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: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/crypto/keyinfo.c b/fs/crypto/keyinfo.c
index 06f5aa4..1ac263e 100644 (file)
--- a/fs/crypto/keyinfo.c
+++ b/fs/crypto/keyinfo.c
@@ -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)) {

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index ccf8bf4..dbd277e 100644 (file)
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -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 */

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 8a28f79..28c8992 100644 (file)
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -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
 }
 
 /*

diff --git a/include/linux/fscrypto.h b/include/linux/fscrypto.h
index 6027f6b..cfa6cde 100644 (file)
--- a/include/linux/fscrypto.h
+++ b/include/linux/fscrypto.h
@@ -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 *);