On Mon Jan 24, 2011 at 05:44:53PM +0100, Roberto Sassu <roberto.sassu@xxxxxxxxx> wrote: > The 'encrypted' key type defines its own payload format which contains a > symmetric key randomly generated that cannot be used directly to mount > an eCryptfs filesystem, because it expects an authentication token > structure. > > This patch introduces the new format 'ecryptfs' that allows to store an > authentication token structure inside the encrypted key payload containing > a randomly generated symmetric key, as the same for the format 'default'. > > More details about the usage of encrypted keys with the eCryptfs > filesystem can be found in the file 'Documentation/keys-ecryptfs.txt'. > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxx> > Acked-by: Gianluca Ramunno <ramunno@xxxxxxxxx> Reviewed-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxx> > --- > Documentation/keys-ecryptfs.txt | 68 +++++++++++++++++++++++++ > Documentation/keys-trusted-encrypted.txt | 6 ++- > security/keys/Makefile | 2 +- > security/keys/encrypted.c | 75 +++++++++++++++++++++++++--- > security/keys/keys_ecryptfs.c | 81 ++++++++++++++++++++++++++++++ > security/keys/keys_ecryptfs.h | 30 +++++++++++ > 6 files changed, 252 insertions(+), 10 deletions(-) > create mode 100644 Documentation/keys-ecryptfs.txt > create mode 100644 security/keys/keys_ecryptfs.c > create mode 100644 security/keys/keys_ecryptfs.h > > diff --git a/Documentation/keys-ecryptfs.txt b/Documentation/keys-ecryptfs.txt > new file mode 100644 > index 0000000..c3bbeba > --- /dev/null > +++ b/Documentation/keys-ecryptfs.txt > @@ -0,0 +1,68 @@ > + Encrypted keys for the eCryptfs filesystem > + > +ECryptfs is a stacked filesystem which transparently encrypts and decrypts each > +file using a randomly generated File Encryption Key (FEK). > + > +Each FEK is in turn encrypted with a File Encryption Key Encryption Key (FEFEK) > +either in kernel space or in user space with a daemon called 'ecryptfsd'. In > +the former case the operation is performed directly by the kernel CryptoAPI > +using a key, the FEFEK, derived from a user prompted passphrase; in the latter > +the FEK is encrypted by 'ecryptfsd' with the help of external libraries in order > +to support other mechanisms like public key cryptography, PKCS#11 and TPM based > +operations. > + > +The data structure defined by eCryptfs to contain information required for the > +FEK decryption is called authentication token and, currently, can be stored in a > +kernel key of the 'user' type, inserted in the user's session specific keyring > +by the userspace utility 'mount.ecryptfs' shipped with the package > +'ecryptfs-utils'. > + > +The 'encrypted' key type has been extended with the introduction of the new > +format 'ecryptfs' in order to be used in conjunction with the eCryptfs > +filesystem. Encrypted keys of the newly introduced format store an > +authentication token in its payload with a FEFEK randomly generated by the > +kernel and protected by the parent master key. > + > +In order to avoid known-plaintext attacks, the datablob obtained through > +commands 'keyctl print' or 'keyctl pipe' does not contain the overall > +authentication token, which content is well known, but only the FEFEK in > +encrypted form. > + > +The eCryptfs filesystem may really benefit from using encrypted keys in that the > +required key can be securely generated by an Administrator and provided at boot > +time after the unsealing of a 'trusted' key in order to perform the mount in a > +controlled environment. Another advantage is that the key is not exposed to > +threats of malicious software, because it is available in clear form only at > +kernel level. > + > +Usage: > + keyctl add encrypted name "new ecryptfs key-type:master-key-name keylen" ring > + keyctl add encrypted name "load hex_blob" ring > + keyctl update keyid "update key-type:master-key-name" > + > +name:= '<16 hexadecimal characters>' > +key-type:= 'trusted' | 