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    SubjectRe: [PATCH 7/7] [v2] drivers/misc: introduce Freescale hypervisor management driver
    On Wed, 1 Jun 2011 20:46:18 +0100
    Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

    > > +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)

    > > + 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.

    > > + 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.

    > > + * 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.

    > > +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



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