fscrypt-crypt-util: fix IV incrementing for --iv-ino-lblk-32
authorEric Biggers <ebiggers@google.com>
Thu, 1 Oct 2020 00:25:04 +0000 (17:25 -0700)
committerEryu Guan <guaneryu@gmail.com>
Sun, 11 Oct 2020 03:27:53 +0000 (11:27 +0800)
fscrypt-crypt-util treats the "block number" part of the IV as 64-bit
when incrementing it.  That's wrong for --iv-ino-lblk-32 and
--iv-ino-lblk-64, as in those cases the block number should be 32-bit.

Fix this by using the correct length for the block number.

For --iv-ino-lblk-64 this doesn't actually matter, since in that case
the block number starts at 0 and never exceeds UINT32_MAX.

But for --iv-ino-lblk-32, the hashed inode number gets added to the
original block number to produce the IV block number, which can later
wrap around from UINT32_MAX to 0.  As a result, this change fixes
generic/602, though since the wraparound case isn't specifically tested
currently, the chance of failure was extremely small.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Daeho Jeong <daeho43@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
src/fscrypt-crypt-util.c

index d9189346cbbce3594e93a493ddb3dd518513b5a6..5c065116e8fcad173cd79a17f8c54614877ebbf6 100644 (file)
@@ -1692,16 +1692,32 @@ static const struct fscrypt_cipher *find_fscrypt_cipher(const char *name)
        return NULL;
 }
 
-struct fscrypt_iv {
-       union {
-               __le64 block_num;
-               u8 bytes[32];
+union fscrypt_iv {
+       /* usual IV format */
+       struct {
+               /* logical block number within the file */
+               __le64 block_number;
+
+               /* per-file nonce; only set in DIRECT_KEY mode */
+               u8 nonce[FILE_NONCE_SIZE];
+       };
+       /* IV format for IV_INO_LBLK_* modes */
+       struct {
+               /*
+                * IV_INO_LBLK_64: logical block number within the file
+                * IV_INO_LBLK_32: hashed inode number + logical block number
+                *                 within the file, mod 2^32
+                */
+               __le32 block_number32;
+
+               /* IV_INO_LBLK_64: inode number */
+               __le32 inode_number;
        };
 };
 
 static void crypt_loop(const struct fscrypt_cipher *cipher, const u8 *key,
-                      struct fscrypt_iv *iv, bool decrypting,
-                      size_t block_size, size_t padding)
+                      union fscrypt_iv *iv, bool decrypting,
+                      size_t block_size, size_t padding, bool is_bnum_32bit)
 {
        u8 *buf = xmalloc(block_size);
        size_t res;
@@ -1718,13 +1734,18 @@ static void crypt_loop(const struct fscrypt_cipher *cipher, const u8 *key,
                memset(&buf[res], 0, crypt_len - res);
 
                if (decrypting)
-                       cipher->decrypt(key, iv->bytes, buf, buf, crypt_len);
+                       cipher->decrypt(key, (u8 *)iv, buf, buf, crypt_len);
                else
-                       cipher->encrypt(key, iv->bytes, buf, buf, crypt_len);
+                       cipher->encrypt(key, (u8 *)iv, buf, buf, crypt_len);
 
                full_write(STDOUT_FILENO, buf, crypt_len);
 
-               iv->block_num = cpu_to_le64(le64_to_cpu(iv->block_num) + 1);
+               if (is_bnum_32bit)
+                       iv->block_number32 = cpu_to_le32(
+                                       le32_to_cpu(iv->block_number32) + 1);
+               else
+                       iv->block_number = cpu_to_le64(
+                                       le64_to_cpu(iv->block_number) + 1);
        }
        free(buf);
 }
@@ -1806,7 +1827,7 @@ static u32 hash_inode_number(const struct key_and_iv_params *params)
  */
 static void get_key_and_iv(const struct key_and_iv_params *params,
                           u8 *real_key, size_t real_key_size,
-                          struct fscrypt_iv *iv)
+                          union fscrypt_iv *iv)
 {
        bool file_nonce_in_iv = false;
        struct aes_key aes_key;
@@ -1860,14 +1881,14 @@ static void get_key_and_iv(const struct key_and_iv_params *params,
                        info[infolen++] = params->mode_num;
                        memcpy(&info[infolen], params->fs_uuid, UUID_SIZE);
                        infolen += UUID_SIZE;
-                       put_unaligned_le32(params->inode_number, &iv->bytes[4]);
+                       iv->inode_number = cpu_to_le32(params->inode_number);
                } else if (params->iv_ino_lblk_32) {
                        info[infolen++] = HKDF_CONTEXT_IV_INO_LBLK_32_KEY;
                        info[infolen++] = params->mode_num;
                        memcpy(&info[infolen], params->fs_uuid, UUID_SIZE);
                        infolen += UUID_SIZE;
-                       put_unaligned_le32(hash_inode_number(params),
-                                          iv->bytes);
+                       iv->block_number32 =
+                               cpu_to_le32(hash_inode_number(params));
                } else if (params->mode_num != 0) {
                        info[infolen++] = HKDF_CONTEXT_DIRECT_KEY;
                        info[infolen++] = params->mode_num;
@@ -1888,7 +1909,7 @@ static void get_key_and_iv(const struct key_and_iv_params *params,
        }
 
        if (file_nonce_in_iv && params->file_nonce_specified)
-               memcpy(&iv->bytes[8], params->file_nonce, FILE_NONCE_SIZE);
+               memcpy(iv->nonce, params->file_nonce, FILE_NONCE_SIZE);
 }
 
 enum {
@@ -1928,7 +1949,7 @@ int main(int argc, char *argv[])
        size_t padding = 0;
        const struct fscrypt_cipher *cipher;
        u8 real_key[MAX_KEY_SIZE];
-       struct fscrypt_iv iv;
+       union fscrypt_iv iv;
        char *tmp;
        int c;
 
@@ -2025,6 +2046,7 @@ int main(int argc, char *argv[])
 
        get_key_and_iv(&params, real_key, cipher->keysize, &iv);
 
-       crypt_loop(cipher, real_key, &iv, decrypting, block_size, padding);
+       crypt_loop(cipher, real_key, &iv, decrypting, block_size, padding,
+                  params.iv_ino_lblk_64 || params.iv_ino_lblk_32);
        return 0;
 }