1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Encryption policy functions for per-file encryption support. 4 * 5 * Copyright (C) 2015, Google, Inc. 6 * Copyright (C) 2015, Motorola Mobility. 7 * 8 * Written by Michael Halcrow, 2015. 9 * Modified by Jaegeuk Kim, 2015. 10 */ 11 12 #include <linux/random.h> 13 #include <linux/string.h> 14 #include <linux/mount.h> 15 #include "fscrypt_private.h" 16 17 /* 18 * check whether an encryption policy is consistent with an encryption context 19 */ 20 static bool is_encryption_context_consistent_with_policy( 21 const struct fscrypt_context *ctx, 22 const struct fscrypt_policy *policy) 23 { 24 return memcmp(ctx->master_key_descriptor, policy->master_key_descriptor, 25 FS_KEY_DESCRIPTOR_SIZE) == 0 && 26 (ctx->flags == policy->flags) && 27 (ctx->contents_encryption_mode == 28 policy->contents_encryption_mode) && 29 (ctx->filenames_encryption_mode == 30 policy->filenames_encryption_mode); 31 } 32 33 static int create_encryption_context_from_policy(struct inode *inode, 34 const struct fscrypt_policy *policy) 35 { 36 struct fscrypt_context ctx; 37 38 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1; 39 memcpy(ctx.master_key_descriptor, policy->master_key_descriptor, 40 FS_KEY_DESCRIPTOR_SIZE); 41 42 if (!fscrypt_valid_enc_modes(policy->contents_encryption_mode, 43 policy->filenames_encryption_mode)) 44 return -EINVAL; 45 46 if (policy->flags & ~FS_POLICY_FLAGS_VALID) 47 return -EINVAL; 48 49 ctx.contents_encryption_mode = policy->contents_encryption_mode; 50 ctx.filenames_encryption_mode = policy->filenames_encryption_mode; 51 ctx.flags = policy->flags; 52 BUILD_BUG_ON(sizeof(ctx.nonce) != FS_KEY_DERIVATION_NONCE_SIZE); 53 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE); 54 55 return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL); 56 } 57 58 int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg) 59 { 60 struct fscrypt_policy policy; 61 struct inode *inode = file_inode(filp); 62 int ret; 63 struct fscrypt_context ctx; 64 65 if (copy_from_user(&policy, arg, sizeof(policy))) 66 return -EFAULT; 67 68 if (!inode_owner_or_capable(inode)) 69 return -EACCES; 70 71 if (policy.version != 0) 72 return -EINVAL; 73 74 ret = mnt_want_write_file(filp); 75 if (ret) 76 return ret; 77 78 inode_lock(inode); 79 80 ret = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx)); 81 if (ret == -ENODATA) { 82 if (!S_ISDIR(inode->i_mode)) 83 ret = -ENOTDIR; 84 else if (!inode->i_sb->s_cop->empty_dir(inode)) 85 ret = -ENOTEMPTY; 86 else 87 ret = create_encryption_context_from_policy(inode, 88 &policy); 89 } else if (ret == sizeof(ctx) && 90 is_encryption_context_consistent_with_policy(&ctx, 91 &policy)) { 92 /* The file already uses the same encryption policy. */ 93 ret = 0; 94 } else if (ret >= 0 || ret == -ERANGE) { 95 /* The file already uses a different encryption policy. */ 96 ret = -EEXIST; 97 } 98 99 inode_unlock(inode); 100 101 mnt_drop_write_file(filp); 102 return ret; 103 } 104 EXPORT_SYMBOL(fscrypt_ioctl_set_policy); 105 106 int fscrypt_ioctl_get_policy(struct file *filp, void __user *arg) 107 { 108 struct inode *inode = file_inode(filp); 109 struct fscrypt_context ctx; 110 struct fscrypt_policy policy; 111 int res; 112 113 if (!IS_ENCRYPTED(inode)) 114 return -ENODATA; 115 116 res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx)); 117 if (res < 0 && res != -ERANGE) 118 return res; 119 if (res != sizeof(ctx)) 120 return -EINVAL; 121 if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1) 122 return -EINVAL; 123 124 policy.version = 0; 125 policy.contents_encryption_mode = ctx.contents_encryption_mode; 126 policy.filenames_encryption_mode = ctx.filenames_encryption_mode; 127 policy.flags = ctx.flags; 128 memcpy(policy.master_key_descriptor, ctx.master_key_descriptor, 129 FS_KEY_DESCRIPTOR_SIZE); 130 131 if (copy_to_user(arg, &policy, sizeof(policy))) 132 return -EFAULT; 133 return 0; 134 } 135 EXPORT_SYMBOL(fscrypt_ioctl_get_policy); 136 137 /** 138 * fscrypt_has_permitted_context() - is a file's encryption policy permitted 139 * within its directory? 140 * 141 * @parent: inode for parent directory 142 * @child: inode for file being looked up, opened, or linked into @parent 143 * 144 * Filesystems must call this before permitting access to an inode in a 145 * situation where the parent directory is encrypted (either before allowing 146 * ->lookup() to succeed, or for a regular file before allowing it to be opened) 147 * and before any operation that involves linking an inode into an encrypted 148 * directory, including link, rename, and cross rename. It enforces the 149 * constraint that within a given encrypted directory tree, all files use the 150 * same encryption policy. The pre-access check is needed to detect potentially 151 * malicious offline violations of this constraint, while the link and rename 152 * checks are needed to prevent online violations of this constraint. 