'user' > +keylen:= 64 > + > + > +Example of encrypted key usage with the eCryptfs filesystem: > + > +Create an encrypted key "1000100010001000" of length 64 bytes with format > +'ecryptfs' and save it using a previously loaded user key "test": > + > + $ keyctl add encrypted 1000100010001000 "new ecryptfs user:test 64" @u > + 19184530 > + > + $ keyctl print 19184530 > + ecryptfs user:test 64 490045d4bfe48c99f0d465fbbbb79e7500da954178e2de0697 > + dd85091f5450a0511219e9f7cd70dcd498038181466f78ac8d4c19504fcc72402bfc41c2 > + f253a41b7507ccaa4b2b03fff19a69d1cc0b16e71746473f023a95488b6edfd86f7fdd40 > + 9d292e4bacded1258880122dd553a661 > + > + $ keyctl pipe 19184530 > ecryptfs.blob > + > +Mount an eCryptfs filesystem using the created encrypted key "1000100010001000" > +into the '/secret' directory: > + > + $ mount -i -t ecryptfs -oecryptfs_sig=1000100010001000,\ > + ecryptfs_cipher=aes,ecryptfs_key_bytes=32 /secret /secret > diff --git a/Documentation/keys-trusted-encrypted.txt b/Documentation/keys-trusted-encrypted.txt > index 0afcb50..5f50cca 100644 > --- a/Documentation/keys-trusted-encrypted.txt > +++ b/Documentation/keys-trusted-encrypted.txt > @@ -63,7 +63,7 @@ Usage: > keyctl add encrypted name "load hex_blob" ring > keyctl update keyid "update key-type:master-key-name" > > -format:= 'default' > +format:= 'default | ecryptfs' > key-type:= 'trusted' | 'user' > > > @@ -154,4 +154,6 @@ Load an encrypted key "evm" from saved blob: > 24717c64 5972dcb82ab2dde83376d82b2e3c09ffc > > Other uses for trusted and encrypted keys, such as for disk and file encryption > -are anticipated. > +are anticipated. In particular the new format 'ecryptfs' has been defined in > +in order to use encrypted keys to mount an eCryptfs filesystem. More details > +about the usage can be found in the file 'Documentation/keys-ecryptfs.txt'. > diff --git a/security/keys/Makefile b/security/keys/Makefile > index 1bf090a..bf8c878 100644 > --- a/security/keys/Makefile > +++ b/security/keys/Makefile > @@ -14,7 +14,7 @@ obj-y := \ > user_defined.o > > obj-$(CONFIG_TRUSTED_KEYS) += trusted.o > -obj-$(CONFIG_ENCRYPTED_KEYS) += encrypted.o > +obj-$(CONFIG_ENCRYPTED_KEYS) += keys_ecryptfs.o encrypted.o > obj-$(CONFIG_KEYS_COMPAT) += compat.o > obj-$(CONFIG_PROC_FS) += proc.o > obj-$(CONFIG_SYSCTL) += sysctl.o > diff --git a/security/keys/encrypted.c b/security/keys/encrypted.c > index 59f719e..a916ce2 100644 > --- a/security/keys/encrypted.c > +++ b/security/keys/encrypted.c > @@ -29,11 +29,13 @@ > #include <linux/rcupdate.h> > #include <linux/scatterlist.h> > #include <linux/crypto.h> > +#include <linux/ctype.h> > #include <crypto/hash.h> > #include <crypto/sha.h> > #include <crypto/aes.h> > > #include "encrypted.h" > +#include "keys_ecryptfs.h" > > static const char KEY_TRUSTED_PREFIX[] = "trusted:"; > static const char KEY_USER_PREFIX[] = "user:"; > @@ -41,11 +43,13 @@ static const char hash_alg[] = "sha256"; > static const char hmac_alg[] = "hmac(sha256)"; > static const char blkcipher_alg[] = "cbc(aes)"; > static const char key_format_default[] = "default"; > +static const char key_format_ecryptfs[] = "ecryptfs"; > static unsigned int ivsize; > static int blksize; > > #define KEY_TRUSTED_PREFIX_LEN (sizeof (KEY_TRUSTED_PREFIX) - 1) > #define KEY_USER_PREFIX_LEN (sizeof (KEY_USER_PREFIX) - 1) > +#define KEY_ECRYPTFS_DESC_LEN 16 > #define HASH_SIZE SHA256_DIGEST_SIZE > #define MAX_DATA_SIZE 4096 > #define MIN_DATA_SIZE 20 > @@ -63,11 +67,12 @@ enum { > }; > > enum { > - Opt_error = -1, Opt_default > + Opt_error = -1, Opt_default, Opt_ecryptfs > }; > > static const match_table_t key_format_tokens = { > {Opt_default, "default"}, > + {Opt_ecryptfs, "ecryptfs"}, > {Opt_error, NULL} > }; > > @@ -95,6 +100,34 @@ static int aes_get_sizes(void) > } > > /* > + * valid_ecryptfs_desc - verify the description of a new/loaded encrypted key > + * > + * The description of a encrypted key with format 'ecryptfs' must contain > + * exactly 16 hexadecimal