[lxc-devel] Fwd: Re: [PATCH 2/2 v2] Update absolute paths for overlay and aufs mounts

Christian Brauner christianvanbrauner at gmail.com
Fri Oct 30 15:30:55 UTC 2015


---------- Forwarded message ----------
From: "Christian Brauner" <christianvanbrauner at gmail.com>
Date: Oct 30, 2015 4:27 PM
Subject: Re: [PATCH 2/2 v2] Update absolute paths for overlay and aufs
mounts
To: "Serge E. Hallyn" <serge.hallyn at ubuntu.com>
Cc: "lxc-dev" <lxc-devel at lists.linuxcontainers.org>

>
> On Oct 30, 2015 4:22 PM, "Serge Hallyn" <serge.hallyn at ubuntu.com> wrote:
> >
> > Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > > When using overlay and aufs mounts with lxc.mount.entry users have to
specify
> > > absolute paths for upperdir and workdir which will then get created
> > > automatically by mount_entry_create_overlay_dirs() and
> > > mount_entry_create_aufs_dirs() in conf.c. When we clone a container
with
> > > overlay or aufs lxc.mount.entry entries we need to update these
absolute paths.
> > > In order to do this we add the function
update_union_mount_entry_paths() in
> > > lxccontainer.c. The function updates the mounts in two locations:
> > >
> > >         1) lxc_conf->mount_list
> > >
> > > and
> > >
> > >         2) lxc_conf->unexpanded_config (by calling
clone_update_unexp_ovl_dir())
> > >
> > > If we were to only update 2) we would end up with wrong upperdir and
workdir
> > > mounts as the absolute paths would still point to the container that
serves as
> > > the base for the clone. If we were to only update 1) we would end up
with wrong
> > > upperdir and workdir lxc.mount.entry entries in the clone's config as
the
> > > absolute paths in upperdir and workdir would still point to the
container that
> > > serves as the base for the clone. Updating both will get the job done.
> > >
> > > NOTE: This function does not sanitize paths apart from removing
trailing
> > > slashes. (So when a user specifies //home//someone/// it will be
cleaned to
> > > //home//someone. This is the minimal path cleansing which is also
done by
> > > lxc_container_new().) But the mount_entry_create_overlay_dirs() and
> > > mount_entry_create_aufs_dirs() functions both try to be extremely
strict about
> > > when to create upperdirs and workdirs. They will only accept
sanitized paths,
> > > i.e. they require /home/someone. I think this is a (safety) virtue
and we
> > > should consider sanitizing paths in general. In short:
> > > update_union_mount_entry_paths() does update all absolute paths to
the new
> > > container but mount_entry_create_overlay_dirs() and
> > > mount_entry_create_aufs_dirs() will still refuse to create upperdir
and workdir
> > > when the updated path is unclean. This happens easily when e.g. a
user calls
> > > lxc-clone -o OLD -n NEW -P //home//chb///.
> > >
> > > Signed-off-by: Christian Brauner <christianvanbrauner at gmail.com>
> >
> > Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>
> >
> > > ---
> > >  src/lxc/lxccontainer.c | 97
++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 97 insertions(+)
> > >
> > > diff --git a/src/lxc/lxccontainer.c b/src/lxc/lxccontainer.c
> > > index 42e23e7..8edf6a2 100644
> > > --- a/src/lxc/lxccontainer.c
> > > +++ b/src/lxc/lxccontainer.c
> > > @@ -2894,6 +2894,99 @@ static int create_file_dirname(char *path,
struct lxc_conf *conf)
> > >       return ret;
> > >  }
> > >
> > > +/* When we clone a container with overlay or aufs lxc.mount.entry
entries we
> > > +*  need to update these absolute paths. In order to do this we add
the function
> > > +*  update_union_mount_entry_paths() in lxccontainer.c. The function
operates on
> > > +*  c->lxc_conf->unexpanded_config instead of the intuitively
plausible
> > > +*  c->lxc_conf->mount_list because the latter also contains mounts
from other
> > > +*  files as well as generic mounts. */
> > > +static int update_union_mount_entry_paths(struct lxc_conf *lxc_conf,
> > > +                                       const char *lxc_path,
> > > +                                       const char *lxc_name,
> > > +                                       const char *newpath,
> > > +                                       const char *newname)
> > > +{
> > > +     char new_upper[MAXPATHLEN];
> > > +     char new_work[MAXPATHLEN];
> > > +     char old_upper[MAXPATHLEN];
> > > +     char old_work[MAXPATHLEN];
> > > +     char *cleanpath = NULL;
> > > +     int i;
> > > +     int fret = -1;
> > > +     int ret = 0;
> > > +     struct lxc_list *iterator;
> > > +     const char *ovl_dirs[] = {"br", "upperdir", "workdir"};
> > > +
> > > +     cleanpath = strdup(newpath);
> > > +     if (!cleanpath)
> > > +             goto err;
> > > +
> > > +     remove_trailing_slashes(cleanpath);
> > > +
> >
> > Would be wortha comment here saying "we have to update the unexpanded
> > configuration separately from the expanded one."

