Re: [PATCH] Extract bch_crypt_update_passphrase function

[Mae Kasza]

On 8/14/24 04:21, Hongbo Li wrote:


On 2024/8/14 1:37, Mae Kasza wrote:
This also fixes a bug where the set-passphrase
command failed to derive the key for disks initially
formatted with --encrypted and --no_passphrase, due to
bch_sb_crypt_init not configuring the KDF params if
the passphrase wasn't specified during formatting.

Signed-off-by: Mae Kasza <g...@badat.dev>
---
  c_src/cmd_key.c | 26 ++++++++++----------------
  c_src/crypto.c  | 43 ++++++++++++++++++++++++++++++++-----------
  c_src/crypto.h  |  3 +++
  3 files changed, 45 insertions(+), 27 deletions(-)

diff --git a/c_src/cmd_key.c b/c_src/cmd_key.c
index adb0ac8d..ac8a94a8 100644
--- a/c_src/cmd_key.c
+++ b/c_src/cmd_key.c
@@ -104,24 +104,19 @@ int cmd_set_passphrase(int argc, char *argv[])
      if (IS_ERR(c))
          die("Error opening %s: %s", argv[1], 
bch2_err_str(PTR_ERR(c)));
  -    struct bch_sb_field_crypt *crypt = 
bch2_sb_field_get(c->disk_sb.sb, crypt);
+    struct bch_sb *sb = c->disk_sb.sb;
+    struct bch_sb_field_crypt *crypt = bch2_sb_field_get(sb, crypt);
      if (!crypt)
          die("Filesystem does not have encryption enabled");
  -    struct bch_encrypted_key new_key;
-    new_key.magic = BCH_KEY_MAGIC;
-
-    int ret = bch2_decrypt_sb_key(c, crypt, &new_key.key);
+    struct bch_key key;
+    int ret = bch2_decrypt_sb_key(c, crypt, &key);
      if (ret)
          die("Error getting current key");
        char *new_passphrase = read_passphrase_twice("Enter new 
passphrase: ");
-    struct bch_key passphrase_key = derive_passphrase(crypt, 
new_passphrase);
  -    if (bch2_chacha_encrypt_key(&passphrase_key, 
__bch2_sb_key_nonce(c->disk_sb.sb),
-                    &new_key, sizeof(new_key)))
-        die("error encrypting key");
-    crypt->key = new_key;
+    bch_crypt_update_passphrase(sb, crypt, &key, new_passphrase);
        bch2_revoke_key(c->disk_sb.sb);
      bch2_write_super(c);
@@ -142,18 +137,17 @@ int cmd_remove_passphrase(int argc, char *argv[])
      if (IS_ERR(c))
          die("Error opening %s: %s", argv[1], 
bch2_err_str(PTR_ERR(c)));
  -    struct bch_sb_field_crypt *crypt = 
bch2_sb_field_get(c->disk_sb.sb, crypt);
+    struct bch_sb *sb = c->disk_sb.sb;
+    struct bch_sb_field_crypt *crypt = bch2_sb_field_get(sb, crypt);
      if (!crypt)
          die("Filesystem does not have encryption enabled");
  -    struct bch_encrypted_key new_key;
-    new_key.magic = BCH_KEY_MAGIC;
-
-    int ret = bch2_decrypt_sb_key(c, crypt, &new_key.key);
+    struct bch_key key;
+    int ret = bch2_decrypt_sb_key(c, crypt, &key);
      if (ret)
          die("Error getting current key");
  -    crypt->key = new_key;
+    bch_crypt_update_passphrase(sb, crypt, &key, NULL);
        bch2_write_super(c);
      bch2_fs_stop(c);
diff --git a/c_src/crypto.c b/c_src/crypto.c
index 32671bd8..301dbebe 100644
--- a/c_src/crypto.c
+++ b/c_src/crypto.c
@@ -176,26 +176,47 @@ void bch_sb_crypt_init(struct bch_sb *sb,
                 struct bch_sb_field_crypt *crypt,
                 const char *passphrase)
  {
+    struct bch_key key;
+    get_random_bytes(&key, sizeof(key));
+
      crypt->key.magic = BCH_KEY_MAGIC;
-    get_random_bytes(&crypt->key.key, sizeof(crypt->key.key));
+    crypt->key.key = key;
  -    if (passphrase) {
+    bch_crypt_update_passphrase(sb, crypt, &key, passphrase);
+}
  +void bch_crypt_update_passphrase(
+            struct bch_sb *sb,
+            struct bch_sb_field_crypt *crypt,
+            struct bch_key *key,
+            const char *new_passphrase)
+{
+
+    struct bch_encrypted_key new_key;
+    new_key.magic = BCH_KEY_MAGIC;
+    new_key.key = *key;
+
+    if(!new_passphrase) {
+        crypt->key = new_key;
May be the helper like this is needed. But we could assign the 
crypt->key outside, which seems more reasonable according to the 
helper name. Just in my humble opinion.

Thanks,
Hongbo

We need to assign to crypt->key regardless, since it's what contains the 
key encrypted with passphrase, I don't really see why we would want to 
leave that up to the caller

Thanks,

Mae


+        return;
+    }
+
+    // If crypt already has an encrypted key reuse it's encryption 
params
+    if (!bch2_key_is_encrypted(&crypt->key)) {
          SET_BCH_CRYPT_KDF_TYPE(crypt, BCH_KDF_SCRYPT);
          SET_BCH_KDF_SCRYPT_N(crypt, ilog2(16384));
          SET_BCH_KDF_SCRYPT_R(crypt, ilog2(8));
          SET_BCH_KDF_SCRYPT_P(crypt, ilog2(16));
+    }
  -        struct bch_key passphrase_key = derive_passphrase(crypt, 
passphrase);
-
-        assert(!bch2_key_is_encrypted(&crypt->key));
+    struct bch_key passphrase_key = derive_passphrase(crypt, 
new_passphrase);
  -        if (bch2_chacha_encrypt_key(&passphrase_key, 
__bch2_sb_key_nonce(sb),
-                       &crypt->key, sizeof(crypt->key)))
-            die("error encrypting key");
+    if (bch2_chacha_encrypt_key(&passphrase_key, 
__bch2_sb_key_nonce(sb),
+                    &new_key, sizeof(new_key)))
+        die("error encrypting key");
  -        assert(bch2_key_is_encrypted(&crypt->key));
+    memzero_explicit(&passphrase_key, sizeof(passphrase_key));
  -        memzero_explicit(&passphrase_key, sizeof(passphrase_key));
-    }
+    crypt->key = new_key;
+    assert(bch2_key_is_encrypted(&crypt->key));
  }
diff --git a/c_src/crypto.h b/c_src/crypto.h
index baea6d86..cd3baac8 100644
--- a/c_src/crypto.h
+++ b/c_src/crypto.h
@@ -19,4 +19,7 @@ void bch2_add_key(struct bch_sb *, const char *, 
const char *, const char *);
  void bch_sb_crypt_init(struct bch_sb *sb, struct bch_sb_field_crypt *,
                 const char *);
  +void bch_crypt_update_passphrase(struct bch_sb *sb, struct 
bch_sb_field_crypt *crypt,
+            struct bch_key *key, const char *new_passphrase);
+
  #endif /* _CRYPTO_H */