Christian Brauner | 3707d84 | 2023-01-13 12:49:33 +0100 | [diff] [blame] | 1 | // SPDX-License-Identifier: GPL-2.0 |
| 2 | /* Copyright (c) 2022 Christian Brauner <brauner@kernel.org> */ |
| 3 | |
| 4 | #include <linux/cred.h> |
| 5 | #include <linux/fs.h> |
| 6 | #include <linux/mnt_idmapping.h> |
| 7 | #include <linux/slab.h> |
| 8 | #include <linux/user_namespace.h> |
| 9 | |
| 10 | #include "internal.h" |
| 11 | |
| 12 | struct mnt_idmap { |
| 13 | struct user_namespace *owner; |
| 14 | refcount_t count; |
| 15 | }; |
| 16 | |
| 17 | /* |
| 18 | * Carries the initial idmapping of 0:0:4294967295 which is an identity |
| 19 | * mapping. This means that {g,u}id 0 is mapped to {g,u}id 0, {g,u}id 1 is |
| 20 | * mapped to {g,u}id 1, [...], {g,u}id 1000 to {g,u}id 1000, [...]. |
| 21 | */ |
| 22 | struct mnt_idmap nop_mnt_idmap = { |
| 23 | .owner = &init_user_ns, |
| 24 | .count = REFCOUNT_INIT(1), |
| 25 | }; |
| 26 | EXPORT_SYMBOL_GPL(nop_mnt_idmap); |
| 27 | |
| 28 | /** |
| 29 | * check_fsmapping - check whether an mount idmapping is allowed |
| 30 | * @idmap: idmap of the relevent mount |
| 31 | * @sb: super block of the filesystem |
| 32 | * |
| 33 | * Return: true if @idmap is allowed, false if not. |
| 34 | */ |
| 35 | bool check_fsmapping(const struct mnt_idmap *idmap, |
| 36 | const struct super_block *sb) |
| 37 | { |
| 38 | return idmap->owner != sb->s_user_ns; |
| 39 | } |
| 40 | |
| 41 | /** |
| 42 | * initial_idmapping - check whether this is the initial mapping |
| 43 | * @ns: idmapping to check |
| 44 | * |
| 45 | * Check whether this is the initial mapping, mapping 0 to 0, 1 to 1, |
| 46 | * [...], 1000 to 1000 [...]. |
| 47 | * |
| 48 | * Return: true if this is the initial mapping, false if not. |
| 49 | */ |
| 50 | static inline bool initial_idmapping(const struct user_namespace *ns) |
| 51 | { |
| 52 | return ns == &init_user_ns; |
| 53 | } |
| 54 | |
| 55 | /** |
| 56 | * no_idmapping - check whether we can skip remapping a kuid/gid |
| 57 | * @mnt_userns: the mount's idmapping |
| 58 | * @fs_userns: the filesystem's idmapping |
| 59 | * |
| 60 | * This function can be used to check whether a remapping between two |
| 61 | * idmappings is required. |
| 62 | * An idmapped mount is a mount that has an idmapping attached to it that |
| 63 | * is different from the filsystem's idmapping and the initial idmapping. |
| 64 | * If the initial mapping is used or the idmapping of the mount and the |
| 65 | * filesystem are identical no remapping is required. |
| 66 | * |
| 67 | * Return: true if remapping can be skipped, false if not. |
| 68 | */ |
| 69 | static inline bool no_idmapping(const struct user_namespace *mnt_userns, |
| 70 | const struct user_namespace *fs_userns) |
| 71 | { |
| 72 | return initial_idmapping(mnt_userns) || mnt_userns == fs_userns; |
| 73 | } |
| 74 | |
| 75 | /** |
| 76 | * make_vfsuid - map a filesystem kuid according to an idmapping |
| 77 | * @idmap: the mount's idmapping |
| 78 | * @fs_userns: the filesystem's idmapping |
| 79 | * @kuid : kuid to be mapped |
| 80 | * |
| 81 | * Take a @kuid and remap it from @fs_userns into @idmap. Use this |
| 82 | * function when preparing a @kuid to be reported to userspace. |
| 83 | * |
| 84 | * If no_idmapping() determines that this is not an idmapped mount we can |
| 85 | * simply return @kuid unchanged. |
| 86 | * If initial_idmapping() tells us that the filesystem is not mounted with an |
