USB: yurex: Check for truncation in yurex_read()

[ Upstream commit 14427b86837a4baf1c121934c6599bdb67dfa9fc ]

snprintf() always returns the full length of the string it could have
printed, even if it was truncated because the buffer was too small.
So in case the counter value is truncated, we will over-read from
in_buffer and over-write to the caller's buffer.

I don't think it's actually possible for this to happen, but in case
truncation occurs, WARN and return -EIO.

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c
index 0673f286afbd4abb3a360540c3c95dae6237a078..4f48f5730e12664ecffd6b2c2cbecf8ad98aca43 100644 (file)
--- a/drivers/usb/misc/yurex.c
+++ b/drivers/usb/misc/yurex.c
@@ -417,6 +417,9 @@ static ssize_t yurex_read(struct file *file, char __user *buffer, size_t count,
        spin_unlock_irqrestore(&dev->lock, flags);
        mutex_unlock(&dev->io_mutex);
 
+       if (WARN_ON_ONCE(len >= sizeof(in_buffer)))
+               return -EIO;
+
        return simple_read_from_buffer(buffer, count, ppos, in_buffer, len);
 }