On 02.05.2017 13:03, Kirill Tkhai wrote:
>
>
> On 29.04.2017 22:25, Eric W. Biederman wrote:
>>
>> It is pointless and confusing to allow a pid namespace hierarchy and
>> the user namespace hierarchy to get out of sync. The owner of a child
>> pid namespace should be the owner of the parent pid namespace or
>> a descendant of the owner of the parent pid namespace.
>>
>> Otherwise it is possible to construct scenarios where it is legal to
>> do something in a parent pid namespace but in a child pid namespace.
>>
>> It requires use of setns into a pid namespace (but not into a user
>> namespace) to create such a scenario.
>>
>> Add the function in_userns to help in making this determination.
>>
>> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
>> ---
>>
>> While review a patch from Kiril Tkhai I realized we were missing this
>> sanity check....
>>
>> include/linux/user_namespace.h | 8 +++++++-
>> kernel/pid_namespace.c | 4 ++++
>> kernel/user_namespace.c | 18 ++++++++++++------
>> 3 files changed, 23 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
>> index 32354b4b4b2b..497ed50004db 100644
>> --- a/include/linux/user_namespace.h
>> +++ b/include/linux/user_namespace.h
>> @@ -112,8 +112,9 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t,
>> extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *);
>> extern int proc_setgroups_show(struct seq_file *m, void *v);
>> extern bool userns_may_setgroups(const struct user_namespace *ns);
>> +extern bool in_userns(const struct user_namespace *ancestor,
>> + const struct user_namespace *child);
>> extern bool current_in_userns(const struct user_namespace *target_ns);
>> -
>> struct ns_common *ns_get_owner(struct ns_common *ns);
>> #else
>>
>> @@ -144,6 +145,11 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns)
>> return true;
>> }
>>
>> +static inline bool in_userns(const struct user_namespace *target_ns)
>> +{
>> + return true;
>> +}
>> +
>> static inline bool current_in_userns(const struct user_namespace *target_ns)
>> {
>> return true;
>> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
>> index de461aa0bf9a..749147f5a613 100644
>> --- a/kernel/pid_namespace.c
>> +++ b/kernel/pid_namespace.c
>> @@ -101,6 +101,10 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
>> int i;
>> int err;
>>
>> + err = -EINVAL;
>> + if (!in_userns(parent_pid_ns->user_ns, user_ns))
>> + goto out;
>> +
>> err = -ENOSPC;
>> if (level > MAX_PID_NS_LEVEL)
>> goto out;
>> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
>> index 2f735cbe05e8..7d8658fbabc8 100644
>> --- a/kernel/user_namespace.c
>> +++ b/kernel/user_namespace.c
>> @@ -986,19 +986,25 @@ bool userns_may_setgroups(const struct user_namespace *ns)
>> }
>>
>> /*
>> - * Returns true if @ns is the same namespace as or a descendant of
>> - * @target_ns.
>> + * Returns true if @child is the same namespace or a descendant of
>> + * @ancestor.
>> */
>> -bool current_in_userns(const struct user_namespace *target_ns)
>> +bool in_userns(const struct user_namespace *ancestor,
>> + const struct user_namespace *child)
>> {
>> - struct user_namespace *ns;
>> - for (ns = current_user_ns(); ns; ns = ns->parent) {
>> - if (ns == target_ns)
>> + const struct user_namespace *ns;
>> + for (ns = child; ns; ns = ns->parent) {
>> + if (ns == ancestor)
>> return true;
>> }
>> return false;
>> }
>
> We have user_namespace::level, so it's possible to stop iterations earlier
> and save some cpu cycles:
>
> for (ns = child; ns->level >= ancestor->level; ns = ns->parent)
Just ">" here.
> ;
> return (ns == ancestor);
>
>>
>> +bool current_in_userns(const struct user_namespace *target_ns)
>> +{
>> + return in_userns(target_ns, current_user_ns());
>> +}
>> +
>> static inline struct user_namespace *to_user_ns(struct ns_common *ns)
>> {
>> return container_of(ns, struct user_namespace, ns);
>>