153 * 154 * Return: 1 if permitted, 0 if forbidden. If forbidden, the caller must fail 155 * the filesystem operation with EPERM. 156 */ 157 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child) 158 { 159 const struct fscrypt_operations *cops = parent->i_sb->s_cop; 160 const struct fscrypt_info *parent_ci, *child_ci; 161 struct fscrypt_context parent_ctx, child_ctx; 162 int res; 163 164 /* No restrictions on file types which are never encrypted */ 165 if (!S_ISREG(child->i_mode) && !S_ISDIR(child->i_mode) && 166 !S_ISLNK(child->i_mode)) 167 return 1; 168 169 /* No restrictions if the parent directory is unencrypted */ 170 if (!IS_ENCRYPTED(parent)) 171 return 1; 172 173 /* Encrypted directories must not contain unencrypted files */ 174 if (!IS_ENCRYPTED(child)) 175 return 0; 176 177 /* 178 * Both parent and child are encrypted, so verify they use the same 179 * encryption policy. Compare the fscrypt_info structs if the keys are 180 * available, otherwise retrieve and compare the fscrypt_contexts. 181 * 182 * Note that the fscrypt_context retrieval will be required frequently 183 * when accessing an encrypted directory tree without the key. 184 * Performance-wise this is not a big deal because we already don't 185 * really optimize for file access without the key (to the extent that 186 * such access is even possible), given that any attempted access 187 * already causes a fscrypt_context retrieval and keyring search. 188 * 189 * In any case, if an unexpected error occurs, fall back to "forbidden". 190 */ 191 192 res = fscrypt_get_encryption_info(parent); 193 if (res) 194 return 0; 195 res = fscrypt_get_encryption_info(child); 196 if (res) 197 return 0; 198 parent_ci = parent->i_crypt_info; 199 child_ci = child->i_crypt_info; 200 201 if (parent_ci && child_ci) { 202 return memcmp(parent_ci->ci_master_key, child_ci->ci_master_key, 203 FS_KEY_DESCRIPTOR_SIZE) == 0 && 204 (parent_ci->ci_data_mode == child_ci->ci_data_mode) && 205 (parent_ci->ci_filename_mode == 206 child_ci->ci_filename_mode) && 207 (parent_ci->ci_flags == child_ci->ci_flags); 208 } 209 210 res = cops->get_context(parent, &parent_ctx, sizeof(parent_ctx)); 211 if (res != sizeof(parent_ctx)) 212 return 0; 213 214 res = cops->get_context(child, &child_ctx, sizeof(child_ctx)); 215 if (res != sizeof(child_ctx)) 216 return 0; 217 218 return memcmp(parent_ctx.master_key_descriptor, 219 child_ctx.master_key_descriptor, 220 FS_KEY_DESCRIPTOR_SIZE) == 0 && 221 (parent_ctx.contents_encryption_mode == 222 child_ctx.contents_encryption_mode) && 223 (parent_ctx.filenames_encryption_mode == 224 child_ctx.filenames_encryption_mode) && 225 (parent_ctx.flags == child_ctx.flags); 226 } 227 EXPORT_SYMBOL(fscrypt_has_permitted_context); 228 229 /** 230 * fscrypt_inherit_context() - Sets a child context from its parent 231 * @parent: Parent inode from which the context is inherited. 232 * @child: Child inode that inherits the context from @parent. 233 * @fs_data: private data given by FS. 234 * @preload: preload child i_crypt_info if true 235 * 236 * Return: 0 on success, -errno on failure 237 */ 238 int fscrypt_inherit_context(struct inode *parent, struct inode *child, 239 void *fs_data, bool preload) 240 { 241 struct fscrypt_context ctx; 242 struct fscrypt_info *ci; 243 int res; 244 245 res = fscrypt_get_encryption_info(parent); 246 if (res < 0) 247 return res; 248 249 ci = parent->i_crypt_info; 250 if (ci == NULL) 251 return -ENOKEY; 252 253 ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1; 254 ctx.contents_encryption_mode = ci->ci_data_mode; 255 ctx.filenames_encryption_mode = ci->ci_filename_mode; 256 ctx.flags = ci->ci_flags; 257 memcpy(ctx.master_key_descriptor, ci->ci_master_key, 258 FS_KEY_DESCRIPTOR_SIZE); 259 get_random_bytes(ctx.nonce, FS_KEY_DERIVATION_NONCE_SIZE); 260 BUILD_BUG_ON(sizeof(ctx) != FSCRYPT_SET_CONTEXT_MAX_SIZE); 261 res = parent->i_sb->s_cop->set_context(child, &ctx, 262 sizeof(ctx), fs_data); 263 if (res) 264 return res; 265 return preload ? fscrypt_get_encryption_info(child): 0; 266 } 267 EXPORT_SYMBOL(fscrypt_inherit_context); 268