bap(dev, BAP0, &rec, sizeof(rec));
>         if (res)
>                 goto unlock;
> 
>         if (le16_to_cpu(rec.len) == 0) {
>                 /* RID not available */
>                 res = -ENODATA;
>                 goto unlock;
>         }
> 
>         rlen = (le16_to_cpu(rec.len) - 1) * 2;
>         if (exact_len && rlen != len) {
>                 printk(KERN_DEBUG "%s: hfa384x_get_rid - RID len mismatch: rid=0x%04x, len=%d (expected %d)\n",
>                        dev->name, rid, rlen, len);
>                 res = -ENODATA;
>                 goto unlock;
>         }
> 
>         res = hfa384x_from_bap(dev, BAP0, buf, len);
> unlock:
>         spin_unlock_bh(&local->baplock);
> 
> ?
> 

Good idea, I'll send a new version.

	Arnd