[lxc-devel] [PATCH v3] Parse rootfs->path

[Serge Hallyn]

Quoting Christian Brauner (christianvanbrauner at gmail.com):
> The mount_entry_overlay_dirs() and mount_entry_aufs_dirs() functions create
> workdirs and upperdirs for overlay and aufs lxc.mount.entry entries. They try
> to make sure that the workdirs and upperdirs can only be created under the
> containerdir (e.g. /path/to/the/container/CONTAINERNAME). In order to do this
> the right hand side of
> 
>                 if ((strncmp(upperdir, lxcpath, dirlen) == 0) && (strncmp(upperdir, rootfs->path, rootfslen) != 0))
> 
> was thought to check if the rootfs->path is not present in the workdir and
> upperdir mount options. But the current check is bogus since it will be
> trivially true whenever the container is a block-dev or overlay or aufs backed
> since the rootfs->path will then have a form like e.g.
> 
>         overlayfs:/some/path:/some/other/path
> 
> This patch adds the function ovl_get_rootfs_dir() which parses rootfs->path by
> searching backwards for the first occurrence of the delimiter pair ":/". We do
> not simply search for ":" since it might be used in path names. If ":/" is not
> found we assume the container is directory backed and simply return
> strdup(rootfs->path).
> 
> Signed-off-by: Christian Brauner <christianvanbrauner at gmail.com>
> ---
>  src/lxc/conf.c | 115 ++++++++++++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 90 insertions(+), 25 deletions(-)
> 
> diff --git a/src/lxc/conf.c b/src/lxc/conf.c
> index 16a62f8..301fe50 100644
> --- a/src/lxc/conf.c
> +++ b/src/lxc/conf.c
> @@ -1815,12 +1815,65 @@ static void cull_mntent_opt(struct mntent *mntent)
>  	}
>  }
>  
> +static char *ovl_get_rootfs_dir(const char *rootfs_path, size_t *rootfslen)
> +{
> +	char *end = NULL;
> +	char *s1 = NULL;
> +	char *s2 = NULL;
> +	char *rootfsdir = NULL;
> +	char *tmp = NULL;
> +	size_t len = 0;
> +	size_t slen = 0;
> +
> +	if (!rootfs_path || !rootfslen )
> +		return NULL;
> +
> +	*rootfslen = 0;
> +
> +	s1 = strdup(rootfs_path);
> +	if (!s1)
> +		return NULL;
> +
> +	s2 = malloc(strlen(rootfs_path) + 1);
> +	if (!s2) {
> +		free(s1);
> +		return NULL;
> +	}
> +	end = stpcpy(s2, rootfs_path);
> +
> +	/* If we find :/ in rootfs_path it means we either have a block-dev or
> +	 * overlay or aufs container. */
> +	while ((tmp = strrchr(s1, ':'))) {
> +		len = strlen(tmp);
> +		*rootfslen += len;

If it is "overlay:/some/rootfs:/some/delta0", you will find the
delta0 and return it as rootfsdir?

(or am i misreading?)

> +		if (strncmp(tmp, ":/", 2) == 0) {
> +			rootfsdir = strdup(end - *rootfslen + 1);
> +			break;
> +		} else {
> +			slen = strlen(s1);
> +			s1[slen - len] = '\0';
> +		}
> +	}
> +	free(s1);
> +
> +	if (!*rootfslen && !tmp)
> +		rootfsdir = s2;
> +	else
> +		free(s2);
> +
> +	if (rootfsdir)
> +		*rootfslen = strlen(rootfsdir);
> +
> +	return rootfsdir;
> +}