| 87 | * idmapping we know the value of @kuid won't change when calling |
| 88 | * from_kuid() so we can simply retrieve the value via __kuid_val() |
| 89 | * directly. |
| 90 | * |
| 91 | * Return: @kuid mapped according to @idmap. |
| 92 | * If @kuid has no mapping in either @idmap or @fs_userns INVALID_UID is |
| 93 | * returned. |
| 94 | */ |
| 95 | |
| 96 | vfsuid_t make_vfsuid(struct mnt_idmap *idmap, |
| 97 | struct user_namespace *fs_userns, |
| 98 | kuid_t kuid) |
| 99 | { |
| 100 | uid_t uid; |
| 101 | struct user_namespace *mnt_userns = idmap->owner; |
| 102 | |
| 103 | if (no_idmapping(mnt_userns, fs_userns)) |
| 104 | return VFSUIDT_INIT(kuid); |
| 105 | if (initial_idmapping(fs_userns)) |
| 106 | uid = __kuid_val(kuid); |
| 107 | else |
| 108 | uid = from_kuid(fs_userns, kuid); |
| 109 | if (uid == (uid_t)-1) |
| 110 | return INVALID_VFSUID; |
| 111 | return VFSUIDT_INIT(make_kuid(mnt_userns, uid)); |
| 112 | } |
| 113 | EXPORT_SYMBOL_GPL(make_vfsuid); |
| 114 | |
| 115 | /** |
| 116 | * make_vfsgid - map a filesystem kgid according to an idmapping |
| 117 | * @idmap: the mount's idmapping |
| 118 | * @fs_userns: the filesystem's idmapping |
| 119 | * @kgid : kgid to be mapped |
| 120 | * |
| 121 | * Take a @kgid and remap it from @fs_userns into @idmap. Use this |
| 122 | * function when preparing a @kgid to be reported to userspace. |
| 123 | * |
| 124 | * If no_idmapping() determines that this is not an idmapped mount we can |
| 125 | * simply return @kgid unchanged. |
| 126 | * If initial_idmapping() tells us that the filesystem is not mounted with an |
| 127 | * idmapping we know the value of @kgid won't change when calling |
| 128 | * from_kgid() so we can simply retrieve the value via __kgid_val() |
| 129 | * directly. |
| 130 | * |
| 131 | * Return: @kgid mapped according to @idmap. |
| 132 | * If @kgid has no mapping in either @idmap or @fs_userns INVALID_GID is |
| 133 | * returned. |
| 134 | */ |
| 135 | vfsgid_t make_vfsgid(struct mnt_idmap *idmap, |
| 136 | struct user_namespace *fs_userns, kgid_t kgid) |
| 137 | { |
| 138 | gid_t gid; |
| 139 | struct user_namespace *mnt_userns = idmap->owner; |
| 140 | |
| 141 | if (no_idmapping(mnt_userns, fs_userns)) |
| 142 | return VFSGIDT_INIT(kgid); |
| 143 | if (initial_idmapping(fs_userns)) |
| 144 | gid = __kgid_val(kgid); |
| 145 | else |
| 146 | gid = from_kgid(fs_userns, kgid); |
| 147 | if (gid == (gid_t)-1) |
| 148 | return INVALID_VFSGID; |
| 149 | return VFSGIDT_INIT(make_kgid(mnt_userns, gid)); |
| 150 | } |
| 151 | EXPORT_SYMBOL_GPL(make_vfsgid); |
| 152 | |
| 153 | /** |
| 154 | * from_vfsuid - map a vfsuid into the filesystem idmapping |
| 155 | * @idmap: the mount's idmapping |
| 156 | * @fs_userns: the filesystem's idmapping |
| 157 | * @vfsuid : vfsuid to be mapped |
| 158 | * |
| 159 | * Map @vfsuid into the filesystem idmapping. This function has to be used in |
| 160 | * order to e.g. write @vfsuid to inode->i_uid. |
| 161 | * |
| 162 | * Return: @vfsuid mapped into the filesystem idmapping |
| 163 | */ |
| 164 | kuid_t from_vfsuid(struct mnt_idmap *idmap, |
| 165 | struct user_namespace *fs_userns, vfsuid_t vfsuid) |
| 166 | { |
| 167 | uid_t uid; |
| 168 | struct user_namespace *mnt_userns = idmap->owner; |
| 169 | |
| 170 | if (no_idmapping(mnt_userns, fs_userns)) |
| 171 | return AS_KUIDT(vfsuid); |
| 172 | uid = from_kuid(mnt_userns, AS_KUIDT(vfsuid)); |
| 173 | if (uid == (uid_t)-1) |
| 174 | return INVALID_UID; |
