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

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

On 06/04/2012 10:32 AM, Eric Blake wrote:
> 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.
>

It looks like strtol returns 0 on failure too.  Do we need to support 
stdin/stdout/stderr?

-- 
Regards,
Corey