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Subject[PATCH 3.18 03/29] USB: yurex: fix out-of-bounds uaccess in read handler
Date
3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

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
@@ -413,8 +413,7 @@ static int yurex_release(struct inode *i
static ssize_t yurex_read(struct file *file, char *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;

@@ -422,26 +421,16 @@ 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_buffer, size_t count, loff_t *ppos)

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