On Mon, Dec 8, 2014 at 2:10 PM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
>
> If you did not create the user namespace and are allowed
> to write to uid_map or gid_map you should already have the necessary
> privilege in the parent user namespace to establish any mapping
> you want so this will not affect userspace in practice.
>
> Limiting unprivileged uid mapping establishment to the creator of the
> user namespace reduces the set of credentials that must be verified
> can be obtained without privielge, making code verification simpler.
>
s/privielge/privilege/
But I still can't parse that sentence.
The code itself is:
Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Limiting unprivileged gid mapping establishment (which is temporarily
> absent) to the creator of the user namespace also ensures that the
> combination of uid and gid can already be obtained without privilege.
>
> This is part of the fix for CVE-2014-8989.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
> ---
> kernel/user_namespace.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> index da1eeb927b21..413f60fd5983 100644
> --- a/kernel/user_namespace.c
> +++ b/kernel/user_namespace.c
> @@ -812,14 +812,16 @@ static bool new_idmap_permitted(const struct file *file,
> struct user_namespace *ns, int cap_setid,
> struct uid_gid_map *new_map)
> {
> + const struct cred *cred = file->f_cred;
> /* Don't allow mappings that would allow anything that wouldn't
> * be allowed without the establishment of unprivileged mappings.
> */
> - if ((new_map->nr_extents == 1) && (new_map->extent[0].count == 1)) {
> + if ((new_map->nr_extents == 1) && (new_map->extent[0].count == 1) &&
> + uid_eq(ns->owner, cred->euid)) {
> u32 id = new_map->extent[0].lower_first;
> if (cap_setid == CAP_SETUID) {
> kuid_t uid = make_kuid(ns->parent, id);
> - if (uid_eq(uid, file->f_cred->euid))
> + if (uid_eq(uid, cred->euid))
> return true;
> }
> }
> --
> 1.9.1
>
--
Andy Lutomirski
AMA Capital Management, LLC
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