[PATCH 4.9 17/36] gpioib: do not free unrequested descriptors

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Timur Tabi <timur@codeaurora.org>

commit ab3dbcf78f60f46d6a0ad63b1f4b690b7a427140 upstream.

If the main loop in linehandle_create() encounters an error, it
unwinds completely by freeing all previously requested GPIO
descriptors.  However, if the error occurs in the beginning of
the loop before that GPIO is requested, then the exit code
attempts to free a null descriptor.  If extrachecks is enabled,
gpiod_free() triggers a WARN_ON.

Instead, keep a separate count of legitimate GPIOs so that only
those are freed.

Cc: stable@vger.kernel.org
Fixes: d7c51b47ac11 ("gpio: userspace ABI for reading/writing GPIO lines")
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpio/gpiolib.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -425,7 +425,7 @@ static int linehandle_create(struct gpio
 	struct gpiohandle_request handlereq;
 	struct linehandle_state *lh;
 	struct file *file;
-	int fd, i, ret;
+	int fd, i, count = 0, ret;
 
 	if (copy_from_user(&handlereq, ip, sizeof(handlereq)))
 		return -EFAULT;
@@ -471,6 +471,7 @@ static int linehandle_create(struct gpio
 		if (ret)
 			goto out_free_descs;
 		lh->descs[i] = desc;
+		count = i;
 
 		if (lflags & GPIOHANDLE_REQUEST_ACTIVE_LOW)
 			set_bit(FLAG_ACTIVE_LOW, &desc->flags);
@@ -537,7 +538,7 @@ static int linehandle_create(struct gpio
 out_put_unused_fd:
 	put_unused_fd(fd);
 out_free_descs:
-	for (; i >= 0; i--)
+	for (i = 0; i < count; i++)
 		gpiod_free(lh->descs[i]);
 	kfree(lh->label);
 out_free_lh: