Re: [PATCH 06/11] compat_ioctl: remove /dev/random commands

[Al Viro]

On Sat, Sep 08, 2018 at 04:28:12PM +0200, Arnd Bergmann wrote:
> These are all handled by the random driver, so instead of listing
> each ioctl, we can just use the same function to deal with both
> native and compat commands.

Umm...  I don't think it's right -

>       .unlocked_ioctl = random_ioctl,
> +     .compat_ioctl = random_ioctl,


->compat_ioctl() gets called in
                        error = f.file->f_op->compat_ioctl(f.file, cmd, arg);
so you do *NOT* get compat_ptr() for those - they have to do it on their
own.  It's not hard to provide a proper compat_ioctl() instance for that
one, but this is not it.  What you need in drivers/char/random.c part of
that one is something like

diff --git a/drivers/char/random.c b/drivers/char/random.c
index bf5f99fc36f1..1de75c784cf6 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1954,10 +1954,9 @@ static ssize_t random_write(struct file *file, const 
char __user *buffer,
        return (ssize_t)count;
 }
 
-static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
+static long __random_ioctl(struct file *f, unsigned int cmd, int __user *p)
 {
        int size, ent_count;
-       int __user *p = (int __user *)arg;
        int retval;
 
        switch (cmd) {
@@ -2011,6 +2010,18 @@ static long random_ioctl(struct file *f, unsigned int 
cmd, unsigned long arg)
        }
 }
 
+static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
+{
+       return __random_ioctl(f, cmd, (int __user *)arg);
+}
+
+#ifdef CONFIG_COMPAT
+static long compat_random_ioctl(struct file *f, unsigned int cmd, unsigned 
long arg)
+{
+       return __random_ioctl(f, cmd, compat_ptr(arg));
+}
+#endif
+
 static int random_fasync(int fd, struct file *filp, int on)
 {
        return fasync_helper(fd, filp, on, &fasync);
@@ -2021,6 +2032,9 @@ const struct file_operations random_fops = {
        .write = random_write,
        .poll  = random_poll,
        .unlocked_ioctl = random_ioctl,
+#ifdef CONFIG_COMPAT
+       .compat_ioctl = compat_random_ioctl,
+#endif
        .fasync = random_fasync,
        .llseek = noop_llseek,
 };