[libvirt] [PATCH 2/3] New utility functions virFileCreate and virDirCreate

[Serge E. Hallyn]

Quoting Laine Stump (laine at laine.org):
> These functions create a new file or directory with the given
> uid/gid. If the flag VIR_FILE_CREATE_AS_UID is given, they do this by
> forking a new process, calling setuid/setgid in the new process, and
> then creating the file. This is better than simply calling open then
> fchown, because in the latter case, a root-squashing nfs server would
> create the new file as user nobody, then refuse to allow fchown.
> 
> If VIR_FILE_CREATE_AS_UID is not specified, the simpler tactic of
> creating the file/dir, then chowning is is used. This gives better
> results in cases where the parent directory isn't on a root-squashing
> NFS server, but doesn't give permission for the specified uid/gid to
> create files. (Note that if the fork/setuid method fails to create the
> file due to access privileges, the parent process will make a second
> attempt using this simpler method.)
> 
> Return from both of these functions is 0 on success, or the value of
> errno if there was a failure.
> ---
>  src/util/util.c |  247 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  src/util/util.h |    9 ++
>  2 files changed, 256 insertions(+), 0 deletions(-)
> 
> diff --git a/src/util/util.c b/src/util/util.c
> index 1d493de..1cb29f4 100644
> --- a/src/util/util.c
> +++ b/src/util/util.c
> @@ -1126,6 +1126,253 @@ int virFileExists(const char *path)
>      return(0);
>  }
> 
> +
> +static int virFileCreateSimple(const char *path, mode_t mode, uid_t uid, gid_t gid) {
> +    int fd = -1;
> +    int ret = 0;
> +
> +    if ((fd = open(path, O_RDWR | O_CREAT | O_EXCL, mode)) < 0) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno, _("failed to create file '%s'"),
> +                             path);
> +        goto error;
> +    }
> +    if ((getuid() == 0) && ((uid != 0) || (gid != 0))) {

How about checking for CAP_CHOWN instead of getuid()==0?  Otherwise
if I try installing this certain ways, virFileCreateSimple() will refuse
to try the chown even though it could succeed.

-serge