1 // SPDX-License-Identifier: GPL-2.0
2 /* Copyright (c) 2022 Christian Brauner <brauner@kernel.org> */
4 #include <linux/cred.h>
6 #include <linux/mnt_idmapping.h>
7 #include <linux/slab.h>
8 #include <linux/user_namespace.h>
13 * Outside of this file vfs{g,u}id_t are always created from k{g,u}id_t,
14 * never from raw values. These are just internal helpers.
16 #define VFSUIDT_INIT_RAW(val) (vfsuid_t){ val }
17 #define VFSGIDT_INIT_RAW(val) (vfsgid_t){ val }
20 struct uid_gid_map uid_map
;
21 struct uid_gid_map gid_map
;
26 * Carries the initial idmapping of 0:0:4294967295 which is an identity
27 * mapping. This means that {g,u}id 0 is mapped to {g,u}id 0, {g,u}id 1 is
28 * mapped to {g,u}id 1, [...], {g,u}id 1000 to {g,u}id 1000, [...].
30 struct mnt_idmap nop_mnt_idmap
= {
31 .count
= REFCOUNT_INIT(1),
33 EXPORT_SYMBOL_GPL(nop_mnt_idmap
);
36 * initial_idmapping - check whether this is the initial mapping
37 * @ns: idmapping to check
39 * Check whether this is the initial mapping, mapping 0 to 0, 1 to 1,
40 * [...], 1000 to 1000 [...].
42 * Return: true if this is the initial mapping, false if not.
44 static inline bool initial_idmapping(const struct user_namespace
*ns
)
46 return ns
== &init_user_ns
;
50 * make_vfsuid - map a filesystem kuid according to an idmapping
51 * @idmap: the mount's idmapping
52 * @fs_userns: the filesystem's idmapping
53 * @kuid : kuid to be mapped
55 * Take a @kuid and remap it from @fs_userns into @idmap. Use this
56 * function when preparing a @kuid to be reported to userspace.
58 * If initial_idmapping() determines that this is not an idmapped mount
59 * we can simply return @kuid unchanged.
60 * If initial_idmapping() tells us that the filesystem is not mounted with an
61 * idmapping we know the value of @kuid won't change when calling
62 * from_kuid() so we can simply retrieve the value via __kuid_val()
65 * Return: @kuid mapped according to @idmap.
66 * If @kuid has no mapping in either @idmap or @fs_userns INVALID_UID is
70 vfsuid_t
make_vfsuid(struct mnt_idmap
*idmap
,
71 struct user_namespace
*fs_userns
,
76 if (idmap
== &nop_mnt_idmap
)
77 return VFSUIDT_INIT(kuid
);
78 if (initial_idmapping(fs_userns
))
79 uid
= __kuid_val(kuid
);
81 uid
= from_kuid(fs_userns
, kuid
);
83 return INVALID_VFSUID
;
84 return VFSUIDT_INIT_RAW(map_id_down(&idmap
->uid_map
, uid
));
86 EXPORT_SYMBOL_GPL(make_vfsuid
);
89 * make_vfsgid - map a filesystem kgid according to an idmapping
90 * @idmap: the mount's idmapping
91 * @fs_userns: the filesystem's idmapping
92 * @kgid : kgid to be mapped
94 * Take a @kgid and remap it from @fs_userns into @idmap. Use this
95 * function when preparing a @kgid to be reported to userspace.
97 * If initial_idmapping() determines that this is not an idmapped mount
98 * we can simply return @kgid unchanged.
99 * If initial_idmapping() tells us that the filesystem is not mounted with an
100 * idmapping we know the value of @kgid won't change when calling
101 * from_kgid() so we can simply retrieve the value via __kgid_val()
104 * Return: @kgid mapped according to @idmap.
105 * If @kgid has no mapping in either @idmap or @fs_userns INVALID_GID is
108 vfsgid_t
make_vfsgid(struct mnt_idmap
*idmap
,
109 struct user_namespace
*fs_userns
, kgid_t kgid
)
113 if (idmap
== &nop_mnt_idmap
)
114 return VFSGIDT_INIT(kgid
);
115 if (initial_idmapping(fs_userns
))
116 gid
= __kgid_val(kgid
);
118 gid
= from_kgid(fs_userns
, kgid
);
119 if (gid
== (gid_t
)-1)
120 return INVALID_VFSGID
;
121 return VFSGIDT_INIT_RAW(map_id_down(&idmap
->gid_map
, gid
));
123 EXPORT_SYMBOL_GPL(make_vfsgid
);
126 * from_vfsuid - map a vfsuid into the filesystem idmapping
127 * @idmap: the mount's idmapping
128 * @fs_userns: the filesystem's idmapping
129 * @vfsuid : vfsuid to be mapped
131 * Map @vfsuid into the filesystem idmapping. This function has to be used in
132 * order to e.g. write @vfsuid to inode->i_uid.
134 * Return: @vfsuid mapped into the filesystem idmapping
136 kuid_t
from_vfsuid(struct mnt_idmap
*idmap
,
137 struct user_namespace
*fs_userns
, vfsuid_t vfsuid
)
141 if (idmap
== &nop_mnt_idmap
)
142 return AS_KUIDT(vfsuid
);
143 uid
= map_id_up(&idmap
->uid_map
, __vfsuid_val(vfsuid
));
144 if (uid
== (uid_t
)-1)
146 if (initial_idmapping(fs_userns
))
147 return KUIDT_INIT(uid
);
148 return make_kuid(fs_userns
, uid
);
150 EXPORT_SYMBOL_GPL(from_vfsuid
);
153 * from_vfsgid - map a vfsgid into the filesystem idmapping
154 * @idmap: the mount's idmapping
155 * @fs_userns: the filesystem's idmapping
156 * @vfsgid : vfsgid to be mapped
158 * Map @vfsgid into the filesystem idmapping. This function has to be used in
159 * order to e.g. write @vfsgid to inode->i_gid.
