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USB: yurex: fix out-of-bounds uaccess in read handler

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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: 6bc235a2e2 ("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>
This commit is contained in:
Jann Horn 2018-07-06 17:12:56 +02:00 committed by Greg Kroah-Hartman
parent bba57eddad
commit f1e255d60a
1 changed files with 6 additions and 17 deletions
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23
drivers/usb/misc/yurex.c
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@ -396,8 +396,7 @@ 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;
@ -405,26 +404,16 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count,
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,