commit 1f1cc456 upstream.

The current line offset validation is off by one. Depending on the data
stored behind the descs array this can either cause undefined behavior or
disclose arbitrary, potentially sensitive, memory to the issuing userspace
application.

Make sure that offset is within the bounds of the desc array.

Fixes: 521a2ad6 ("gpio: add userspace ABI for GPIO line information")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>