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



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?

> +        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.

-- 
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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