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