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Re: [libvirt] [PATCH 3/3] storage: Check for invalid storage mode before opening



On 05/20/2010 06:25 PM, Eric Blake wrote:
> On 05/20/2010 01:23 PM, 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
>> pools can then proceed along, ignoring the invalid files.
> 
> stat() before open() is racy.  Better yet is using the
> O_NONBLOCK|O_NOCTTY flags of open(); gnulib guarantees they are defined,
> and I recently lobbied POSIX to guarantee that it will be safe on all
> platforms (it is already safe on Linux):
> http://austingroupbugs.net/view.php?id=141
> 
>>  
>> +int
>> +virStorageBackendVolOpen(const char *path)
>> +{
>> +    int fd;
>> +    struct stat sb;
>> +
>> +    if (stat(path, &sb) < 0) {
>> +        virReportSystemError(errno,
>> +                             _("cannot stat file '%s'"), path);
>> +        return -1;
>> +    }
>> +
>> +    if (!S_ISREG(sb.st_mode) &&
>> +        !S_ISCHR(sb.st_mode) &&
>> +        !S_ISBLK(sb.st_mode)) {
> 
> Regular files and block devices I can understand, but character devices?
>  That includes things like /dev/zero and /dev/null; do those really make
> sense as the backing of a volume store?
> 

Not sure honestly, this chunk was copied from other code which already
did the fstat check (just wasn't early enough or so I thought).

>> +        VIR_DEBUG("Skipping volume path %s, unexpected file mode.", path);
>> +        return -2;
>> +    }
>> +
>> +    if ((fd = open(path, O_RDONLY)) < 0) {
>> +        virReportSystemError(errno,
>> +                             _("cannot open volume '%s'"),
>> +                             path);
> 
> In other words, I'd rather see open(path,O_RDONLY|O_NONBLOCK|O_NOCTTY)
> then fstat(), and not your stat()/open() sequence.
> 
> But the rest of the patch looks sane.
> 

Seems to get the job done, updated patch resent.

Thanks,
Cole


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