gpiolib: cdev: annotate struct linereq with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct linereq.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
index e39d344feb28997696e7543edeaf30d9d18d5f05..31fc71a612c2d3b8a4cc047367310e0fe5a47409 100644 (file)
--- a/drivers/gpio/gpiolib-cdev.c
+++ b/drivers/gpio/gpiolib-cdev.c
@@ -572,7 +572,7 @@ struct linereq {
        DECLARE_KFIFO_PTR(events, struct gpio_v2_line_event);
        atomic_t seqno;
        struct mutex config_mutex;
-       struct line lines[];
+       struct line lines[] __counted_by(num_lines);
 };
 
 #define GPIO_V2_LINE_BIAS_FLAGS \
@@ -1656,6 +1656,7 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
        lr = kzalloc(struct_size(lr, lines, ulr.num_lines), GFP_KERNEL);
        if (!lr)
                return -ENOMEM;
+       lr->num_lines = ulr.num_lines;
 
        lr->gdev = gpio_device_get(gdev);
 
@@ -1684,7 +1685,6 @@ static int linereq_create(struct gpio_device *gdev, void __user *ip)
                lr->event_buffer_size = GPIO_V2_LINES_MAX * 16;
 
        atomic_set(&lr->seqno, 0);
-       lr->num_lines = ulr.num_lines;
 
        /* Request each GPIO */
        for (i = 0; i < ulr.num_lines; i++) {