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

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Message-ID: <1487659710.2096.1.camel@lesbg.com>
Date:   Tue, 21 Feb 2017 08:48:30 +0200
From:   Jonathan Dieter <jdieter@...bg.com>
To:     Krzysztof Opasiak <k.opasiak@...sung.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

Thanks for looking at this.  One quick question before I put out
version two with your corrections:

On Tue, 2017-02-21 at 07:12 +0100, Krzysztof Opasiak wrote:
> 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);

Should I also change the error messages to use real values?
Ex:
		err("busid length %i >= %i", size, sizeof(busid));

> > +		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,