Re: [PATCH] cmd_set_passphrase: initialize KDF parameters

[Hongbo Li]

On 2024/8/12 9:41, Kent Overstreet wrote:
On Sun, Aug 11, 2024 at 11:40:38PM GMT, Mae Kasza wrote:
From: mae <g...@badat.dev>

The set-passphrase command failed to derive the key for disks initially
formatted with --encrypted and --no_passphrase.

This happened because bch_sb_crypt_init only configures the KDF params
if a passphrase is specified.
This commit makes the command initialize the KDF with the same parameters
as bch_sb_crypt_init if the key wasn't encrypted before.

Signed-off-by: Mae Kasza <g...@badat.dev>

This looks good to me, but I'm in the middle of a 20 hour drive and not
feeling super confident to review crypto stuff tonight, so maybe someone
else can go over it too before I pull it in..

---
  c_src/cmd_key.c |  9 +++++++--
  c_src/crypto.c  | 13 ++++++++-----
  c_src/crypto.h  |  1 +
  3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/c_src/cmd_key.c b/c_src/cmd_key.c
index adb0ac8d..2da83758 100644
--- a/c_src/cmd_key.c
+++ b/c_src/cmd_key.c
@@ -104,7 +104,8 @@ 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");
  
@@ -116,9 +117,13 @@ int cmd_set_passphrase(int argc, char *argv[])
                die("Error getting current key");
  
  	char *new_passphrase = read_passphrase_twice("Enter new passphrase: ");
+       if (!bch2_key_is_encrypted(&crypt->key)) {
+               bch_crypt_default_kdf_init(crypt);
It works, but using bch_sb_crypt_init to reinitialize crypt may be 
better. In bch_sb_crypt_init, it has initialized the crypt and also 
cleaned new_passphrase.

Thanks
Hongbo

+       }
+
        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),
+       if (bch2_chacha_encrypt_key(&passphrase_key, __bch2_sb_key_nonce(sb),
                                    &new_key, sizeof(new_key)))
                die("error encrypting key");
        crypt->key = new_key;
diff --git a/c_src/crypto.c b/c_src/crypto.c
index 32671bd8..30ad92d4 100644
--- a/c_src/crypto.c
+++ b/c_src/crypto.c
@@ -180,11 +180,7 @@ void bch_sb_crypt_init(struct bch_sb *sb,
        get_random_bytes(&crypt->key.key, sizeof(crypt->key.key));
  
  	if (passphrase) {
-
-               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));
+               bch_crypt_default_kdf_init(crypt);
  
  		struct bch_key passphrase_key = derive_passphrase(crypt, passphrase);
  
@@ -199,3 +195,10 @@ void bch_sb_crypt_init(struct bch_sb *sb,
                memzero_explicit(&passphrase_key, sizeof(passphrase_key));
        }
  }
+
+void bch_crypt_default_kdf_init(struct bch_sb_field_crypt *crypt) {
+               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));
+}
diff --git a/c_src/crypto.h b/c_src/crypto.h
index baea6d86..846a8931 100644
--- a/c_src/crypto.h
+++ b/c_src/crypto.h
@@ -18,5 +18,6 @@ void bch2_passphrase_check(struct bch_sb *, const char *,
  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_default_kdf_init(struct bch_sb_field_crypt *);
  
  #endif /* _CRYPTO_H */
--
2.45.2