commit f28261fc14da5f52b460c903e027aff187f9cf5f
author Mateusz Starzyk <mateusz.starzyk@mobica.com> Thu Sep 30 16:39:07 2021 +0200
committer Mateusz Starzyk <mateusz.starzyk@mobica.com> Mon Oct 04 13:54:54 2021 +0200
tree b9f6ca642121b4ab63f80e4e68ec6bd2be04d9a4
parent cd51e765830387a4aab8e24fb912b714464d42b8

Remove output buffer limitation for PSA with GCM.

The requirement of minimum 15 bytes for output buffer in
psa_aead_finish() and psa_aead_verify() does not apply
to the built-in implementation of the GCM.

Alternative implementations are expected to verify the
length of the provided output buffers and to return
the MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL in case the
buffer length is too small.

Signed-off-by: Mateusz Starzyk <mateusz.starzyk@mobica.com>

ChangeLog.d/psa_gcm_buffer_limitation.txt

diff --git a/ChangeLog.d/psa_gcm_buffer_limitation.txt b/ChangeLog.d/psa_gcm_buffer_limitation.txt
new file mode 100644
index 0000000..7259e50
--- /dev/null
+++ b/ChangeLog.d/psa_gcm_buffer_limitation.txt
@@ -0,0 +1,11 @@
+Bugfix
+   * Remove PSA'a AEAD finish/verify output buffer limitation for GCM.
+     The requirement of minimum 15 bytes for output buffer in
+     psa_aead_finish() and psa_aead_verify() does not apply to the built-in
+     implementation of GCM.
+
+API changes
+   * New error code for GCM: MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL.
+     Alternative GCM implementations are expected to verify
+     the length of the provided output buffers and to return the
+     MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL in case the buffer length is too small.

include/mbedtls/gcm.h

diff --git a/include/mbedtls/gcm.h b/include/mbedtls/gcm.h
index 9d9155f..a4de919 100644
--- a/include/mbedtls/gcm.h
+++ b/include/mbedtls/gcm.h
@@ -45,6 +45,8 @@
 #define MBEDTLS_ERR_GCM_AUTH_FAILED                       -0x0012
 /** Bad input parameters to function. */
 #define MBEDTLS_ERR_GCM_BAD_INPUT                         -0x0014
+/** An output buffer is too small. */
+#define MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL                  -0x0018
 
 #ifdef __cplusplus
 extern "C" {

library/psa_crypto.c

diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index ece64b1..5978b6a 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -201,6 +201,8 @@
 
         case MBEDTLS_ERR_GCM_AUTH_FAILED:
             return( PSA_ERROR_INVALID_SIGNATURE );
+        case MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL:
+            return( PSA_ERROR_BUFFER_TOO_SMALL );
         case MBEDTLS_ERR_GCM_BAD_INPUT:
             return( PSA_ERROR_INVALID_ARGUMENT );
 

library/psa_crypto_aead.c

diff --git a/library/psa_crypto_aead.c b/library/psa_crypto_aead.c
index a72865c..673cdf3 100644
--- a/library/psa_crypto_aead.c
+++ b/library/psa_crypto_aead.c
@@ -567,9 +567,6 @@
 #if defined(MBEDTLS_PSA_BUILTIN_ALG_GCM)
     if( operation->alg == PSA_ALG_GCM )
     {
-        if( ciphertext_size < 15 )
-            return( PSA_ERROR_BUFFER_TOO_SMALL );
-
         status =  mbedtls_to_psa_error(
             mbedtls_gcm_finish( &operation->ctx.gcm,
                                 ciphertext, ciphertext_size, ciphertext_length,

tests/suites/test_suite_psa_crypto.data

diff --git a/tests/suites/test_suite_psa_crypto.data b/tests/suites/test_suite_psa_crypto.data
index 063629e..3a3e678 100644
--- a/tests/suites/test_suite_psa_crypto.data
+++ b/tests/suites/test_suite_psa_crypto.data
@@ -3348,7 +3348,7 @@
 
 PSA AEAD finish buffer test: AES - GCM, BUF = 8, TAG = 16
 depends_on:PSA_WANT_ALG_GCM:PSA_WANT_KEY_TYPE_AES
-aead_multipart_finish_buffer_test:PSA_KEY_TYPE_AES:"fbc0b4c56a714c83217b2d1bcadd2ed2e9efb0dcac6cc19f":PSA_ALG_GCM:8:16:"5f4b43e811da9c470d6a9b01":"":"d2ae38c4375954835d75b8e4c2f9bbb4":PSA_ERROR_BUFFER_TOO_SMALL
+aead_multipart_finish_buffer_test:PSA_KEY_TYPE_AES:"fbc0b4c56a714c83217b2d1bcadd2ed2e9efb0dcac6cc19f":PSA_ALG_GCM:8:16:"5f4b43e811da9c470d6a9b01":"":"d2ae38c4375954835d75b8e4c2f9bbb4":PSA_SUCCESS
 
 PSA AEAD finish buffer test: AES - GCM, BUF = 15, TAG = 20
 depends_on:PSA_WANT_ALG_GCM:PSA_WANT_KEY_TYPE_AES