161 * Return: @vfsgid mapped into the filesystem idmapping
163 kgid_t
from_vfsgid(struct mnt_idmap
*idmap
,
164 struct user_namespace
*fs_userns
, vfsgid_t vfsgid
)
168 if (idmap
== &nop_mnt_idmap
)
169 return AS_KGIDT(vfsgid
);
170 gid
= map_id_up(&idmap
->gid_map
, __vfsgid_val(vfsgid
));
171 if (gid
== (gid_t
)-1)
173 if (initial_idmapping(fs_userns
))
174 return KGIDT_INIT(gid
);
175 return make_kgid(fs_userns
, gid
);
177 EXPORT_SYMBOL_GPL(from_vfsgid
);
179 #ifdef CONFIG_MULTIUSER
181 * vfsgid_in_group_p() - check whether a vfsuid matches the caller's groups
182 * @vfsgid: the mnt gid to match
184 * This function can be used to determine whether @vfsuid matches any of the
187 * Return: 1 if vfsuid matches caller's groups, 0 if not.
189 int vfsgid_in_group_p(vfsgid_t vfsgid
)
191 return in_group_p(AS_KGIDT(vfsgid
));
194 int vfsgid_in_group_p(vfsgid_t vfsgid
)
199 EXPORT_SYMBOL_GPL(vfsgid_in_group_p
);
201 static int copy_mnt_idmap(struct uid_gid_map
*map_from
,
202 struct uid_gid_map
*map_to
)
204 struct uid_gid_extent
*forward
, *reverse
;
205 u32 nr_extents
= READ_ONCE(map_from
->nr_extents
);
206 /* Pairs with smp_wmb() when writing the idmapping. */
210 * Don't blindly copy @map_to into @map_from if nr_extents is
211 * smaller or equal to UID_GID_MAP_MAX_BASE_EXTENTS. Since we
212 * read @nr_extents someone could have written an idmapping and
213 * then we might end up with inconsistent data. So just don't do
220 * Here we know that nr_extents is greater than zero which means
221 * a map has been written. Since idmappings can't be changed
222 * once they have been written we know that we can safely copy
223 * from @map_to into @map_from.
226 if (nr_extents
<= UID_GID_MAP_MAX_BASE_EXTENTS
) {
231 forward
= kmemdup(map_from
->forward
,
232 nr_extents
* sizeof(struct uid_gid_extent
),
237 reverse
= kmemdup(map_from
->reverse
,
238 nr_extents
* sizeof(struct uid_gid_extent
),
246 * The idmapping isn't exposed anywhere so we don't need to care
247 * about ordering between extent pointers and @nr_extents
250 map_to
->forward
= forward
;
251 map_to
->reverse
= reverse
;
252 map_to
->nr_extents
= nr_extents
;
256 static void free_mnt_idmap(struct mnt_idmap
*idmap
)
258 if (idmap
->uid_map
.nr_extents
> UID_GID_MAP_MAX_BASE_EXTENTS
) {
259 kfree(idmap
->uid_map
.forward
);
260 kfree(idmap
->uid_map
.reverse
);
262 if (idmap
->gid_map
.nr_extents
> UID_GID_MAP_MAX_BASE_EXTENTS
) {
263 kfree(idmap
->gid_map
.forward
);
264 kfree(idmap
->gid_map
.reverse
);
269 struct mnt_idmap
*alloc_mnt_idmap(struct user_namespace
*mnt_userns
)
271 struct mnt_idmap
*idmap
;
274 idmap
= kzalloc(sizeof(struct mnt_idmap
), GFP_KERNEL_ACCOUNT
);
276 return ERR_PTR(-ENOMEM
);
278 refcount_set(&idmap
->count
, 1);
279 ret
= copy_mnt_idmap(&mnt_userns
->uid_map
, &idmap
->uid_map
);
281 ret
= copy_mnt_idmap(&mnt_userns
->gid_map
, &idmap
->gid_map
);
283 free_mnt_idmap(idmap
);
284 idmap
= ERR_PTR(ret
);
290 * mnt_idmap_get - get a reference to an idmapping
291 * @idmap: the idmap to bump the reference on
293 * If @idmap is not the @nop_mnt_idmap bump the reference count.
295 * Return: @idmap with reference count bumped if @not_mnt_idmap isn't passed.
297 struct mnt_idmap
*mnt_idmap_get(struct mnt_idmap
*idmap
)
299 if (idmap
!= &nop_mnt_idmap
)
300 refcount_inc(&idmap
->count
);
304 EXPORT_SYMBOL_GPL(mnt_idmap_get
);
307 * mnt_idmap_put - put a reference to an idmapping
308 * @idmap: the idmap to put the reference on
310 * If this is a non-initial idmapping, put the reference count when a mount is
311 * released and free it if we're the last user.
313 void mnt_idmap_put(struct mnt_idmap
*idmap
)
315 if (idmap
!= &nop_mnt_idmap
&& refcount_dec_and_test(&idmap
->count
))
316 free_mnt_idmap(idmap
);
318 EXPORT_SYMBOL_GPL(mnt_idmap_put
);