characters. > + * > + */ > +static int valid_ecryptfs_desc(const char *ecryptfs_desc) > +{ > + int i; > + > + if (strlen(ecryptfs_desc) != KEY_ECRYPTFS_DESC_LEN) { > + pr_err("encrypted_key: key description must be %d hexadecimal " > + "characters long\n", KEY_ECRYPTFS_DESC_LEN); > + return -EINVAL; > + } > + > + for (i = 0; i < KEY_ECRYPTFS_DESC_LEN; i++) { > + if (!isxdigit(ecryptfs_desc[i])) { > + pr_err("encrypted_key: key description must contain " > + "only hexadecimal characters\n"); > + return -EINVAL; > + } > + } > + > + return 0; > +} > + > +/* > * valid_master_desc - verify the 'key-type:desc' of a new/updated master-key > * > * key-type:= "trusted:" | "user:" > @@ -158,7 +191,7 @@ static int datablob_parse(char *datablob, const char **format, > } > key_cmd = match_token(keyword, key_tokens, args); > > - /* Get optional format: default */ > + /* Get optional format: default | ecryptfs */ > p = strsep(&datablob, " \t"); > if (!p) { > pr_err("encrypted_key: insufficient parameters specified\n"); > @@ -167,6 +200,7 @@ static int datablob_parse(char *datablob, const char **format, > > key_format = match_token(p, key_format_tokens, args); > switch (key_format) { > + case Opt_ecryptfs: > case Opt_default: > *format = p; > *master_desc = strsep(&datablob, " \t"); > @@ -598,6 +632,17 @@ static struct encrypted_key_payload *encrypted_key_alloc(struct key *key, > format_len = (!format) ? strlen(key_format_default) : strlen(format); > decrypted_datalen = dlen; > payload_datalen = decrypted_datalen; > + if (format && !strcmp(format, key_format_ecryptfs)) { > + if (dlen != ECRYPTFS_MAX_KEY_BYTES) { > + pr_err("encrypted_key: keylen for the ecryptfs format " > + "must be equal to %d bytes\n", > + ECRYPTFS_MAX_KEY_BYTES); > + return ERR_PTR(-EINVAL); > + } > + decrypted_datalen = ECRYPTFS_MAX_KEY_BYTES; > + payload_datalen = sizeof(struct ecryptfs_auth_tok); > + } > + > encrypted_datalen = roundup(decrypted_datalen, blksize); > > datablob_len = format_len + 1 + strlen(master_desc) + 1 > @@ -683,8 +728,14 @@ static void __ekey_init(struct encrypted_key_payload *epayload, > > if (!format) > memcpy(epayload->format, key_format_default, format_len); > - else > + else { > + if (!strcmp(format, key_format_ecryptfs)) > + epayload->decrypted_data = > + ecryptfs_get_auth_tok_key((struct ecryptfs_auth_tok *)epayload->payload_data); > + > memcpy(epayload->format, format, format_len); > + } > + > memcpy(epayload->master_desc, master_desc, strlen(master_desc)); > memcpy(epayload->datalen, datalen, strlen(datalen)); > } > @@ -696,11 +747,21 @@ static void __ekey_init(struct encrypted_key_payload *epayload, > * itself. For an old key, decrypt the hex encoded data. > */ > static int encrypted_init(struct encrypted_key_payload *epayload, > - const char *format, const char *master_desc, > - const char *datalen, const char *hex_encoded_iv) > + const char *key_desc, const char *format, > + const char *master_desc, const char *datalen, > + const char *hex_encoded_iv) > { > int ret = 0; > > + if (format && !strcmp(format, key_format_ecryptfs)) { > + ret = valid_ecryptfs_desc(key_desc); > + if (ret < 0) > + return ret; > + > + ecryptfs_fill_auth_tok((struct ecryptfs_auth_tok *)epayload->payload_data, > + key_desc); > + } > + > __ekey_init(epayload, format, master_desc, datalen); > if (!hex_encoded_iv) { > get_random_bytes(epayload->iv, ivsize); > @@ -750,8 +811,8 @@ static int encrypted_instantiate(struct key *key, const void *data, > ret = PTR_ERR(epayload); > goto out; > } > - ret = encrypted_init(epayload, format, master_desc, decrypted_datalen, > - hex_encoded_iv); > + ret = encrypted_init(epayload, key->description, format, master_desc, > + decrypted_datalen, hex_encoded_iv); > if (ret < 0) { > kfree(epayload); > goto out; > diff --git a/security/keys/keys_ecryptfs.c b/security/keys/keys_ecryptfs.c > new file mode 100644 > index 0000000..6144b91 > --- /dev/null > +++ b/security/keys/keys_ecryptfs.c > @@ -0,0 +1,81 @@ > +/* > + * keys_ecryptfs.c: helper functions for the encrypted key type > + * > + * Copyright (C) 2006 International Business Machines Corp. > + * Copyright (C) 2010 Politecnico di Torino, Italy > + * TORSEC group -- http://security.polito.it > + * > + * Authors: > + * Michael A. Halcrow <mahalcro@xxxxxxxxxx> > + * Tyler Hicks <tyhicks@xxxxxx> > + * Roberto Sassu <roberto.sassu@xxxxxxxxx> > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License as published by > + * the Free Software Foundation, version 2 of the License. > + */ > + > +#include <linux/module.h> > +#include "keys_ecryptfs.h" > + > +u8 *ecryptfs_get_auth_tok_key(struct ecryptfs_auth_tok *auth_tok) > +{ > + return auth_tok->token.password.session_key_encryption_key; > +} > +EXPORT_SYMBOL(ecryptfs_get_auth_tok_key); > + > +/* > + * ecryptfs_get_versions() > + * > + * Source code taken from the software 'ecryptfs-utils' version 83. > + * > + */ > +void ecryptfs_get_versions(int *major, int *minor, int *file_version) > +{ > + *major = ECRYPTFS_VERSION_MAJOR; > + *minor = ECRYPTFS_VERSION_MINOR; > + if (file_version) > + *file_version = ECRYPTFS_SUPPORTED_FILE_VERSION; > +} > +EXPORT_SYMBOL(ecryptfs_get_versions); > + > +/* > + * ecryptfs_fill_auth_tok - fill the ecryptfs_auth_tok structure > + * > + * Fill the ecryptfs_auth_tok structure with required ecryptfs data. > + * The source code is inspired to the original function generate_payload() > + * shipped with the software 'ecryptfs-utils' version 83. > + * > + */ > +int ecryptfs_fill_auth_tok(struct ecryptfs_auth_tok *auth_tok, > + const char *key_desc) > +{ > + int major, minor; > + > + ecryptfs_get_versions(&major, &minor, NULL); > + auth_tok->version = (((uint16_t)(major << 8) & 0xFF00) > + | ((uint16_t)minor & 0x00FF)); > + auth_tok->token_type = ECRYPTFS_PASSWORD; > + strncpy((char *)auth_tok->token.password.signature, key_desc, > + ECRYPTFS_PASSWORD_SIG_SIZE); > + auth_tok->token.password.session_key_encryption_key_bytes = > + ECRYPTFS_MAX_KEY_BYTES; > + /* > + * Removed auth_tok->token.password.salt and > + * auth_tok->token.password.session_key_encryption_key > + * initialization from the original code > + */ > + /* TODO: Make the hash parameterizable via policy */ > + auth_tok->token.password.flags |= > + ECRYPTFS_SESSION_KEY_ENCRYPTION_KEY_SET; > + /* The kernel code will encrypt the session key. */ > + auth_tok->session_key.encrypted_key[0] = 0; > + auth_tok->session_key.encrypted_key_size = 0; > + /* Default; subject to change by kernel eCryptfs */ > + auth_tok->token.password.hash_algo = PGP_DIGEST_ALGO_SHA512; > + auth_tok->token.password.flags &= ~(ECRYPTFS_PERSISTENT_PASSWORD); > + return 0; > +} > +EXPORT_SYMBOL(ecryptfs_fill_auth_tok); > + > +MODULE_LICENSE("GPL"); > diff --git a/security/keys/keys_ecryptfs.h b/security/keys/keys_ecryptfs.h > new file mode 100644 > index 0000000..87f77ca > --- /dev/null > +++ b/security/keys/keys_ecryptfs.h > @@ -0,0 +1,30 @@ > +/* > + * keys_ecryptfs.h: helper functions for the encrypted key type > + * > + * Copyright (C) 2006 International Business Machines Corp. > + * Copyright (C) 2010 Politecnico di Torino, Italy > + * TORSEC group -- http://security.polito.it > + * > + * Authors: > + * Michael A. Halcrow <mahalcro@xxxxxxxxxx> > + * Tyler Hicks <tyhicks@xxxxxx> > + * Roberto Sassu <roberto.sassu@xxxxxxxxx> > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License as published by > + * the Free Software Foundation, version 2 of the License. > + */ > + > +#ifndef __KEYS_ECRYPTFS_H > +#define __KEYS_ECRYPTFS_H > + > +#include <linux/ecryptfs.h> > + > +#define PGP_DIGEST_ALGO_SHA512 10 > + > +u8 *ecryptfs_get_auth_tok_key(struct ecryptfs_auth_tok *auth_tok); > +void ecryptfs_get_versions(int *major, int *minor, int *file_version); > +int ecryptfs_fill_auth_tok(struct ecryptfs_auth_tok *auth_tok, > + const char *key_desc); > + > +#endif /* __KEYS_ECRYPTFS_H */ > -- > 1.7.3.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html