Re: [PATCH 7/7] [v2] drivers/misc: introduce Freescale hypervisor management driver

On Wed, 1 Jun 2011 20:46:18 +0100
Alan Cox [off-list ref] wrote:

quoted

+static char *strdup_from_user(const char __user *ustr, size_t max)
+{
+	size_t len;
+	char *str;
+
+	len = strnlen_user(ustr, max);
+	if (len > max)
+		return ERR_PTR(-ENAMETOOLONG);

if (len >= max)

quoted

+	str = kmalloc(len, GFP_KERNEL);
+	if (!str)
+		return ERR_PTR(-ENOMEM);
+
+	if (copy_from_user(str, ustr, len))
+		return ERR_PTR(-EFAULT);
+
+	return str;
+}

Memory leak on the EFAULT path

If strnlen_user gets an exception, it'll return zero, causing a
zero-length kmalloc.  Will kmalloc(0, ...) return NULL?  If so, a bad
user pointer would result in -ENOMEM rather than -EFAULT.

quoted

+	default:
+		pr_debug("fsl-hv: unknown ioctl %u\n", cmd);
+		ret = -ENOIOCTLCMD;

-ENOTTY

(-ENOIOCTLCMD is an internal indicator designed so driver layers can say
'dunno, try the next layer up')

There's a check for -ENOIOCTLCMD in vfs_ioctl() -- though it generates
-EINVAL rather than -ENOTTY (why?).

Using -ENOIOCTLCMD consistently would make it easier to refactor a
toplevel ioctl handler into a nested one, plus consistency is good in
general.

quoted

+ * We use the same interrupt handler for all doorbells.  Whenever a doorbell
+ * is rung, and we receive an interrupt, we just put the handle for that
+ * doorbell (passed to us as *data) into all of the queues.

I wonder if these should be presented as IRQs or whether that makes no
sense ?

They are presented as IRQs.  This driver registers the same handler for all
doorbell IRQs, and pipes the notifications up to userspace, but you could
also directly register a kernel handler for an individual doorbell IRQ.

quoted

+static irqreturn_t fsl_hv_shutdown_isr(int irq, void *data)
+{
+	schedule_work(&power_off);
+
+	/* We should never get here */

Probably worth printing something if you do (panic(...) ?)

I don't think the comment is accurate.  We've just scheduled the workqueue,
not waited for it to complete.

Timur, shouldn't this schedule orderly_poweroff rather than
kernel_power_off?

-Scott