Commit b5a7aef1 authored by Jaegeuk Kim's avatar Jaegeuk Kim
Browse files

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



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: default avatarJaegeuk Kim <jaegeuk@kernel.org>
parent 09210c97

fs/crypto/keyinfo.c

+76 −44
Original line number Diff line number Diff line
@@ -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 = 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;

		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)

	} else if (res) {

		goto out;

	}

got_key:

	ctfm = crypto_alloc_skcipher(cipher_str, 0, 0);

	if (!ctfm || IS_ERR(ctfm)) {

fs/f2fs/f2fs.h

+8 −0
Original line number Diff line number Diff line
@@ -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 */

fs/f2fs/super.c

+13 −0
Original line number Diff line number Diff line
@@ -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

}



/*

include/linux/fscrypto.h

+1 −0
Original line number Diff line number Diff line
@@ -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 *);

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