[lxc-devel] [PATCH] mount_proc_if_needed: only safe mount when rootfs is defined

[Serge Hallyn]

Quoting Bogdan Purcareata (bogdan.purcareata at nxp.com):
> The safe_mount function was introduced in order to address CVE-2015-1335,
> one of the vulnerabilities being a mount with a symlink for the
> destination path. In scenarios such as lxc-execute with no rootfs, the
> destination path is the host /proc, which is previously mounted by the
> host, and is unmounted and mounted again in a new set of namespaces,
> therefore eliminating the need to check for it being a symlink.
> 
> Mount the rootfs normally if the rootfs is NULL, keep the safe mount
> only for scenarios where a different rootfs is defined.
> 
> Signed-off-by: Bogdan Purcareata <bogdan.purcareata at nxp.com>

Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>

> ---
>  src/lxc/conf.c  |  1 +
>  src/lxc/utils.c | 10 +++++++++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/src/lxc/conf.c b/src/lxc/conf.c
> index 632dde3..1e30c0c 100644
> --- a/src/lxc/conf.c
> +++ b/src/lxc/conf.c
> @@ -3509,6 +3509,7 @@ int ttys_shift_ids(struct lxc_conf *c)
>  	return 0;
>  }
>  
> +/* NOTE: not to be called from inside the container namespace! */
>  int tmp_proc_mount(struct lxc_conf *lxc_conf)
>  {
>  	int mounted;
> diff --git a/src/lxc/utils.c b/src/lxc/utils.c
> index ed8c4c4..e31228d 100644
> --- a/src/lxc/utils.c
> +++ b/src/lxc/utils.c
> @@ -1704,6 +1704,8 @@ int safe_mount(const char *src, const char *dest, const char *fstype,
>   *
>   * Returns < 0 on failure, 0 if the correct proc was already mounted
>   * and 1 if a new proc was mounted.
> + *
> + * NOTE: not to be called from inside the container namespace!
>   */
>  int mount_proc_if_needed(const char *rootfs)
>  {
> @@ -1737,8 +1739,14 @@ int mount_proc_if_needed(const char *rootfs)
>  	return 0;
>  
>  domount:
> -	if (safe_mount("proc", path, "proc", 0, NULL, rootfs) < 0)
> +	if (!strcmp(rootfs,"")) /* rootfs is NULL */
> +		ret = mount("proc", path, "proc", 0, NULL);
> +	else
> +		ret = safe_mount("proc", path, "proc", 0, NULL, rootfs);
> +
> +	if (ret < 0)
>  		return -1;
> +
>  	INFO("Mounted /proc in container for security transition");
>  	return 1;
>  }
> -- 
> 1.9.1
> 
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