Fix PSA AEAD GCM's update output buffer length verification.

Move GCM's update output buffer length verification
from PSA AEAD to the built-in implementation of the GCM.

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

ChangeLog.d/psa_gcm_buffer_limitation.txt

@@ -3,6 +3,11 @@ Bugfix
      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.
+   * Move GCM's update output buffer length verification from PSA AEAD to
+     the built-in implementation of the GCM.
+     The requirement for output buffer size to be equal or greater then
+     input buffer size is valid only for the built-in implementation of GCM.
+     Alternative GCM implementations can process whole blocks only.
 
 API changes
    * New error code for GCM: MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL.

library/gcm.c

@@ -431,7 +431,7 @@ int mbedtls_gcm_update( mbedtls_gcm_context *ctx,
     unsigned char ectr[16];
 
     if( output_size < input_length )
-        return( MBEDTLS_ERR_GCM_BAD_INPUT );
+        return( MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL );
     GCM_VALIDATE_RET( output_length != NULL );
     *output_length = input_length;
 

library/psa_crypto_aead.c

@@ -510,9 +510,6 @@ psa_status_t mbedtls_psa_aead_update(
 #if defined(MBEDTLS_PSA_BUILTIN_ALG_GCM)
     if( operation->alg == PSA_ALG_GCM )
     {
-        if( output_size < input_length )
-            return( PSA_ERROR_BUFFER_TOO_SMALL );
-
         status =  mbedtls_to_psa_error(
             mbedtls_gcm_update( &operation->ctx.gcm,
                                 input, input_length,

tests/suites/test_suite_gcm.aes128_de.data

@@ -726,6 +726,10 @@ AES-GCM Bad IV (AES-128,128,0,0,32) #0
 depends_on:MBEDTLS_AES_C
 gcm_bad_parameters:MBEDTLS_CIPHER_ID_AES:MBEDTLS_GCM_DECRYPT:"d0194b6ee68f0ed8adc4b22ed15dbf14":"":"":"":32:MBEDTLS_ERR_GCM_BAD_INPUT
 
+AES-GCM, output buffer too small, NIST Validation (AES-128,128,1024,0,128) #0
+depends_on:MBEDTLS_AES_C
+gcm_update_output_buffer_too_small:MBEDTLS_CIPHER_ID_AES:MBEDTLS_GCM_DECRYPT:"0dd358bc3f992f26e81e3a2f3aa2d517":"87cc4fd75788c9d5cc83bae5d764dd249d178ab23224049795d4288b5ed9ea3f317068a39a7574b300c8544226e87b08e008fbe241d094545c211d56ac44437d41491a438272738968c8d371aa7787b5f606c8549a9d868d8a71380e9657d3c0337979feb01de5991fc1470dfc59eb02511efbbff3fcb479a862ba3844a25aaa":"d8c750bb443ee1a169dfe97cfe4d855b"
+
 AES-GCM Selftest
 depends_on:MBEDTLS_AES_C
 gcm_selftest:

tests/suites/test_suite_gcm.aes128_en.data

@@ -726,6 +726,9 @@ AES-GCM Bad IV (AES-128,128,0,0,32) #0
 depends_on:MBEDTLS_AES_C
 gcm_bad_parameters:MBEDTLS_CIPHER_ID_AES:MBEDTLS_GCM_ENCRYPT:"d0194b6ee68f0ed8adc4b22ed15dbf14":"":"":"":32:MBEDTLS_ERR_GCM_BAD_INPUT
 
+AES-GCM, output buffer too small, NIST Validation (AES-128,128,1024,0,128) #0
+gcm_update_output_buffer_too_small:MBEDTLS_CIPHER_ID_AES:MBEDTLS_GCM_ENCRYPT:"ce0f8cfe9d64c4f4c045d11b97c2d918":"dfff250d380f363880963b42d6913c1ba11e8edf7c4ab8b76d79ccbaac628f548ee542f48728a9a2620a0d69339c8291e8d398440d740e310908cdee7c273cc91275ce7271ba12f69237998b07b789b3993aaac8dc4ec1914432a30f5172f79ea0539bd1f70b36d437e5170bc63039a5280816c05e1e41760b58e35696cebd55":"ad4c3627a494fc628316dc03faf81db8"
+
 AES-GCM Selftest
 depends_on:MBEDTLS_AES_C
 gcm_selftest:

tests/suites/test_suite_gcm.function

@@ -431,6 +431,30 @@ exit:
 }
 /* END_CASE */
 
+/* BEGIN_CASE */
+void gcm_update_output_buffer_too_small( int cipher_id, int mode,
+                                         data_t * key_str, const data_t *input,
+                                         const data_t *iv )
+{
+    mbedtls_gcm_context ctx;
+    uint8_t *output = NULL;
+    size_t olen;
+    size_t output_len = input->len - 1;
+
+    mbedtls_gcm_init( &ctx );
+    TEST_EQUAL( mbedtls_gcm_setkey( &ctx, cipher_id, key_str->x, key_str->len * 8 ), 0 );
+    TEST_EQUAL( 0, mbedtls_gcm_starts( &ctx, mode, iv->x, iv->len ) );
+
+    ASSERT_ALLOC( output, output_len );
+    olen = 0xdeadbeef;
+    TEST_EQUAL( MBEDTLS_ERR_GCM_BUFFER_TOO_SMALL, mbedtls_gcm_update( &ctx, input->x, input->len, output, output_len, &olen ) );
+
+exit:
+    mbedtls_free( output );
+    mbedtls_gcm_free( &ctx );
+}
+/* END_CASE */
+
 /* BEGIN_CASE depends_on:MBEDTLS_SELF_TEST */
 void gcm_selftest(  )
 {