diff options
| author | Eric W. Biederman <ebiederm@xmission.com> | 2014-12-05 18:01:11 -0600 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-01-08 09:58:16 -0800 |
| commit | fc9b65e3d7703e6d63875b0b233bbe26a4a513ba (patch) | |
| tree | 7686f17848a927d80398803eab339cb9084343ed | |
| parent | b8a0441b542f6d6bd6fda46cc735ae71392cb845 (diff) | |
userns: Don't allow setgroups until a gid mapping has been setablished
commit 273d2c67c3e179adb1e74f403d1e9a06e3f841b5 upstream.
setgroups is unique in not needing a valid mapping before it can be called,
in the case of setgroups(0, NULL) which drops all supplemental groups.
The design of the user namespace assumes that CAP_SETGID can not actually
be used until a gid mapping is established. Therefore add a helper function
to see if the user namespace gid mapping has been established and call
that function in the setgroups permission check.
This is part of the fix for CVE-2014-8989, being able to drop groups
without privilege using user namespaces.
Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | include/linux/user_namespace.h | 5 | ||||
| -rw-r--r-- | kernel/groups.c | 4 | ||||
| -rw-r--r-- | kernel/user_namespace.c | 14 |
3 files changed, 22 insertions, 1 deletions
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index 14105c26a836..648cf88c5d6d 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -59,6 +59,7 @@ extern struct seq_operations proc_projid_seq_operations; extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *); extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *); extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *); +extern bool userns_may_setgroups(const struct user_namespace *ns); #else static inline struct user_namespace *get_user_ns(struct user_namespace *ns) @@ -83,6 +84,10 @@ static inline void put_user_ns(struct user_namespace *ns) { } +static inline bool userns_may_setgroups(const struct user_namespace *ns) +{ + return true; +} #endif void update_mnt_policy(struct user_namespace *userns); diff --git a/kernel/groups.c b/kernel/groups.c index 984bb629c68c..67b4ba30475f 100644 --- a/kernel/groups.c +++ b/kernel/groups.c @@ -6,6 +6,7 @@ #include <linux/slab.h> #include <linux/security.h> #include <linux/syscalls.h> +#include <linux/user_namespace.h> #include <asm/uaccess.h> /* init to 2 - one for init_task, one to ensure it is never freed */ @@ -227,7 +228,8 @@ bool may_setgroups(void) { struct user_namespace *user_ns = current_user_ns(); - return ns_capable(user_ns, CAP_SETGID); + return ns_capable(user_ns, CAP_SETGID) && + userns_may_setgroups(user_ns); } /* diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 59790206ca2e..b083fa233daa 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -832,6 +832,20 @@ static bool new_idmap_permitted(const struct file *file, return false; } +bool userns_may_setgroups(const struct user_namespace *ns) +{ + bool allowed; + + mutex_lock(&id_map_mutex); + /* It is not safe to use setgroups until a gid mapping in + * the user namespace has been established. + */ + allowed = ns->gid_map.nr_extents != 0; + mutex_unlock(&id_map_mutex); + + return allowed; +} + static void *userns_get(struct task_struct *task) { struct user_namespace *user_ns; |