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



On Wed, Jan 13, 2010 at 01:25:06AM -0500, Laine Stump wrote:
> 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))) {
> +        if (fchown(fd, uid, gid) < 0) {
> +            ret = errno;
> +            virReportSystemError(NULL, errno, _("cannot chown '%s' to (%u, %u)"),
> +                                 path, uid, gid);
> +            close(fd);
> +            goto error;
> +        }
> +    }
> +    if (close(fd) < 0) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno, _("failed to close new file '%s'"),
> +                             path);
> +        goto error;
> +    }
> +    fd = -1;
> +error:
> +    return ret;
> +}
> +
> +static int virDirCreateSimple(const char *path, mode_t mode, uid_t uid, gid_t gid) {
> +    int ret = 0;
> +
> +    if (mkdir(path, mode) < 0) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno, _("failed to create directory '%s'"),
> +                             path);
> +        goto error;
> +    }
> +
> +    if ((getuid() == 0) && ((uid != 0) || (gid != getgid()))) {
> +        if (chown(path, uid, gid) < 0) {
> +            ret = errno;
> +            virReportSystemError(NULL, errno, _("cannot chown '%s' to (%u, %u)"),
> +                                 path, uid, gid);
> +            goto error;
> +        }
> +    }
> +error:
> +    return ret;
> +}
> +
> +#ifndef WIN32
> +int virFileCreate(const char *path, mode_t mode,
> +                  uid_t uid, gid_t gid, unsigned int flags) {
> +    pid_t pid;
> +    int waitret, status, ret = 0;
> +    int fd = -1;
> +
> +    if ((!(flags & VIR_FILE_CREATE_AS_UID))
> +        || (getuid() != 0)
> +        || ((uid == 0) && (gid == 0))) {
> +        return virFileCreateSimple(path, mode, uid, gid);
> +    }
> +
> +    /* parent is running as root, but caller requested that the
> +     * file be created as some other user and/or group). The
> +     * following dance avoids problems caused by root-squashing
> +     * NFS servers. */
> +
> +    if ((pid = fork()) < 0) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno,
> +                             _("cannot fork o create file '%s'"), path);
> +        return ret;
> +    }
> +
> +    if (pid) { /* parent */
> +        /* wait for child to complete, and retrieve its exit code */
> +        while ((waitret = waitpid(pid, &status, 0) == -1)
> +               && (errno == EINTR));
> +        if (waitret == -1) {
> +            ret = errno;
> +            virReportSystemError(NULL, errno,
> +                                 _("failed to wait for child creating '%s'"),
> +                                 path);
> +            return ret;
> +        }
> +        ret = WEXITSTATUS(status);
> +        if (!WIFEXITED(status) || (ret == EACCES)) {
> +            /* fall back to the simpler method, which works better in
> +             * some cases */
> +            /* Should we log a warning here? */
> +            return virFileCreateSimple(path, mode, uid, gid);
> +        }
> +        if ((ret == 0) && (gid != 0)) {
> +            /* check if group was set properly by creating after
> +             * setgid. If not, try doing it with chown */
> +            struct stat st;
> +            if (stat(path, &st) == -1) {
> +                ret = errno;
> +                virReportSystemError(NULL, errno,
> +                                     _("stat of '%s' failed"),
> +                                     path);
> +                return ret;
> +            }
> +            if ((st.st_gid != gid) && (chown(path, -1, gid) < 0)) {
> +                ret = errno;
> +                virReportSystemError(NULL, errno, _("cannot chown '%s' to group %u"),
> +                                     path, gid);
> +            }
> +        }
> +        return ret;
> +    }
> +
> +    /* child - set desired uid/gid, then attempt to create the file */
> +
> +    if ((gid != 0) && (setgid(gid) != 0)) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno, _("cannot set gid %u creating '%s'"),
> +                             gid, path);
> +        goto childerror;
> +    }
> +    if  ((uid != 0) && (setuid(uid) != 0)) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno, _("cannot set uid %u creating '%s'"),
> +                             uid, path);
> +        goto childerror;
> +    }
> +    if ((fd = open(path, O_RDWR | O_CREAT | O_EXCL, mode)) < 0) {
> +        ret = errno;
> +        if (ret != EACCES) {
> +            /* in case of EACCES, the parent will retry */
> +            virReportSystemError(NULL, errno, _("child failed to create file '%s'"),
> +                                 path);
