On Thu, Dec 8, 2016 at 9:14 AM, Stephen Smalley <sds@xxxxxxxxxxxxx> wrote:
> commit aad82892af261b9903cc11c55be3ecf5f0b0b4f8 ("selinux: Add support for
> unprivileged mounts from user namespaces") prohibited any use of context
> mount options within non-init user namespaces. However, this breaks
> use of context mount options for tmpfs mounts within user namespaces,
> which are being used by Docker/runc. There is no reason to block such
> usage for tmpfs, ramfs or devpts. Exempt these filesystem types
> from this restriction.
>
> Before:
> sh$ userns_child_exec -p -m -U -M '0 1000 1' -G '0 1000 1' bash
> sh# mount -t tmpfs -o context=system_u:object_r:user_tmp_t:s0:c13 none /tmp
> mount: tmpfs is write-protected, mounting read-only
> mount: cannot mount tmpfs read-only
>
> After:
> sh$ userns_child_exec -p -m -U -M '0 1000 1' -G '0 1000 1' bash
> sh# mount -t tmpfs -o context=system_u:object_r:user_tmp_t:s0:c13 none /tmp
> sh# ls -Zd /tmp
> unconfined_u:object_r:user_tmp_t:s0:c13 /tmp
>
> Signed-off-by: Stephen Smalley <sds@xxxxxxxxxxxxx>
> ---
> security/selinux/hooks.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
Merged, thanks.
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 8a90a0b..8fae174 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -834,10 +834,14 @@ static int selinux_set_mnt_opts(struct super_block *sb,
> }
>
> /*
> - * If this is a user namespace mount, no contexts are allowed
> - * on the command line and security labels must be ignored.
> + * If this is a user namespace mount and the filesystem type is not
> + * explicitly whitelisted, then no contexts are allowed on the command
> + * line and security labels must be ignored.
> */
> - if (sb->s_user_ns != &init_user_ns) {
> + if (sb->s_user_ns != &init_user_ns &&
> + strcmp(sb->s_type->name, "tmpfs") &&
> + strcmp(sb->s_type->name, "ramfs") &&
> + strcmp(sb->s_type->name, "devpts")) {
> if (context_sid || fscontext_sid || rootcontext_sid ||
> defcontext_sid) {
> rc = -EACCES;
> --
> 2.7.4
>
--
paul moore
www.paul-moore.com
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