2 * This program is free software; you can redistribute it and/or
3 * modify it under the terms of the GNU General Public License as
4 * published by the Free Software Foundation, version 2 of the
8 #include <linux/stat.h>
9 #include <linux/sysctl.h>
10 #include <linux/slab.h>
11 #include <linux/hash.h>
12 #include <linux/user_namespace.h>
14 #define UCOUNTS_HASHTABLE_BITS 10
15 static struct hlist_head ucounts_hashtable
[(1 << UCOUNTS_HASHTABLE_BITS
)];
16 static DEFINE_SPINLOCK(ucounts_lock
);
18 #define ucounts_hashfn(ns, uid) \
19 hash_long((unsigned long)__kuid_val(uid) + (unsigned long)(ns), \
20 UCOUNTS_HASHTABLE_BITS)
21 #define ucounts_hashentry(ns, uid) \
22 (ucounts_hashtable + ucounts_hashfn(ns, uid))
26 static struct ctl_table_set
*
27 set_lookup(struct ctl_table_root
*root
)
29 return ¤t_user_ns()->set
;
32 static int set_is_seen(struct ctl_table_set
*set
)
34 return ¤t_user_ns()->set
== set
;
37 static int set_permissions(struct ctl_table_header
*head
,
38 struct ctl_table
*table
)
40 struct user_namespace
*user_ns
=
41 container_of(head
->set
, struct user_namespace
, set
);
44 /* Allow users with CAP_SYS_RESOURCE unrestrained access */
45 if (ns_capable(user_ns
, CAP_SYS_RESOURCE
))
46 mode
= (table
->mode
& S_IRWXU
) >> 6;
48 /* Allow all others at most read-only access */
49 mode
= table
->mode
& S_IROTH
;
50 return (mode
<< 6) | (mode
<< 3) | mode
;
53 static struct ctl_table_root set_root
= {
55 .permissions
= set_permissions
,
59 static int int_max
= INT_MAX
;
60 static struct ctl_table user_table
[] = {
62 .procname
= "max_user_namespaces",
63 .data
= &init_user_ns
.max_user_namespaces
,
64 .maxlen
= sizeof(init_user_ns
.max_user_namespaces
),
66 .proc_handler
= proc_dointvec_minmax
,
72 #endif /* CONFIG_SYSCTL */
74 bool setup_userns_sysctls(struct user_namespace
*ns
)
77 struct ctl_table
*tbl
;
78 setup_sysctl_set(&ns
->set
, &set_root
, set_is_seen
);
79 tbl
= kmemdup(user_table
, sizeof(user_table
), GFP_KERNEL
);
81 tbl
[0].data
= &ns
->max_user_namespaces
;
83 ns
->sysctls
= __register_sysctl_table(&ns
->set
, "user", tbl
);
87 retire_sysctl_set(&ns
->set
);
94 void retire_userns_sysctls(struct user_namespace
*ns
)
97 struct ctl_table
*tbl
;
99 tbl
= ns
->sysctls
->ctl_table_arg
;
100 unregister_sysctl_table(ns
->sysctls
);
101 retire_sysctl_set(&ns
->set
);
106 static struct ucounts
*find_ucounts(struct user_namespace
*ns
, kuid_t uid
, struct hlist_head
*hashent
)
108 struct ucounts
*ucounts
;
110 hlist_for_each_entry(ucounts
, hashent
, node
) {
111 if (uid_eq(ucounts
->uid
, uid
) && (ucounts
->ns
== ns
))
117 static struct ucounts
*get_ucounts(struct user_namespace
*ns
, kuid_t uid
)
119 struct hlist_head
*hashent
= ucounts_hashentry(ns
, uid
);
120 struct ucounts
*ucounts
, *new;
122 spin_lock(&ucounts_lock
);
123 ucounts
= find_ucounts(ns
, uid
, hashent
);
125 spin_unlock(&ucounts_lock
);
127 new = kzalloc(sizeof(*new), GFP_KERNEL
);
133 atomic_set(&new->count
, 0);
135 spin_lock(&ucounts_lock
);
136 ucounts
= find_ucounts(ns
, uid
, hashent
);
140 hlist_add_head(&new->node
, hashent
);
144 if (!atomic_add_unless(&ucounts
->count
, 1, INT_MAX
))
146 spin_unlock(&ucounts_lock
);
150 static void put_ucounts(struct ucounts
*ucounts
)
152 if (atomic_dec_and_test(&ucounts
->count
)) {
153 spin_lock(&ucounts_lock
);
154 hlist_del_init(&ucounts
->node
);
155 spin_unlock(&ucounts_lock
);
161 static inline bool atomic_inc_below(atomic_t
*v
, int u
)
166 if (unlikely(c
>= u
))
168 old
= atomic_cmpxchg(v
, c
, c
+1);
169 if (likely(old
== c
))
175 struct ucounts
*inc_user_namespaces(struct user_namespace
*ns
, kuid_t uid
)
177 struct ucounts
*ucounts
, *iter
, *bad
;
178 struct user_namespace
*tns
;
179 ucounts
= get_ucounts(ns
, uid
);
180 for (iter
= ucounts
; iter
; iter
= tns
->ucounts
) {
183 max
= READ_ONCE(tns
->max_user_namespaces
);
184 if (!atomic_inc_below(&iter
->user_namespaces
, max
))
190 for (iter
= ucounts
; iter
!= bad
; iter
= iter
->ns
->ucounts
)
191 atomic_dec(&iter
->user_namespaces
);
193 put_ucounts(ucounts
);
197 void dec_user_namespaces(struct ucounts
*ucounts
)
199 struct ucounts
*iter
;
200 for (iter
= ucounts
; iter
; iter
= iter
->ns
->ucounts
) {
201 int dec
= atomic_dec_if_positive(&iter
->user_namespaces
);
202 WARN_ON_ONCE(dec
< 0);
204 put_ucounts(ucounts
);
208 static __init
int user_namespace_sysctl_init(void)
211 static struct ctl_table_header
*user_header
;
212 static struct ctl_table empty
[1];
214 * It is necessary to register the user directory in the
215 * default set so that registrations in the child sets work
218 user_header
= register_sysctl("user", empty
);
219 BUG_ON(!user_header
);
220 BUG_ON(!setup_userns_sysctls(&init_user_ns
));
224 subsys_initcall(user_namespace_sysctl_init
);