> +        }
> +        goto childerror;
> +    }
> +    if (close(fd) < 0) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno, _("child failed to close new file '%s'"),
> +                             path);
> +        goto childerror;
> +    }
> +childerror:
> +    _exit(ret);
> +
> +}
> +
> +int virDirCreate(const char *path, mode_t mode,
> +                 uid_t uid, gid_t gid, unsigned int flags) {
> +    pid_t pid;
> +    int waitret;
> +    int status, ret = 0;
> +
> +    if ((!(flags & VIR_FILE_CREATE_AS_UID))
> +        || (getuid() != 0)
> +        || ((uid == 0) && (gid == 0))) {
> +        return virDirCreateSimple(path, mode, uid, gid);
> +    }
> +
> +    if ((pid = fork()) < 0) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno,
> +                             _("cannot fork to create directory '%s'"),
> +                             path);
> +        return ret;
> +    }
> +
> +    if (pid) { /* parent */
> +        /* wait for child to complete, and retrieve its exit code */
> +        while ((waitret = waitpid(pid, &status, 0) == -1)  && (errno == EINTR));
> +        if (waitret == -1) {
> +            ret = errno;
> +            virReportSystemError(NULL, errno,
> +                                 _("failed to wait for child creating '%s'"),
> +                                 path);
> +            return ret;
> +        }
> +        ret = WEXITSTATUS(status);
> +        if (!WIFEXITED(status) || (ret == EACCES)) {
> +            /* fall back to the simpler method, which works better in some cases */
> +            /* Should we log a warning here? */
> +            return virDirCreateSimple(path, mode, uid, gid);
> +        }
> +        if ((ret == 0) && (gid != 0)) {
> +            /* check if group was set properly by creating after
> +             * setgid. If not, try doing it with chown */
> +            struct stat st;
> +            if (stat(path, &st) == -1) {
> +                ret = errno;
> +                virReportSystemError(NULL, errno,
> +                                     _("stat of '%s' failed"),
> +                                     path);
> +                return ret;
> +            }
> +            if ((st.st_gid != gid) && (chown(path, -1, gid) < 0)) {
> +                ret = errno;
> +                virReportSystemError(NULL, errno, _("cannot chown '%s' to group %u"),
> +                                     path, gid);
> +            }
> +        }
> +
> +        return ret;
> +    }
> +
> +    /* child - set desired uid/gid, then attempt to create the directory */
> +
> +    if ((gid != 0) && (setgid(gid) != 0)) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno, _("cannot set gid %u creating '%s'"),
> +                             gid, path);
> +        goto childerror;
> +    }
> +    if  ((uid != 0) && (setuid(uid) != 0)) {
> +        ret = errno;
> +        virReportSystemError(NULL, errno, _("cannot set uid %u creating '%s'"),
> +                             uid, path);
> +        goto childerror;
> +    }
> +    if (mkdir(path, mode) < 0) {
> +        ret = errno;
> +        if (ret != EACCES) {
> +            /* in case of EACCES, the parent will retry */
> +            virReportSystemError(NULL, errno, _("child failed to create directory '%s'"),
> +                                 path);
> +        }
> +        goto childerror;
> +    }
> +childerror:
> +    _exit(ret);
> +}
> +
> +#else /* WIN32 */
> +
> +int virFileCreate(const char *path, mode_t mode,
> +                  uid_t uid, gid_t gid, unsigned int flags) {
> +    return virFileCreateSimple(path, mode, uid, gid);
> +}
> +
> +int virDirCreate(const char *path, mode_t mode,
> +                 uid_t uid, gid_t gid, unsigned int flags) {
> +    return virDirCreateSimple(path, mode, uid, gid);
> +}
> +#endif
> +
>  int virFileMakePath(const char *path)
>  {
>      struct stat st;
> diff --git a/src/util/util.h b/src/util/util.h
> index 5e70038..2762862 100644
> --- a/src/util/util.h
> +++ b/src/util/util.h
> @@ -111,6 +111,15 @@ char *virFindFileInPath(const char *file);
>  
>  int virFileExists(const char *path);
>  
> +enum {
> +    VIR_FILE_CREATE_NONE   = 0,
> +    VIR_FILE_CREATE_AS_UID = (1 << 0),
> +};
> +
> +int virFileCreate(const char *path, mode_t mode, uid_t uid, gid_t gid,
> +                  unsigned int flags) ATTRIBUTE_RETURN_CHECK;
> +int virDirCreate(const char *path, mode_t mode, uid_t uid, gid_t gid,
> +                 unsigned int flags) ATTRIBUTE_RETURN_CHECK;
>  int virFileMakePath(const char *path) ATTRIBUTE_RETURN_CHECK;
>  
>  int virFileBuildPath(const char *dir,

ACK

Daniel
-- 
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