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    Subject[PATCH 3/3] user namespaces: reset task's credentials on CLONE_NEWUSER
    Currently, creating a new user namespace does not reset
    the task's uid or gid. Since generally that is done as
    root because it requires CAP_SYS_ADMIN, and since the
    first uid in the new namespace is 0, one usually doesn't
    notice. However, if one does

    capset cap_sys_admin=ep ns_exec
    su - hallyn
    ns_exec -U /bin/sh
    id

    then one will see hallyn's userid, and all preexisting
    groups.

    With this patch, cloning a new user namespace will set
    the task's uid and gid to 0, and reset the group_info to
    the empty set assigned to init.

    Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>

    ---

    kernel/user_namespace.c | 12 ++++++++++++
    1 files changed, 12 insertions(+), 0 deletions(-)

    4a159b503ed06f6d999b80680538a51ee39d6bd5
    diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
    index d59f193..3fbf520 100644
    --- a/kernel/user_namespace.c
    +++ b/kernel/user_namespace.c
    @@ -9,6 +9,7 @@
    #include <linux/nsproxy.h>
    #include <linux/slab.h>
    #include <linux/user_namespace.h>
    +#include <linux/init_task.h>

    /*
    * Clone a new ns copying an original user ns, setting refcount to 1
    @@ -47,6 +48,17 @@ int create_new_userns(int flags, struct
    put_user_ns(ns);

    task_switch_uid(tsk, ns->root_user);
    + tsk->uid = tsk->euid = tsk->suid = tsk->fsuid = 0;
    + tsk->gid = tsk->egid = tsk->sgid = tsk->fsgid = 0;
    +
    + /* this can't be safe for unshare, can it? it's safe
    + * for fork, though. I'm tempted to limit clone_newuser to
    + * fork only */
    + task_lock(tsk);
    + put_group_info(tsk->group_info);
    + tsk->group_info = &init_groups;
    + get_group_info(tsk->group_info);
    + task_unlock(tsk);

    return 0;
    }
    --
    1.1.6

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