Re: [Qemu-devel] [PATCH 2/3] block: Add support to "open" /dev/fd/X filenames

[Eric Blake <eblake@redhat.com>]

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On 06/04/2012 07:10 AM, Corey Bryant wrote:
> The main goal of this patch series is to enable isolation of guest
> images that are stored on the same NFS mount.  This can be achieved
> if the management application opens files for QEMU, and QEMU is
> restricted from opening files.
> 
> This patch adds support to the block layer open paths to dup(X) a
> pre-opened file descriptor if the filename is of the format
> /dev/fd/X.
> 
> One nice thing about this approach is that no new SELinux policy is
> required to prevent open of NFS files (files with type nfs_t).  The
> virt_use_nfs boolean type simply needs to be set to false, and open
> will be prevented (yet dup will be allowed).  For example:
> 
>   # setsebool virt_use_nfs 0
>   # getsebool virt_use_nfs
>   virt_use_nfs --> off
> 
> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>

>  
> +int file_open(const char *filename, int flags, mode_t mode)
> +{
> +#ifndef _WIN32
> +    int fd;
> +    const char *p;
> +
> +    if (strstart(filename, "/dev/fd/", &p)) {
> +        fd = atoi(p);

atoi() is lousy - it has no error checking, and returns 0 if a mistake
was made.  You really want to be using strtol (or even better, a
sensible wrapper around strtol that takes care of the subtleties of
calling it correctly), so that you don't end up dup'ing stdin when the
user passes a bad /dev/fd/ string.

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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