cryptsetup: do not assert when unsealing token without salt

Salt was added in v253. We are not checking whether it was actually found
(non-zero size), so when an old tpm+pin enrollment is opened things go boom.
For good measure, check both the buffer and the size in both places.

Assertion 'saltlen > 0' failed at src/shared/tpm2-util.c:2490, function tpm2_util_pbkdf2_hmac_sha256(). Aborting.

2 files changed, 5 insertions, 2 deletions

diff --git a/src/cryptsetup/cryptsetup-tokens/luks2-tpm2.c b/src/cryptsetup/cryptsetup-tokens/luks2-tpm2.c
index 80a2c0d316..c4377230ca 100644
--- a/src/cryptsetup/cryptsetup-tokens/luks2-tpm2.c
+++ b/src/cryptsetup/cryptsetup-tokens/luks2-tpm2.c
@@ -38,6 +38,7 @@ int acquire_luks2_key(
         _cleanup_(erase_and_freep) char *b64_salted_pin = NULL;
         int r;
 
+        assert(salt || salt_size == 0);
         assert(ret_decrypted_key);
         assert(ret_decrypted_key_size);
 
@@ -58,7 +59,7 @@ int acquire_luks2_key(
         if ((flags & TPM2_FLAGS_USE_PIN) && salt && !pin)
                 return -ENOANO;
 
-        if (pin) {
+        if (pin && salt_size > 0) {
                 uint8_t salted_pin[SHA256_DIGEST_SIZE] = {};
                 CLEANUP_ERASE(salted_pin);
                 r = tpm2_util_pbkdf2_hmac_sha256(pin, strlen(pin), salt, salt_size, salted_pin);
diff --git a/src/cryptsetup/cryptsetup-tpm2.c b/src/cryptsetup/cryptsetup-tpm2.c
index 2a8a38c593..a375a22758 100644
--- a/src/cryptsetup/cryptsetup-tpm2.c
+++ b/src/cryptsetup/cryptsetup-tpm2.c
@@ -86,6 +86,8 @@ int acquire_tpm2_key(
         const void *blob;
         int r;
 
+        assert(salt || salt_size == 0);
+
         if (!device) {
                 r = tpm2_find_device_auto(LOG_DEBUG, &auto_device);
                 if (r == -ENODEV)
@@ -152,7 +154,7 @@ int acquire_tpm2_key(
                 if (r < 0)
                         return r;
 
-                if (salt) {
+                if (salt_size > 0) {
                         uint8_t salted_pin[SHA256_DIGEST_SIZE] = {};
                         CLEANUP_ERASE(salted_pin);