1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_MNT_IDMAPPING_H
3 #define _LINUX_MNT_IDMAPPING_H
4
5 #include <linux/types.h>
6 #include <linux/uidgid.h>
7
8 struct user_namespace;
9 /*
10 * Carries the initial idmapping of 0:0:4294967295 which is an identity
11 * mapping. This means that {g,u}id 0 is mapped to {g,u}id 0, {g,u}id 1 is
12 * mapped to {g,u}id 1, [...], {g,u}id 1000 to {g,u}id 1000, [...].
13 */
14 extern struct user_namespace init_user_ns;
15
16 /**
17 * initial_idmapping - check whether this is the initial mapping
18 * @ns: idmapping to check
19 *
20 * Check whether this is the initial mapping, mapping 0 to 0, 1 to 1,
21 * [...], 1000 to 1000 [...].
22 *
23 * Return: true if this is the initial mapping, false if not.
24 */
initial_idmapping(const struct user_namespace * ns)25 static inline bool initial_idmapping(const struct user_namespace *ns)
26 {
27 return ns == &init_user_ns;
28 }
29
30 /**
31 * no_idmapping - check whether we can skip remapping a kuid/gid
32 * @mnt_userns: the mount's idmapping
33 * @fs_userns: the filesystem's idmapping
34 *
35 * This function can be used to check whether a remapping between two
36 * idmappings is required.
37 * An idmapped mount is a mount that has an idmapping attached to it that
38 * is different from the filsystem's idmapping and the initial idmapping.
39 * If the initial mapping is used or the idmapping of the mount and the
40 * filesystem are identical no remapping is required.
41 *
42 * Return: true if remapping can be skipped, false if not.
43 */
no_idmapping(const struct user_namespace * mnt_userns,const struct user_namespace * fs_userns)44 static inline bool no_idmapping(const struct user_namespace *mnt_userns,
45 const struct user_namespace *fs_userns)
46 {
47 return initial_idmapping(mnt_userns) || mnt_userns == fs_userns;
48 }
49
50 /**
51 * mapped_kuid_fs - map a filesystem kuid into a mnt_userns
52 * @mnt_userns: the mount's idmapping
53 * @fs_userns: the filesystem's idmapping
54 * @kuid : kuid to be mapped
55 *
56 * Take a @kuid and remap it from @fs_userns into @mnt_userns. Use this
57 * function when preparing a @kuid to be reported to userspace.
58 *
59 * If no_idmapping() determines that this is not an idmapped mount we can
60 * simply return @kuid unchanged.
61 * If initial_idmapping() tells us that the filesystem is not mounted with an
62 * idmapping we know the value of @kuid won't change when calling
63 * from_kuid() so we can simply retrieve the value via __kuid_val()
64 * directly.
65 *
66 * Return: @kuid mapped according to @mnt_userns.
67 * If @kuid has no mapping in either @mnt_userns or @fs_userns INVALID_UID is
68 * returned.
69 */
mapped_kuid_fs(struct user_namespace * mnt_userns,struct user_namespace * fs_userns,kuid_t kuid)70 static inline kuid_t mapped_kuid_fs(struct user_namespace *mnt_userns,
71 struct user_namespace *fs_userns,
72 kuid_t kuid)
73 {
74 uid_t uid;
75
76 if (no_idmapping(mnt_userns, fs_userns))
77 return kuid;
78 if (initial_idmapping(fs_userns))
79 uid = __kuid_val(kuid);
80 else
81 uid = from_kuid(fs_userns, kuid);
82 if (uid == (uid_t)-1)
83 return INVALID_UID;
84 return make_kuid(mnt_userns, uid);
85 }
86
87 /**
88 * mapped_kgid_fs - map a filesystem kgid into a mnt_userns
89 * @mnt_userns: the mount's idmapping
90 * @fs_userns: the filesystem's idmapping
91 * @kgid : kgid to be mapped
92 *
93 * Take a @kgid and remap it from @fs_userns into @mnt_userns. Use this
94 * function when preparing a @kgid to be reported to userspace.
95 *
96 * If no_idmapping() determines that this is not an idmapped mount we can
97 * simply return @kgid unchanged.
98 * If initial_idmapping() tells us that the filesystem is not mounted with an
99 * idmapping we know the value of @kgid won't change when calling
100 * from_kgid() so we can simply retrieve the value via __kgid_val()
101 * directly.
102 *
103 * Return: @kgid mapped according to @mnt_userns.
104 * If @kgid has no mapping in either @mnt_userns or @fs_userns INVALID_GID is
105 * returned.
106 */
mapped_kgid_fs(struct user_namespace * mnt_userns,struct user_namespace * fs_userns,kgid_t kgid)107 static inline kgid_t mapped_kgid_fs(struct user_namespace *mnt_userns,
108 struct user_namespace *fs_userns,
109 kgid_t kgid)
110 {
111 gid_t gid;
112
113 if (no_idmapping(mnt_userns, fs_userns))
114 return kgid;
115 if (initial_idmapping(fs_userns))
116 gid = __kgid_val(kgid);
117 else
118 gid = from_kgid(fs_userns, kgid);
119 if (gid == (gid_t)-1)
120 return INVALID_GID;
121 return make_kgid(mnt_userns, gid);
122 }
123
124 /**
125 * mapped_kuid_user - map a user kuid into a mnt_userns
126 * @mnt_userns: the mount's idmapping
127 * @fs_userns: the filesystem's idmapping
128 * @kuid : kuid to be mapped
129 *
130 * Use the idmapping of @mnt_userns to remap a @kuid into @fs_userns. Use this
131 * function when preparing a @kuid to be written to disk or inode.
