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USB: yurex: fix out-of-bounds uaccess in read handler
In general, accessing userspace memory beyond the length of the supplied
buffer in VFS read/write handlers can lead to both kernel memory corruption
(via kernel_read()/kernel_write(), which can e.g. be triggered via
sys_splice()) and privilege escalation inside userspace.

Fix it by using simple_read_from_buffer() instead of custom logic.

Fixes: 6bc235a ("USB: add driver for Meywa-Denki & Kayac YUREX")
Signed-off-by: Jann Horn <jannh@google.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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thejh authored and gregkh committed Jul 6, 2018
1 parent bba57ed commit f1e255d
Showing 1 changed file with 6 additions and 17 deletions.
23 changes: 6 additions & 17 deletions drivers/usb/misc/yurex.c
Expand Up @@ -396,35 +396,24 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count,
loff_t *ppos)
{
struct usb_yurex *dev;
int retval = 0;
int bytes_read = 0;
int len = 0;
char in_buffer[20];
unsigned long flags;

dev = file->private_data;

mutex_lock(&dev->io_mutex);
if (!dev->interface) { /* already disconnected */
retval = -ENODEV;
goto exit;
mutex_unlock(&dev->io_mutex);
return -ENODEV;
}

spin_lock_irqsave(&dev->lock, flags);
bytes_read = snprintf(in_buffer, 20, "%lld\n", dev->bbu);
len = snprintf(in_buffer, 20, "%lld\n", dev->bbu);
spin_unlock_irqrestore(&dev->lock, flags);

if (*ppos < bytes_read) {
if (copy_to_user(buffer, in_buffer + *ppos, bytes_read - *ppos))
retval = -EFAULT;
else {
retval = bytes_read - *ppos;
*ppos += bytes_read;
}
}

exit:
mutex_unlock(&dev->io_mutex);
return retval;

return simple_read_from_buffer(buffer, count, ppos, in_buffer, len);
}

static ssize_t yurex_write(struct file *file, const char __user *user_buffer,
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