On Fri, Nov 10, 2017 at 2:25 AM, Serge E. Hallyn <serge@xxxxxxxxxx> wrote: > Quoting Mahesh Bandewar (mahesh@xxxxxxxxxxxx): >> From: Mahesh Bandewar <maheshb@xxxxxxxxxx> >> >> With this new notion of "controlled" user-namespaces, the controlled >> user-namespaces are marked at the time of their creation while the >> capabilities of processes that belong to them are controlled using the >> global mask. >> >> Init-user-ns is always uncontrolled and a process that has SYS_ADMIN >> that belongs to uncontrolled user-ns can create another (child) user- >> namespace that is uncontrolled. Any other process (that either does >> not have SYS_ADMIN or belongs to a controlled user-ns) can only >> create a user-ns that is controlled. >> >> global-capability-whitelist (controlled_userns_caps_whitelist) is used >> at the capability check-time and keeps the semantics for the processes >> that belong to uncontrolled user-ns as it is. Processes that belong to >> controlled user-ns however are subjected to different checks- >> >> (a) if the capability in question is controlled and process belongs >> to controlled user-ns, then it's always denied. >> (b) if the capability in question is NOT controlled then fall back >> to the traditional check. >> >> Signed-off-by: Mahesh Bandewar <maheshb@xxxxxxxxxx> >> --- >> include/linux/capability.h | 1 + >> include/linux/user_namespace.h | 20 ++++++++++++++++++++ >> kernel/capability.c | 5 +++++ >> kernel/user_namespace.c | 3 +++ >> security/commoncap.c | 8 ++++++++ >> 5 files changed, 37 insertions(+) >> >> diff --git a/include/linux/capability.h b/include/linux/capability.h >> index 6c0b9677c03f..b8c6cac18658 100644 >> --- a/include/linux/capability.h >> +++ b/include/linux/capability.h >> @@ -250,6 +250,7 @@ extern bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns); >> extern int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps); >> int proc_douserns_caps_whitelist(struct ctl_table *table, int write, >> void __user *buff, size_t *lenp, loff_t *ppos); >> +bool is_capability_controlled(int cap); >> >> extern int cap_convert_nscap(struct dentry *dentry, void **ivalue, size_t size); >> >> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h >> index c18e01252346..e890fe81b47e 100644 >> --- a/include/linux/user_namespace.h >> +++ b/include/linux/user_namespace.h >> @@ -22,6 +22,7 @@ struct uid_gid_map { /* 64 bytes -- 1 cache line */ >> }; >> >> #define USERNS_SETGROUPS_ALLOWED 1UL >> +#define USERNS_CONTROLLED 2UL >> >> #define USERNS_INIT_FLAGS USERNS_SETGROUPS_ALLOWED >> >> @@ -102,6 +103,16 @@ static inline void put_user_ns(struct user_namespace *ns) >> __put_user_ns(ns); >> } >> >> +static inline bool is_user_ns_controlled(const struct user_namespace *ns) >> +{ >> + return ns->flags & USERNS_CONTROLLED; >> +} >> + >> +static inline void mark_user_ns_controlled(struct user_namespace *ns) >> +{ >> + ns->flags |= USERNS_CONTROLLED; >> +} >> + >> struct seq_operations; >> extern const struct seq_operations proc_uid_seq_operations; >> extern const struct seq_operations proc_gid_seq_operations; >> @@ -160,6 +171,15 @@ static inline struct ns_common *ns_get_owner(struct ns_common *ns) >> { >> return ERR_PTR(-EPERM); >> } >> + >> +static inline bool is_user_ns_controlled(const struct user_namespace *ns) >> +{ >> + return false; >> +} >> + >> +static inline void mark_user_ns_controlled(struct user_namespace *ns) >> +{ >> +} >> #endif >> >> #endif /* _LINUX_USER_H */ >> diff --git a/kernel/capability.c b/kernel/capability.c >> index 62dbe3350c1b..40a38cc4ff43 100644 >> --- a/kernel/capability.c >> +++ b/kernel/capability.c >> @@ -510,6 +510,11 @@ bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns) >> } >> >> /* Controlled-userns capabilities routines */ >> +bool is_capability_controlled(int cap) >> +{ >> + return !cap_raised(controlled_userns_caps_whitelist, cap); >> +} >> + >> #ifdef CONFIG_SYSCTL >> int proc_douserns_caps_whitelist(struct ctl_table *table, int write, >> void __user *buff, size_t *lenp, loff_t *ppos) >> diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c >> index c490f1e4313b..f393ea5108f0 100644 >> --- a/kernel/user_namespace.c >> +++ b/kernel/user_namespace.c >> @@ -53,6 +53,9 @@ static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns) >> cred->cap_effective = CAP_FULL_SET; >> cred->cap_ambient = CAP_EMPTY_SET; >> cred->cap_bset = CAP_FULL_SET; >> + if (!ns_capable(user_ns->parent, CAP_SYS_ADMIN) || >> + is_user_ns_controlled(user_ns->parent)) >> + mark_user_ns_controlled(user_ns); > > Hm, why do this here, rather than at create_user_ns()? It > shouldn't be recalculated when someone does setns() should it? > You are absolutely right! It doesn't make sense to recalculate for every setns() call. It's a side effect of couple of iterations / approaches that I tried before finalizing this one. I'll move this block to create_user_ns() after the set_cred_user_ns() call so that this wont be triggered in setns() path. Thanks, --mahesh.. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html