[lxc-devel] [PATCH] mount_proc_if_needed: only safe mount when rootfs is defined
Serge Hallyn
serge.hallyn at ubuntu.com
Sat Jan 23 06:35:20 UTC 2016
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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