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fscrypto/f2fs: allow fs-specific key prefix for fs encryption

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This patch allows fscrypto to handle a second key prefix given by filesystem.
The main reason is to provide backward compatibility, since previously f2fs
used "f2fs:" as a crypto prefix instead of "fscrypt:".
Later, ext4 should also provide key_prefix() to give "ext4:".

One concern decribed by Ted would be kinda double check overhead of prefixes.
In x86, for example, validate_user_key consumes 8 ms after boot-up, which turns
out derive_key_aes() consumed most of the time to load specific crypto module.
After such the cold miss, it shows almost zero latencies, which treats as a
negligible overhead.
Note that request_key() detects wrong prefix in prior to derive_key_aes() even.

Cc: Ted Tso <tytso@mit.edu>
Cc: stable@vger.kernel.org # v4.6
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Jaegeuk Kim 2016-05-04 22:05:01 -07:00
parent 09210c973a
commit b5a7aef1ef
4 changed files with 98 additions and 44 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

120
fs/crypto/keyinfo.c
View File

@ -78,6 +78,67 @@ out:
return res;
}
static int validate_user_key(struct fscrypt_info *crypt_info,
struct fscrypt_context *ctx, u8 *raw_key,
u8 *prefix, int prefix_size)
{
u8 *full_key_descriptor;
struct key *keyring_key;
struct fscrypt_key *master_key;
const struct user_key_payload *ukp;
int full_key_len = prefix_size + (FS_KEY_DESCRIPTOR_SIZE * 2) + 1;
int res;
full_key_descriptor = kmalloc(full_key_len, GFP_NOFS);
if (!full_key_descriptor)
return -ENOMEM;
memcpy(full_key_descriptor, prefix, prefix_size);
sprintf(full_key_descriptor + prefix_size,
"%*phN", FS_KEY_DESCRIPTOR_SIZE,
ctx->master_key_descriptor);
full_key_descriptor[full_key_len - 1] = '\0';
keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
kfree(full_key_descriptor);
if (IS_ERR(keyring_key))
return PTR_ERR(keyring_key);
if (keyring_key->type != &key_type_logon) {
printk_once(KERN_WARNING
"%s: key type must be logon\n", __func__);
res = -ENOKEY;
goto out;
}
down_read(&keyring_key->sem);
ukp = user_key_payload(keyring_key);
if (ukp->datalen != sizeof(struct fscrypt_key)) {
res = -EINVAL;
up_read(&keyring_key->sem);
goto out;
}
master_key = (struct fscrypt_key *)ukp->data;
BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
printk_once(KERN_WARNING
"%s: key size incorrect: %d\n",
__func__, master_key->size);
res = -ENOKEY;
up_read(&keyring_key->sem);
goto out;
}
res = derive_key_aes(ctx->nonce, master_key->raw, raw_key);
up_read(&keyring_key->sem);
if (res)
goto out;
crypt_info->ci_keyring_key = keyring_key;
return 0;
out:
key_put(keyring_key);
return res;
}
static void put_crypt_info(struct fscrypt_info *ci)
{
if (!ci)
@ -91,12 +152,7 @@ static void put_crypt_info(struct fscrypt_info *ci)
int get_crypt_info(struct inode *inode)
{
struct fscrypt_info *crypt_info;
u8 full_key_descriptor[FS_KEY_DESC_PREFIX_SIZE +
(FS_KEY_DESCRIPTOR_SIZE * 2) + 1];
struct key *keyring_key = NULL;
struct fscrypt_key *master_key;
struct fscrypt_context ctx;
const struct user_key_payload *ukp;
struct crypto_skcipher *ctfm;
const char *cipher_str;
u8 raw_key[FS_MAX_KEY_SIZE];
@ -167,48 +223,24 @@ retry:
memset(raw_key, 0x42, FS_AES_256_XTS_KEY_SIZE);
goto got_key;
}
memcpy(full_key_descriptor, FS_KEY_DESC_PREFIX,
FS_KEY_DESC_PREFIX_SIZE);
sprintf(full_key_descriptor + FS_KEY_DESC_PREFIX_SIZE,
"%*phN", FS_KEY_DESCRIPTOR_SIZE,
ctx.master_key_descriptor);
full_key_descriptor[FS_KEY_DESC_PREFIX_SIZE +
(2 * FS_KEY_DESCRIPTOR_SIZE)] = '\0';
keyring_key = request_key(&key_type_logon, full_key_descriptor, NULL);
if (IS_ERR(keyring_key)) {
res = PTR_ERR(keyring_key);
keyring_key = NULL;
goto out;
}
crypt_info->ci_keyring_key = keyring_key;
if (keyring_key->type != &key_type_logon) {
printk_once(KERN_WARNING
"%s: key type must be logon\n", __func__);
res = -ENOKEY;
goto out;
}
down_read(&keyring_key->sem);
ukp = user_key_payload(keyring_key);
if (ukp->datalen != sizeof(struct fscrypt_key)) {
res = -EINVAL;
up_read(&keyring_key->sem);
goto out;
}
master_key = (struct fscrypt_key *)ukp->data;
BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
if (master_key->size != FS_AES_256_XTS_KEY_SIZE) {
printk_once(KERN_WARNING
"%s: key size incorrect: %d\n",
__func__, master_key->size);
res = -ENOKEY;
up_read(&keyring_key->sem);
res = validate_user_key(crypt_info, &ctx, raw_key,
FS_KEY_DESC_PREFIX, FS_KEY_DESC_PREFIX_SIZE);
if (res && inode->i_sb->s_cop->key_prefix) {
u8 *prefix = NULL;
int prefix_size, res2;
prefix_size = inode->i_sb->s_cop->key_prefix(inode, &prefix);
res2 = validate_user_key(crypt_info, &ctx, raw_key,
prefix, prefix_size);
if (res2) {
if (res2 == -ENOKEY)
res = -ENOKEY;
goto out;
}
} else if (res) {
goto out;
}
res = derive_key_aes(ctx.nonce, master_key->raw, raw_key);
up_read(&keyring_key->sem);
if (res)
goto out;
got_key:
ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);
if (!ctfm || IS_ERR(ctfm)) {

