4.4-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
commit f1e255d60ae66a9f672ff9a207ee6cd8e33d2679 upstream.
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: 6bc235a2e24a ("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
--- drivers/usb/misc/yurex.c | 23 ++++++----------------- 1 file changed, 6 insertions(+), 17 deletions(-)
--- a/drivers/usb/misc/yurex.c +++ b/drivers/usb/misc/yurex.c @@ -414,8 +414,7 @@ static ssize_t yurex_read(struct file *f loff_t *ppos) { struct usb_yurex *dev; - int retval = 0; - int bytes_read = 0; + int len = 0; char in_buffer[20]; unsigned long flags;
@@ -423,26 +422,16 @@ static ssize_t yurex_read(struct file *f
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,