of/device: Prevent buffer overflow in of_device_modalias()

As of_device_get_modalias() returns the number of bytes that would have
been written to the target string, regardless of how much did fit in the
buffer, it's possible that the returned index points beyond the buffer
passed to of_device_modalias() - causing memory beyond the buffer to be
null terminated.

Fixes: 0634c2958927 ("of: Add function for generating a DT modalias with a newline")
Cc: Rob Herring <robh@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>

diff --git a/drivers/of/device.c b/drivers/of/device.c
index 9d0895fb53b5a743fec6b76dab25c8232da5f293..c5c06997fdd2a13f07bef147df12b09365c117a9 100644 (file)
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -257,6 +257,8 @@ ssize_t of_device_modalias(struct device *dev, char *str, ssize_t len)
        ssize_t sl = of_device_get_modalias(dev, str, len - 2);
        if (sl < 0)
                return sl;
+       if (sl > len - 2)
+               return -ENOMEM;
 
        str[sl++] = '\n';
        str[sl] = 0;