I can insert it, add your Acked-by line to the cover letter and leave a
short reminder in the cover letter that I only inserted a comment per your
request so you know what's going on. Ok?

> >
> > > +     for (i = 0; i < sizeof(ovl_dirs) / sizeof(ovl_dirs[0]); i++) {
> > > +             if (!clone_update_unexp_ovl_dir(lxc_conf, lxc_path,
newpath,
> > > +                                             lxc_name, newname,
ovl_dirs[i]))
> > > +                     goto err;
> > > +     }
> > > +
> > > +     ret = snprintf(old_work, MAXPATHLEN, "workdir=%s/%s", lxc_path,
lxc_name);
> > > +     if (ret < 0 || ret >= MAXPATHLEN)
> > > +             goto err;
> > > +
> > > +     ret = snprintf(new_work, MAXPATHLEN, "workdir=%s/%s",
cleanpath, newname);
> > > +     if (ret < 0 || ret >= MAXPATHLEN)
> > > +             goto err;
> > > +
> > > +     lxc_list_for_each(iterator, &lxc_conf->mount_list) {
> > > +             char *mnt_entry = NULL;
> > > +             char *new_mnt_entry = NULL;
> > > +             char *tmp = NULL;
> > > +             char *tmp_mnt_entry = NULL;
> > > +             mnt_entry = iterator->elem;
> > > +
> > > +             if (strstr(mnt_entry, "overlay"))
> > > +                     tmp = "upperdir";
> > > +             else if (strstr(mnt_entry, "aufs"))
> > > +                     tmp = "br";
> > > +
> > > +             if (!tmp)
> > > +                     continue;
> > > +
> > > +                     ret = snprintf(old_upper, MAXPATHLEN,
"%s=%s/%s", tmp, lxc_path, lxc_name);
> > > +                     if (ret < 0 || ret >= MAXPATHLEN)
> > > +                             goto err;
> > > +
> > > +                     ret = snprintf(new_upper, MAXPATHLEN,
"%s=%s/%s", tmp, cleanpath, newname);
> > > +                     if (ret < 0 || ret >= MAXPATHLEN)
> > > +                             goto err;
> > > +
> > > +                     if (strstr(mnt_entry, old_upper)) {
> > > +                             tmp_mnt_entry =
lxc_string_replace(old_upper, new_upper, mnt_entry);
> > > +                     }
> > > +
> > > +                     if (strstr(mnt_entry, old_work)) {
> > > +                             if (tmp_mnt_entry)
> > > +                                     new_mnt_entry =
lxc_string_replace(old_work, new_work, tmp_mnt_entry);
> > > +                     }
> > > +
> > > +                     if (new_mnt_entry) {
> > > +                             free(iterator->elem);
> > > +                             iterator->elem = strdup(new_mnt_entry);
> > > +                     } else if (tmp_mnt_entry) {
> > > +                             free(iterator->elem);
> > > +                             iterator->elem = strdup(tmp_mnt_entry);
> > > +                     }
> > > +
> > > +                     free(new_mnt_entry);
> > > +                     free(tmp_mnt_entry);
> > > +     }
> > > +
> > > +     fret = 0;
> > > +err:
> > > +     free(cleanpath);
> > > +     return fret;
> > > +}
> > > +
> > >  static struct lxc_container *do_lxcapi_clone(struct lxc_container
*c, const char *newname,
> > >               const char *lxcpath, int flags,
> > >               const char *bdevtype, const char *bdevdata, uint64_t
newsize,
> > > @@ -3009,6 +3102,10 @@ static struct lxc_container
*do_lxcapi_clone(struct lxc_container *c, const char
> > >               }
> > >       }
> > >
> > > +     // update absolute paths for union mount directories
> > > +     if (update_union_mount_entry_paths(c2->lxc_conf,
c->config_path, c->name, lxcpath, newname) < 0)
> > > +             goto out;
> > > +
> > >       // We've now successfully created c2's storage, so clear it out
if we
> > >       // fail after this
> > >       storage_copied = 1;
> > > --
> > > 2.6.2
> > >
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.linuxcontainers.org/pipermail/lxc-devel/attachments/20151030/8db3c823/attachment.html>


More information about the lxc-devel mailing list