8
fs/f2fs/f2fs.h
View File

@ -711,6 +711,10 @@ enum {
MAX_TIME,
};
#ifdef CONFIG_F2FS_FS_ENCRYPTION
#define F2FS_KEY_DESC_PREFIX "f2fs:"
#define F2FS_KEY_DESC_PREFIX_SIZE 5
#endif
struct f2fs_sb_info {
struct super_block *sb; /* pointer to VFS super block */
struct proc_dir_entry *s_proc; /* proc entry */
@ -718,6 +722,10 @@ struct f2fs_sb_info {
int valid_super_block; /* valid super block no */
int s_flag; /* flags for sbi */
#ifdef CONFIG_F2FS_FS_ENCRYPTION
u8 key_prefix[F2FS_KEY_DESC_PREFIX_SIZE];
u8 key_prefix_size;
#endif
/* for node-related operations */
struct f2fs_nm_info *nm_info; /* node manager */
struct inode *node_inode; /* cache node blocks */

13
fs/f2fs/super.c
View File

@ -964,6 +964,12 @@ static int f2fs_get_context(struct inode *inode, void *ctx, size_t len)
ctx, len, NULL);
}
static int f2fs_key_prefix(struct inode *inode, u8 **key)
{
*key = F2FS_I_SB(inode)->key_prefix;
return F2FS_I_SB(inode)->key_prefix_size;
}
static int f2fs_set_context(struct inode *inode, const void *ctx, size_t len,
void *fs_data)
{
@ -980,6 +986,7 @@ static unsigned f2fs_max_namelen(struct inode *inode)
static struct fscrypt_operations f2fs_cryptops = {
.get_context = f2fs_get_context,
.key_prefix = f2fs_key_prefix,
.set_context = f2fs_set_context,
.is_encrypted = f2fs_encrypted_inode,
.empty_dir = f2fs_empty_dir,
@ -1305,6 +1312,12 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
INIT_LIST_HEAD(&sbi->s_list);
mutex_init(&sbi->umount_mutex);
#ifdef CONFIG_F2FS_FS_ENCRYPTION
memcpy(sbi->key_prefix, F2FS_KEY_DESC_PREFIX,
F2FS_KEY_DESC_PREFIX_SIZE);
sbi->key_prefix_size = F2FS_KEY_DESC_PREFIX_SIZE;
#endif
}
/*

1
include/linux/fscrypto.h
View File

@ -175,6 +175,7 @@ struct fscrypt_name {
*/
struct fscrypt_operations {
int (*get_context)(struct inode *, void *, size_t);
int (*key_prefix)(struct inode *, u8 **);
int (*prepare_context)(struct inode *);
int (*set_context)(struct inode *, const void *, size_t, void *);
int (*dummy_context)(struct inode *);