USB: yurex: Check for truncation in yurex_read()

BugLink: https://bugs.launchpad.net/bugs/1836426
[ 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>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/drivers/usb/misc/yurex.c b/drivers/usb/misc/yurex.c
index 1232dd49556d29b00af98c347d0515c9ae91cbc7..6d9fd5f649036e8fb47c39eaeffa26f856724e99 100644 (file)
--- a/drivers/usb/misc/yurex.c
+++ b/drivers/usb/misc/yurex.c
@@ -413,6 +413,9 @@ 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);
 }