fix wrong parameter size on ioctl FIONREAD

fix wrong parameter size on ioctl FIONREAD

On Wed, Sep 23, 2009 at 23:11, Matthias Schwarzott <zzam@gentoo.org> wrote:
> It is about ioctl failures on amd64:
>   http://bugs.gentoo.org/show_bug.cgi?id=286041
>
> A bad parameter type to an ioctl() call causes udev-146 to generate "error
> getting buffer for inotify" messages in syslog.  The offending code is
> roughly:
>
>    ssize_t nbytes, pos;
>    // ...
>    ioctl(fd, FIONREAD, &nbytes);
>
> where ssize_t is 64 bits on amd64, but the kernel code for FIONREAD (at least
> through gentoo-sources-2.6.31) uses type int:
>
>    p = (void __user *) arg;
>    switch (cmd) {
>    case FIONREAD:
>        // ...
>        ret = put_user(send_len, (int __user *) p);
>
> so the upper 32 bits of "nbytes" are left uninitialized, and the subsequent
> malloc(nbytes) fails unless those 32 bits happen to be zero (or the system has
> a LOT of memory).