cryptsetup: handle more gracefully if "keyslots" LUKS2 JSON header field is invalid

The field is not owned by us (even though is in our JSON objects) but by
the LUKS2 spec. Hence let's handle this a bit more gracefully: let's not
get confused by it, just warn and skip over it.

Fixes: #20847

1 files changed, 12 insertions, 5 deletions

diff --git a/src/cryptsetup/cryptsetup-tpm2.c b/src/cryptsetup/cryptsetup-tpm2.c
index 4d95dacca5..8757212969 100644
--- a/src/cryptsetup/cryptsetup-tpm2.c
+++ b/src/cryptsetup/cryptsetup-tpm2.c
@@ -93,6 +93,7 @@ int find_tpm2_auto_data(
         for (token = start_token; token < sym_crypt_token_max(CRYPT_LUKS2); token++) {
                 _cleanup_(json_variant_unrefp) JsonVariant *v = NULL;
                 JsonVariant *w, *e;
+                int ks;
 
                 r = cryptsetup_get_token_as_json(cd, token, "systemd-tpm2", &v);
                 if (IN_SET(r, -ENOENT, -EINVAL, -EMEDIUMTYPE))
@@ -100,6 +101,14 @@ int find_tpm2_auto_data(
                 if (r < 0)
                         return log_error_errno(r, "Failed to read JSON token data off disk: %m");
 
+                ks = cryptsetup_get_keyslot_from_token(v);
+                if (ks < 0) {
+                        /* Handle parsing errors of the keyslots field gracefully, since it's not 'owned' by
+                         * us, but by the LUKS2 spec */
+                        log_warning_errno(ks, "Failed to extract keyslot index from TPM2 JSON data token %i, skipping: %m", token);
+                        continue;
+                }
+
                 w = json_variant_by_key(v, "tpm2-pcrs");
                 if (!w || !json_variant_is_array(w))
                         return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
@@ -125,6 +134,9 @@ int find_tpm2_auto_data(
                     search_pcr_mask != pcr_mask) /* PCR mask doesn't match what is configured, ignore this entry */
                         continue;
 
+                assert(keyslot < 0);
+                keyslot = ks;
+
                 assert(pcr_bank == UINT16_MAX);
                 assert(primary_alg == TPM2_ALG_ECC);
 
@@ -184,11 +196,6 @@ int find_tpm2_auto_data(
                         return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
                                                "Invalid base64 data in 'tpm2-policy-hash' field.");
 
-                assert(keyslot < 0);
-                keyslot = cryptsetup_get_keyslot_from_token(v);
-                if (keyslot < 0)
-                        return log_error_errno(keyslot, "Failed to extract keyslot index from TPM2 JSON data: %m");
-
                 break;
         }