[PATCH] usb: xhci: fix missing null termination after copy_from_user()

[Weigang He]

The buffer 'buf' is filled by copy_from_user() but is not properly
null-terminated before being used with strncmp(). If userspace provides
fewer than 10 bytes, strncmp() may read beyond the copied data into
uninitialized stack memory.

Add explicit null termination after copy_from_user() to ensure the
buffer is always a valid C string before string operations.

Fixes: 87a03802184c ("xhci: debugfs: add debugfs interface to enable compliance mode for a port")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Weigang He <geoffreyhe2@xxxxxxxxx>
---
 drivers/usb/host/xhci-debugfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci-debugfs.c b/drivers/usb/host/xhci-debugfs.c
index c1eb1036ede95..1e2350de77775 100644
--- a/drivers/usb/host/xhci-debugfs.c
+++ b/drivers/usb/host/xhci-debugfs.c
@@ -347,11 +347,13 @@ static ssize_t xhci_port_write(struct file *file,  const char __user *ubuf,
 	struct xhci_port	*port = s->private;
 	struct xhci_hcd		*xhci = hcd_to_xhci(port->rhub->hcd);
 	char                    buf[32];
+	size_t			len = min_t(size_t, sizeof(buf) - 1, count);
 	u32			portsc;
 	unsigned long		flags;
 
-	if (copy_from_user(&buf, ubuf, min_t(size_t, sizeof(buf) - 1, count)))
+	if (copy_from_user(&buf, ubuf, len))
 		return -EFAULT;
+	buf[len] = '\0';
 
 	if (!strncmp(buf, "compliance", 10)) {
 		/* If CTC is clear, compliance is enabled by default */
-- 
2.34.1