132 *
133 * If no_idmapping() determines that this is not an idmapped mount we can
134 * simply return @kuid unchanged.
135 * If initial_idmapping() tells us that the filesystem is not mounted with an
136 * idmapping we know the value of @kuid won't change when calling
137 * make_kuid() so we can simply retrieve the value via KUIDT_INIT()
138 * directly.
139 *
140 * Return: @kuid mapped according to @mnt_userns.
141 * If @kuid has no mapping in either @mnt_userns or @fs_userns INVALID_UID is
142 * returned.
143 */
mapped_kuid_user(struct user_namespace * mnt_userns,struct user_namespace * fs_userns,kuid_t kuid)144 static inline kuid_t mapped_kuid_user(struct user_namespace *mnt_userns,
145 struct user_namespace *fs_userns,
146 kuid_t kuid)
147 {
148 uid_t uid;
149
150 if (no_idmapping(mnt_userns, fs_userns))
151 return kuid;
152 uid = from_kuid(mnt_userns, kuid);
153 if (uid == (uid_t)-1)
154 return INVALID_UID;
155 if (initial_idmapping(fs_userns))
156 return KUIDT_INIT(uid);
157 return make_kuid(fs_userns, uid);
158 }
159
160 /**
161 * mapped_kgid_user - map a user kgid into a mnt_userns
162 * @mnt_userns: the mount's idmapping
163 * @fs_userns: the filesystem's idmapping
164 * @kgid : kgid to be mapped
165 *
166 * Use the idmapping of @mnt_userns to remap a @kgid into @fs_userns. Use this
167 * function when preparing a @kgid to be written to disk or inode.
168 *
169 * If no_idmapping() determines that this is not an idmapped mount we can
170 * simply return @kgid unchanged.
171 * If initial_idmapping() tells us that the filesystem is not mounted with an
172 * idmapping we know the value of @kgid won't change when calling
173 * make_kgid() so we can simply retrieve the value via KGIDT_INIT()
174 * directly.
175 *
176 * Return: @kgid mapped according to @mnt_userns.
177 * If @kgid has no mapping in either @mnt_userns or @fs_userns INVALID_GID is
178 * returned.
179 */
mapped_kgid_user(struct user_namespace * mnt_userns,struct user_namespace * fs_userns,kgid_t kgid)180 static inline kgid_t mapped_kgid_user(struct user_namespace *mnt_userns,
181 struct user_namespace *fs_userns,
182 kgid_t kgid)
183 {
184 gid_t gid;
185
186 if (no_idmapping(mnt_userns, fs_userns))
187 return kgid;
188 gid = from_kgid(mnt_userns, kgid);
189 if (gid == (gid_t)-1)
190 return INVALID_GID;
191 if (initial_idmapping(fs_userns))
192 return KGIDT_INIT(gid);
193 return make_kgid(fs_userns, gid);
194 }
195
196 /**
197 * mapped_fsuid - return caller's fsuid mapped up into a mnt_userns
198 * @mnt_userns: the mount's idmapping
199 * @fs_userns: the filesystem's idmapping
200 *
201 * Use this helper to initialize a new vfs or filesystem object based on
202 * the caller's fsuid. A common example is initializing the i_uid field of
203 * a newly allocated inode triggered by a creation event such as mkdir or
204 * O_CREAT. Other examples include the allocation of quotas for a specific
205 * user.
206 *
207 * Return: the caller's current fsuid mapped up according to @mnt_userns.
208 */
mapped_fsuid(struct user_namespace * mnt_userns,struct user_namespace * fs_userns)209 static inline kuid_t mapped_fsuid(struct user_namespace *mnt_userns,
210 struct user_namespace *fs_userns)
211 {
212 return mapped_kuid_user(mnt_userns, fs_userns, current_fsuid());
213 }
214
215 /**
216 * mapped_fsgid - return caller's fsgid mapped up into a mnt_userns
217 * @mnt_userns: the mount's idmapping
218 * @fs_userns: the filesystem's idmapping
219 *
220 * Use this helper to initialize a new vfs or filesystem object based on
221 * the caller's fsgid. A common example is initializing the i_gid field of
222 * a newly allocated inode triggered by a creation event such as mkdir or
223 * O_CREAT. Other examples include the allocation of quotas for a specific
224 * user.
225 *
226 * Return: the caller's current fsgid mapped up according to @mnt_userns.
227 */
mapped_fsgid(struct user_namespace * mnt_userns,struct user_namespace * fs_userns)228 static inline kgid_t mapped_fsgid(struct user_namespace *mnt_userns,
229 struct user_namespace *fs_userns)
230 {
231 return mapped_kgid_user(mnt_userns, fs_userns, current_fsgid());
232 }
233
234 #endif /* _LINUX_MNT_IDMAPPING_H */
235