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@xxxxxxxxxx>
---
drivers/usb/misc/yurex.c | 23 ++++++-----------------
1 file changed, 6 insertions(+), 17 deletions(-)
diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c
index 8abb6cbbd98a..3be40eaa1ac9 100644
--- a/drivers/usb/misc/yurex.c
+++ b/drivers/usb/misc/yurex.c
@@ -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,
--
2.18.0.399.gad0ab374a1-goog
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