[libvirt] [PATCH] node_device_driver.c: don't write beyond EOB for 4K-byte symlink

[Chris Lalancette]

On 12/14/2009 02:48 PM, Jim Meyering wrote:
> From: Jim Meyering <meyering at redhat.com>
> Date: Mon, 14 Dec 2009 12:05:38 +0100
> Subject: [PATCH] node_device_driver.c: don't write beyond EOB for 4K-byte symlink
> 
> * src/node_device/node_device_driver.c (update_driver_name): The
> previous code would write one byte beyond the end of the 4KiB
> stack buffer when presented with a symlink value of exactly that
> length (very unlikely).  Remove the automatic buffer and use
> virFileResolveLink in place of readlink.  Suggested by Daniel Veillard.
> ---
>  src/node_device/node_device_driver.c |    7 +++----
>  1 files changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/src/node_device/node_device_driver.c b/src/node_device/node_device_driver.c
> index f083f16..ecbac0f 100644
> --- a/src/node_device/node_device_driver.c
> +++ b/src/node_device/node_device_driver.c
> @@ -78,10 +78,9 @@ static int update_driver_name(virConnectPtr conn,
>                                virNodeDeviceObjPtr dev)
>  {
>      char *driver_link = NULL;
> -    char devpath[PATH_MAX];
> +    char *devpath;
>      char *p;
>      int ret = -1;
> -    int n;
> 
>      VIR_FREE(dev->def->driver);
> 
> @@ -97,12 +96,11 @@ static int update_driver_name(virConnectPtr conn,
>          goto cleanup;
>      }
> 
> -    if ((n = readlink(driver_link, devpath, sizeof devpath)) < 0) {
> +    if (virFileResolveLink(driver_link, &devpath) < 0) {

FYI; I found out today that virFileResolveLink() doesn't work on filesystems
backed by sysfs (which unfortunately this code path is).  The problem is that
sysfs doesn't follow the POSIX-specified behavior of placing the size
of the name of the real path in st.st_size; instead, on sysfs, st.st_size for
symlinks is *always* 0 (at least on my F-12 box here).  So this code path is
probably broken now.  DV said he will take a look at putting a patch together
to make virFileResolveLink() handle the 0 case.

-- 
Chris Lalancette