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[PATCH] hostap: avoid uninitialized variable use in hfa384x_get_rid

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  [PATCH] hostap: avoid uninitialized variable use in hfa384x_get_rid Arnd Bergmann <arnd@arndb.de> - 2016-01-27 14:50 +0100
    Re: [PATCH] hostap: avoid uninitialized variable use in  hfa384x_get_rid Russell King - ARM Linux <linux@arm.linux.org.uk> - 2016-01-27 20:30 +0100

#1318964 — [PATCH] 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(-)

diff --git a/drivers/net/wireless/intersil/hostap/hostap_hw.c b/drivers/net/wireless/intersil/hostap/hostap_hw.c
index 6df3ee561d52..6dbf8ee9490a 100644
--- a/drivers/net/wireless/intersil/hostap/hostap_hw.c
+++ b/drivers/net/wireless/intersil/hostap/hostap_hw.c
@@ -839,12 +839,15 @@ static int hfa384x_get_rid(struct net_device *dev, u16 rid, void *buf, int len,
 	if (!res)
 		res = hfa384x_from_bap(dev, BAP0, &rec, sizeof(rec));
 
-	if (le16_to_cpu(rec.len) == 0) {
-		/* RID not available */
-		res = -ENODATA;
+	if (!res) {
+		if (le16_to_cpu(rec.len) == 0) {
+			/* RID not available */
+			res = -ENODATA;
+		}
+
+		rlen = (le16_to_cpu(rec.len) - 1) * 2;
 	}
 
-	rlen = (le16_to_cpu(rec.len) - 1) * 2;
 	if (!res && exact_len && rlen != len) {
 		printk(KERN_DEBUG "%s: hfa384x_get_rid - RID len mismatch: "
 		       "rid=0x%04x, len=%d (expected %d)\n",
-- 
2.7.0

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#1319480 — Re: [PATCH] hostap: avoid uninitialized variable use in hfa384x_get_rid

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);

?

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

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