[PATCH] ethtool: fix ethtool_get_regs() to work with zero length registers

cfg80211 exports zero length register size as it currently only uses
struct ethtool_regs.version to export struct wiphy.hw_version. But the
problem is that ethtool_get_regs() assumes that the driver (cfg80211 in this
case) always has non-zero length for registers. With cfg80211
it would always fail and return -ENOMEM to user space.

Fix this by checking the register length from the driver and exporting
struct ethtool_regs to user space if the length is zero.

With this patch it's possible to get the hardware id from wireless drivers.
Tested with wl12xx and ath6kl.

Tested-by: Gery Kahn <redacted>
Signed-off-by: Kalle Valo <redacted>
---
 net/core/ethtool.c |   20 +++++++++++++-------
 1 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index fd14116..6f073f4 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c

@@ -1213,7 +1213,7 @@ static int ethtool_get_regs(struct net_device *dev, char __user *useraddr)
 {
 	struct ethtool_regs regs;
 	const struct ethtool_ops *ops = dev->ethtool_ops;
-	void *regbuf;
+	void *regbuf = NULL;
 	int reglen, ret;
 
 	if (!ops->get_regs || !ops->get_regs_len)

@@ -1226,18 +1226,24 @@ static int ethtool_get_regs(struct net_device *dev, char __user *useraddr)
 	if (regs.len > reglen)
 		regs.len = reglen;
 
-	regbuf = vzalloc(reglen);
-	if (!regbuf)
-		return -ENOMEM;
+	if (reglen > 0) {
+		regbuf = vzalloc(reglen);
+		if (!regbuf)
+			return -ENOMEM;
+	}
 
 	ops->get_regs(dev, &regs, regbuf);
 
 	ret = -EFAULT;
 	if (copy_to_user(useraddr, &regs, sizeof(regs)))
 		goto out;
-	useraddr += offsetof(struct ethtool_regs, data);
-	if (copy_to_user(useraddr, regbuf, regs.len))
-		goto out;
+
+	if (regs.len > 0) {
+		useraddr += offsetof(struct ethtool_regs, data);
+		if (copy_to_user(useraddr, regbuf, regs.len))
+			goto out;
+	}
+
 	ret = 0;
 
  out:

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On Wed, 2011-07-20 at 12:18 +0300, Kalle Valo wrote:

cfg80211 exports zero length register size as it currently only uses
struct ethtool_regs.version to export struct wiphy.hw_version.

[...]

The ethtool_regs::version field represents the version of the register
dump format.  This may or may not relate to a hardware version.

If you don't actually provide a register dump then don't implement this
operation.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

On 07/20/2011 02:38 PM, Ben Hutchings wrote:

On Wed, 2011-07-20 at 12:18 +0300, Kalle Valo wrote:

quoted

cfg80211 exports zero length register size as it currently only uses
struct ethtool_regs.version to export struct wiphy.hw_version.

[...]

The ethtool_regs::version field represents the version of the register
dump format.  This may or may not relate to a hardware version.

If you don't actually provide a register dump then don't implement this
operation.

Then we have a problem as cfg80211 exports the hw version without any
register dumps:

static int cfg80211_get_regs_len(struct net_device *dev)
{
	/* For now, return 0... */
	return 0;
}

static void cfg80211_get_regs(struct net_device *dev, struct
ethtool_regs *regs,
			void *data)
{
	struct wireless_dev *wdev = dev->ieee80211_ptr;

	regs->version = wdev->wiphy->hw_version;
	regs->len = 0;
}

And this has been there a long time already. How cfg80211 should export
hw version if this is not a proper way?

Kalle
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