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Message-Id: <20160721164014.17534-3-ebiederm@xmission.com>
Date: Thu, 21 Jul 2016 11:40:07 -0500
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: Linux Containers <containers@...ts.linux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>, Jann Horn <jann@...jh.net>,
Kees Cook <keescook@...omium.org>,
Nikolay Borisov <kernel@...p.com>,
"Serge E. Hallyn" <serge@...lyn.com>,
Seth Forshee <seth.forshee@...onical.com>,
linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH v2 03/10] userns: Add a limit on the number of user namespaces
Export the export the maximum number of user namespaces as
/proc/sys/userns/max_user_namespaces.
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
include/linux/user_namespace.h | 2 ++
kernel/fork.c | 2 ++
kernel/user_namespace.c | 69 +++++++++++++++++++++++++++++++++++++-----
3 files changed, 65 insertions(+), 8 deletions(-)
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 7d59af1f08f1..ba6a995178f9 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -43,6 +43,8 @@ struct user_namespace {
struct ctl_table_set set;
struct ctl_table_header *sysctls;
#endif
+ int max_user_namespaces;
+ atomic_t user_namespaces;
};
extern struct user_namespace init_user_ns;
diff --git a/kernel/fork.c b/kernel/fork.c
index 5c2c355aa97f..95d5498c463f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -323,6 +323,8 @@ void __init fork_init(void)
init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
init_task.signal->rlim[RLIMIT_SIGPENDING] =
init_task.signal->rlim[RLIMIT_NPROC];
+
+ init_user_ns.max_user_namespaces = max_threads;
}
int __weak arch_dup_task_struct(struct task_struct *dst,
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 10afbb55dfc2..0061550e3282 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -29,6 +29,7 @@ static DEFINE_MUTEX(userns_state_mutex);
static bool new_idmap_permitted(const struct file *file,
struct user_namespace *ns, int cap_setid,
struct uid_gid_map *map);
+#define COUNT_MAX (INT_MAX - 1)
#ifdef CONFIG_SYSCTL
static struct ctl_table_set *
@@ -63,7 +64,18 @@ static struct ctl_table_root set_root = {
.permissions = set_permissions,
};
+static int zero = 0;
+static int count_max = COUNT_MAX;
static struct ctl_table userns_table[] = {
+ {
+ .procname = "max_user_namespaces",
+ .data = &init_user_ns.max_user_namespaces,
+ .maxlen = sizeof(init_user_ns.max_user_namespaces),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &count_max,
+ },
{ }
};
#endif /* CONFIG_SYSCTL */
@@ -75,6 +87,8 @@ static bool setup_userns_sysctls(struct user_namespace *ns)
setup_sysctl_set(&ns->set, &set_root, set_is_seen);
tbl = kmemdup(userns_table, sizeof(userns_table), GFP_KERNEL);
if (tbl) {
+ tbl[0].data = &ns->max_user_namespaces;
+
ns->sysctls = __register_sysctl_table(&ns->set, "userns", tbl);
}
if (!ns->sysctls) {
@@ -113,6 +127,34 @@ static void set_cred_user_ns(struct cred *cred, struct user_namespace *user_ns)
cred->user_ns = user_ns;
}
+static bool inc_user_namespaces(struct user_namespace *ns)
+{
+ struct user_namespace *pos, *bad;
+ for (pos = ns; pos; pos = pos->parent) {
+ int max = READ_ONCE(pos->max_user_namespaces);
+ int sum = atomic_inc_return(&pos->user_namespaces);
+ if (sum > max)
+ goto fail;
+ }
+ return true;
+fail:
+ bad = pos;
+ atomic_dec(&pos->user_namespaces);
+ for (pos = ns; pos != bad; pos = pos->parent)
+ atomic_dec(&pos->user_namespaces);
+
+ return false;
+}
+
+static void dec_user_namespaces(struct user_namespace *ns)
+{
+ struct user_namespace *pos;
+ for (pos = ns; pos; pos = pos->parent) {
+ int dec = atomic_dec_if_positive(&pos->user_namespaces);
+ WARN_ON_ONCE(dec < 0);
+ }
+}
+
/*
* Create a new user namespace, deriving the creator from the user in the
* passed credentials, and replacing that user with the new root user for the
@@ -128,8 +170,12 @@ int create_user_ns(struct cred *new)
kgid_t group = new->egid;
int ret;
+ ret = -EUSERS;
if (parent_ns->level > 32)
- return -EUSERS;
+ goto fail;
+
+ if (!inc_user_namespaces(parent_ns))
+ goto fail;
/*
* Verify that we can not violate the policy of which files
@@ -137,26 +183,27 @@ int create_user_ns(struct cred *new)
* by verifing that the root directory is at the root of the
* mount namespace which allows all files to be accessed.
*/
+ ret = -EPERM;
if (current_chrooted())
- return -EPERM;
+ goto fail_dec;
/* The creator needs a mapping in the parent user namespace
* or else we won't be able to reasonably tell userspace who
* created a user_namespace.
*/
+ ret = -EPERM;
if (!kuid_has_mapping(parent_ns, owner) ||
!kgid_has_mapping(parent_ns, group))
- return -EPERM;
+ goto fail_dec;
+ ret = -ENOMEM;
ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL);
if (!ns)
- return -ENOMEM;
+ goto fail_dec;
ret = ns_alloc_inum(&ns->ns);
- if (ret) {
- kmem_cache_free(user_ns_cachep, ns);
- return ret;
- }
+ if (ret)
+ goto fail_free;
ns->ns.ops = &userns_operations;
atomic_set(&ns->count, 1);
@@ -165,6 +212,7 @@ int create_user_ns(struct cred *new)
ns->level = parent_ns->level + 1;
ns->owner = owner;
ns->group = group;
+ ns->max_user_namespaces = COUNT_MAX;
/* Inherit USERNS_SETGROUPS_ALLOWED from our parent */
mutex_lock(&userns_state_mutex);
@@ -185,7 +233,11 @@ fail_keyring:
key_put(ns->persistent_keyring_register);
#endif
ns_free_inum(&ns->ns);
+fail_free:
kmem_cache_free(user_ns_cachep, ns);
+fail_dec:
+ dec_user_namespaces(parent_ns);
+fail:
return ret;
}
@@ -221,6 +273,7 @@ void free_user_ns(struct user_namespace *ns)
#endif
ns_free_inum(&ns->ns);
kmem_cache_free(user_ns_cachep, ns);
+ dec_user_namespaces(parent);
ns = parent;
} while (atomic_dec_and_test(&parent->count));
}
--
2.8.3
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