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Re: [libvirt] [PATCH v2] storage: Check for invalid storage mode before opening



On 05/24/2010 06:36 AM, Daniel P. Berrange wrote:
> On Fri, May 21, 2010 at 02:24:24PM -0400, Cole Robinson wrote:
>> On 05/21/2010 02:17 PM, Eric Blake wrote:
>>> On 05/21/2010 11:03 AM, Cole Robinson wrote:
>>>> If a directory pool contains pipes or sockets, a pool start can fail or hang:
>>>>
>>>> https://bugzilla.redhat.com/show_bug.cgi?id=589577
>>>>
>>>> We already try to avoid these special files, but only attempt after
>>>> opening the path, which is where the problems lie. Unify volume opening
>>>> into a single function which runs stat() before any open() call. Directory
>>>
>>> This sentence of the commit log is out-of-date...
>>>
>>>> pools can then proceed along, ignoring the invalid files.
>>>>
>>>> v2: Use ATTRIBUTE_NONNULL. Drop stat check, just open with
>>>>     O_NONBLOCK|O_NOCTTY.
>>>
>>> ...given this sentence.
>>>
>>>> +int
>>>> +virStorageBackendVolOpen(const char *path)
>>>> +{
>>>> +    int fd;
>>>> +
>>>> +    if ((fd = open(path, O_RDONLY|O_NONBLOCK|O_NOCTTY)) < 0) {
>>>> +        virReportSystemError(errno,
>>>> +                             _("cannot open volume '%s'"),
>>>> +                             path);
>>>> +        return -1;
>>>> +    }
>>>
>>> I'm thinking that we still want to use fstat() (after the open()) and
>>> reject directories, sockets, and pipes (or more accurately, accept only
>>> regular files, block devices, and possibly character devices).
>>>
>>> In other words, you got rid of the stat/open race (good), but also got
>>> rid of the strictness provided by validating [f]stat (not so good).
>>>
>>
>> Sorry, I should have pointed out that there is already code that does
>> this, see virStorageBackendUpdateVolTargetInfoFD, which is always called
>> after VolOpen. The existing code is all confusingly arranged though, so
>> maybe I should take a harder look at organizing.
> 
> That check isn't sufficient. We need to explicitly *allow* directories
> to be reported, since a pool may point at a directory containing trees
> for container based virt root filesystems. We should drop block+char
> devices for directory based pools too, since those aren't relevant,
> being dealt with by other storage pool backends.
> 

I've sent an updated patch, but I only copied the existing mode checks
from virStorageBackendUpdateVolTargetInfoFD, so these points aren't
addressed. They will take a bit more surgery then I expected, since
volumes are opened via several different code paths.

- Cole


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