| 175 | if (initial_idmapping(fs_userns)) |
| 176 | return KUIDT_INIT(uid); |
| 177 | return make_kuid(fs_userns, uid); |
| 178 | } |
| 179 | EXPORT_SYMBOL_GPL(from_vfsuid); |
| 180 | |
| 181 | /** |
| 182 | * from_vfsgid - map a vfsgid into the filesystem idmapping |
| 183 | * @idmap: the mount's idmapping |
| 184 | * @fs_userns: the filesystem's idmapping |
| 185 | * @vfsgid : vfsgid to be mapped |
| 186 | * |
| 187 | * Map @vfsgid into the filesystem idmapping. This function has to be used in |
| 188 | * order to e.g. write @vfsgid to inode->i_gid. |
| 189 | * |
| 190 | * Return: @vfsgid mapped into the filesystem idmapping |
| 191 | */ |
| 192 | kgid_t from_vfsgid(struct mnt_idmap *idmap, |
| 193 | struct user_namespace *fs_userns, vfsgid_t vfsgid) |
| 194 | { |
| 195 | gid_t gid; |
| 196 | struct user_namespace *mnt_userns = idmap->owner; |
| 197 | |
| 198 | if (no_idmapping(mnt_userns, fs_userns)) |
| 199 | return AS_KGIDT(vfsgid); |
| 200 | gid = from_kgid(mnt_userns, AS_KGIDT(vfsgid)); |
| 201 | if (gid == (gid_t)-1) |
| 202 | return INVALID_GID; |
| 203 | if (initial_idmapping(fs_userns)) |
| 204 | return KGIDT_INIT(gid); |
| 205 | return make_kgid(fs_userns, gid); |
| 206 | } |
| 207 | EXPORT_SYMBOL_GPL(from_vfsgid); |
| 208 | |
| 209 | #ifdef CONFIG_MULTIUSER |
| 210 | /** |
| 211 | * vfsgid_in_group_p() - check whether a vfsuid matches the caller's groups |
| 212 | * @vfsgid: the mnt gid to match |
| 213 | * |
| 214 | * This function can be used to determine whether @vfsuid matches any of the |
| 215 | * caller's groups. |
| 216 | * |
| 217 | * Return: 1 if vfsuid matches caller's groups, 0 if not. |
| 218 | */ |
| 219 | int vfsgid_in_group_p(vfsgid_t vfsgid) |
| 220 | { |
| 221 | return in_group_p(AS_KGIDT(vfsgid)); |
| 222 | } |
| 223 | #else |
| 224 | int vfsgid_in_group_p(vfsgid_t vfsgid) |
| 225 | { |
| 226 | return 1; |
| 227 | } |
| 228 | #endif |
| 229 | EXPORT_SYMBOL_GPL(vfsgid_in_group_p); |
| 230 | |
| 231 | struct mnt_idmap *alloc_mnt_idmap(struct user_namespace *mnt_userns) |
| 232 | { |
| 233 | struct mnt_idmap *idmap; |
| 234 | |
| 235 | idmap = kzalloc(sizeof(struct mnt_idmap), GFP_KERNEL_ACCOUNT); |
| 236 | if (!idmap) |
| 237 | return ERR_PTR(-ENOMEM); |
| 238 | |
| 239 | idmap->owner = get_user_ns(mnt_userns); |
| 240 | refcount_set(&idmap->count, 1); |
| 241 | return idmap; |
| 242 | } |
| 243 | |
| 244 | /** |
| 245 | * mnt_idmap_get - get a reference to an idmapping |
| 246 | * @idmap: the idmap to bump the reference on |
| 247 | * |
| 248 | * If @idmap is not the @nop_mnt_idmap bump the reference count. |
| 249 | * |
| 250 | * Return: @idmap with reference count bumped if @not_mnt_idmap isn't passed. |
| 251 | */ |
| 252 | struct mnt_idmap *mnt_idmap_get(struct mnt_idmap *idmap) |
| 253 | { |
| 254 | if (idmap != &nop_mnt_idmap) |
| 255 | refcount_inc(&idmap->count); |
| 256 | |
| 257 | return idmap; |
| 258 | } |
| 259 | |
| 260 | /** |
| 261 | * mnt_idmap_put - put a reference to an idmapping |
| 262 | * @idmap: the idmap to put the reference on |
| 263 | * |
| 264 | * If this is a non-initial idmapping, put the reference count when a mount is |
| 265 | * released and free it if we're the last user. |
| 266 | */ |
| 267 | void mnt_idmap_put(struct mnt_idmap *idmap) |
| 268 | { |
| 269 | if (idmap != &nop_mnt_idmap && refcount_dec_and_test(&idmap->count)) { |
| 270 | put_user_ns(idmap->owner); |
| 271 | kfree(idmap); |
| 272 | } |
| 273 | } |