linux-kernel - Re: [PATCH 1/2] Fix format overflows

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Date:   Tue, 21 Feb 2017 07:12:27 +0100
From:   Krzysztof Opasiak <k.opasiak@...sung.com>
To:     Jonathan Dieter <jdieter@...bg.com>, linux-kernel@...r.kernel.org
Cc:     Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Peter Senna Tschudin <peter.senna@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:USB OVER IP DRIVER" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 1/2] Fix format overflows


Hi,

W dniu 2017-02-20 o 21:51, Jonathan Dieter pisze:
> The usbip userspace tools call sprintf()/snprintf() and don't check for
> the return value which can lead the paths to overflow, truncating the
> final file in the path.
>
> More urgently, GCC 7 now warns that these aren't checked with
> -Wformat-overflow, and with -Werror enabled in configure.ac, that makes
> these tools unbuildable.
>
> This patch fixes these problems by replacing sprintf() with snprintf() in
> one place and adding checks for the return value of snprintf().
>
> Reviewed-by: Peter Senna Tschudin <peter.senna@...il.com>
> Signed-off-by: Jonathan Dieter <jdieter@...bg.com>
> ---
>  tools/usb/usbip/libsrc/usbip_common.c      |  8 +++++++-
>  tools/usb/usbip/libsrc/usbip_host_common.c | 25 ++++++++++++++++++++-----
>  2 files changed, 27 insertions(+), 6 deletions(-)
>
> diff --git a/tools/usb/usbip/libsrc/usbip_common.c b/tools/usb/usbip/libsrc/usbip_common.c
> index ac73710..fc875ee 100644
> --- a/tools/usb/usbip/libsrc/usbip_common.c
> +++ b/tools/usb/usbip/libsrc/usbip_common.c
> @@ -215,9 +215,15 @@ int read_usb_interface(struct usbip_usb_device *udev, int i,
>  		       struct usbip_usb_interface *uinf)
>  {
>  	char busid[SYSFS_BUS_ID_SIZE];
> +	int size;
>  	struct udev_device *sif;
>
> -	sprintf(busid, "%s:%d.%d", udev->busid, udev->bConfigurationValue, i);
> +	size = snprintf(busid, SYSFS_BUS_ID_SIZE, "%s:%d.%d",

why not sizeof(busid)?

> +			udev->busid, udev->bConfigurationValue, i);
> +	if (size >= SYSFS_BUS_ID_SIZE) {

As above.

> +		err("busid length %i >= SYSFS_BUS_ID_SIZE", size);
> +		return -1;
> +	}
>
>  	sif = udev_device_new_from_subsystem_sysname(udev_context, "usb", busid);
>  	if (!sif) {
> diff --git a/tools/usb/usbip/libsrc/usbip_host_common.c b/tools/usb/usbip/libsrc/usbip_host_common.c
> index 9d41522..690cd49 100644
> --- a/tools/usb/usbip/libsrc/usbip_host_common.c
> +++ b/tools/usb/usbip/libsrc/usbip_host_common.c
> @@ -40,13 +40,19 @@ struct udev *udev_context;
>  static int32_t read_attr_usbip_status(struct usbip_usb_device *udev)
>  {
>  	char status_attr_path[SYSFS_PATH_MAX];
> +	int size;
>  	int fd;
>  	int length;
>  	char status;
>  	int value = 0;
>
> -	snprintf(status_attr_path, SYSFS_PATH_MAX, "%s/usbip_status",
> -		 udev->path);
> +	size = snprintf(status_attr_path, SYSFS_PATH_MAX, "%s/usbip_status",

The same here.

> +			udev->path);
> +	if (size >= SYSFS_PATH_MAX) {
> +		err("usbip_status path length %i >= SYSFS_PATH_MAX", size);
> +		return -1;
> +	}
> +
>
>  	fd = open(status_attr_path, O_RDONLY);
>  	if (fd < 0) {
> @@ -218,6 +224,7 @@ int usbip_export_device(struct usbip_exported_device *edev, int sockfd)
>  {
>  	char attr_name[] = "usbip_sockfd";
>  	char sockfd_attr_path[SYSFS_PATH_MAX];
> +	int size;
>  	char sockfd_buff[30];
>  	int ret;
>
> @@ -237,10 +244,18 @@ int usbip_export_device(struct usbip_exported_device *edev, int sockfd)
>  	}
>
>  	/* only the first interface is true */
> -	snprintf(sockfd_attr_path, sizeof(sockfd_attr_path), "%s/%s",
> -		 edev->udev.path, attr_name);
> +	size = snprintf(sockfd_attr_path, sizeof(sockfd_attr_path), "%s/%s",
> +			edev->udev.path, attr_name);
> +	if (size >= SYSFS_PATH_MAX) {

hmmm this should be sizeof(sockfd_attr_path) not SYSFS_PATH_MAX

> +		err("exported device path length %i >= SYSFS_PATH_MAX", size);
> +		return -1;
> +	}
>
> -	snprintf(sockfd_buff, sizeof(sockfd_buff), "%d\n", sockfd);
> +	size = snprintf(sockfd_buff, sizeof(sockfd_buff), "%d\n", sockfd);
> +	if (size >= 30) {

Please don't hardcode such values in if. use sizeof() like one line above

> +		err("socket length %i >= 30", size);
> +		return -1;
> +	}
>
>  	ret = write_sysfs_attribute(sockfd_attr_path, sockfd_buff,
>  				    strlen(sockfd_buff));
>

Best regards,
-- 
Krzysztof Opasiak
Samsung R&D Institute Poland
Samsung Electronics