1 /* 2 * fs/crypto/hooks.c 3 * 4 * Encryption hooks for higher-level filesystem operations. 5 */ 6 7 #include <linux/ratelimit.h> 8 #include "fscrypt_private.h" 9 10 /** 11 * fscrypt_file_open - prepare to open a possibly-encrypted regular file 12 * @inode: the inode being opened 13 * @filp: the struct file being set up 14 * 15 * Currently, an encrypted regular file can only be opened if its encryption key 16 * is available; access to the raw encrypted contents is not supported. 17 * Therefore, we first set up the inode's encryption key (if not already done) 18 * and return an error if it's unavailable. 19 * 20 * We also verify that if the parent directory (from the path via which the file 21 * is being opened) is encrypted, then the inode being opened uses the same 22 * encryption policy. This is needed as part of the enforcement that all files 23 * in an encrypted directory tree use the same encryption policy, as a 24 * protection against certain types of offline attacks. Note that this check is 25 * needed even when opening an *unencrypted* file, since it's forbidden to have 26 * an unencrypted file in an encrypted directory. 27 * 28 * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code 29 */ 30 int fscrypt_file_open(struct inode *inode, struct file *filp) 31 { 32 int err; 33 struct dentry *dir; 34 35 err = fscrypt_require_key(inode); 36 if (err) 37 return err; 38 39 dir = dget_parent(file_dentry(filp)); 40 if (IS_ENCRYPTED(d_inode(dir)) && 41 !fscrypt_has_permitted_context(d_inode(dir), inode)) { 42 pr_warn_ratelimited("fscrypt: inconsistent encryption contexts: %lu/%lu", 43 d_inode(dir)->i_ino, inode->i_ino); 44 err = -EPERM; 45 } 46 dput(dir); 47 return err; 48 } 49 EXPORT_SYMBOL_GPL(fscrypt_file_open); 50 51 int __fscrypt_prepare_link(struct inode *inode, struct inode *dir) 52 { 53 int err; 54 55 err = fscrypt_require_key(dir); 56 if (err) 57 return err; 58 59 if (!fscrypt_has_permitted_context(dir, inode)) 60 return -EPERM; 61 62 return 0; 63 } 64 EXPORT_SYMBOL_GPL(__fscrypt_prepare_link); 65 66 int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry, 67 struct inode *new_dir, struct dentry *new_dentry, 68 unsigned int flags) 69 { 70 int err; 71 72 err = fscrypt_require_key(old_dir); 73 if (err) 74 return err; 75 76 err = fscrypt_require_key(new_dir); 77 if (err) 78 return err; 79 80 if (old_dir != new_dir) { 81 if (IS_ENCRYPTED(new_dir) && 82 !fscrypt_has_permitted_context(new_dir, 83 d_inode(old_dentry))) 84 return -EPERM; 85 86 if ((flags & RENAME_EXCHANGE) && 87 IS_ENCRYPTED(old_dir) && 88 !fscrypt_has_permitted_context(old_dir, 89 d_inode(new_dentry))) 90 return -EPERM; 91 } 92 return 0; 93 } 94 EXPORT_SYMBOL_GPL(__fscrypt_prepare_rename); 95 96 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry) 97 { 98 int err = fscrypt_get_encryption_info(dir); 99 100 if (err) 101 return err; 102 103 if (fscrypt_has_encryption_key(dir)) { 104 spin_lock(&dentry->d_lock); 105 dentry->d_flags |= DCACHE_ENCRYPTED_WITH_KEY; 106 spin_unlock(&dentry->d_lock); 107 } 108 109 d_set_d_op(dentry, &fscrypt_d_ops); 110 return 0; 111 } 112 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup); 113 114 int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len, 115 unsigned int max_len, 116 struct fscrypt_str *disk_link) 117 { 118 int err; 119 120 /* 121 * To calculate the size of the encrypted symlink target we need to know 122 * the amount of NUL padding, which is determined by the flags set in 123 * the encryption policy which will be inherited from the directory. 124 * The easiest way to get access to this is to just load the directory's 125 * fscrypt_info, since we'll need it to create the dir_entry anyway. 126 * 127 * Note: in test_dummy_encryption mode, @dir may be unencrypted. 128 */ 129 err = fscrypt_get_encryption_info(dir); 130 if (err) 131 return err; 132 if (!fscrypt_has_encryption_key(dir)) 133 return -ENOKEY; 134 135 /* 136 * Calculate the size of the encrypted symlink and verify it won't 137 * exceed max_len. Note that for historical reasons, encrypted symlink 138 * targets are prefixed with the ciphertext length, despite this 139 * actually being redundant with i_size. This decreases by 2 bytes the 140 * longest symlink target we can accept. 141 * 142 * We could recover 1 byte by not counting a null terminator, but 143 * counting it (even though it is meaningless for ciphertext) is simpler 144 * for now since filesystems will assume it is there and subtract it. 145 */ 146 if (sizeof(struct fscrypt_symlink_data) + len > max_len) 147 return -ENAMETOOLONG; 148 disk_link->len = min_t(unsigned int, 149 sizeof(struct fscrypt_symlink_data) + 150 fscrypt_fname_encrypted_size(dir, len), 151 max_len); 152 disk_link->name = NULL; 153 return 0; 154 } 155 EXPORT_SYMBOL_GPL(__fscrypt_prepare_symlink); 156 157 int __fscrypt_encrypt_symlink(struct inode *inode, const char *target, 158 unsigned int len, struct fscrypt_str *disk_link) 159 { 160 int err; 161 struct qstr iname = { .name = target, .len = len }; 162 struct fscrypt_symlink_data *sd; 163 unsigned int ciphertext_len; 164 struct fscrypt_str oname; 165 166 err = fscrypt_require_key(inode); 167 if (err) 168 return err; 169 170 if (disk_link->name) { 171 /* filesystem-provided buffer */ 172 sd = (struct fscrypt_symlink_data *)disk_link->name; 173 } else { 174 sd = kmalloc(disk_link->len, GFP_NOFS); 175 if (!sd) 176 return -ENOMEM; 177 } 178 ciphertext_len = disk_link->len - sizeof(*sd); 179 sd->len = cpu_to_le16(ciphertext_len); 180 181 oname.name = sd->encrypted_path; 182 oname.len = ciphertext_len; 183 err = fname_encrypt(inode, &iname, &oname); 184 if (err) { 185 if (!disk_link->name) 186 kfree(sd); 187 return err; 188 } 189 BUG_ON(oname.len != ciphertext_len); 190 191 /* 192 * Null-terminating the ciphertext doesn't make sense, but we still 193 * count the null terminator in the length, so we might as well 194 * initialize it just in case the filesystem writes it out. 195 */ 196 sd->encrypted_path[ciphertext_len] = '\0'; 197 198 if (!disk_link->name) 199 disk_link->name = (unsigned char *)sd; 200 return 0; 201 } 202 EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink); 203