Merge pull request #3935 from paul-elliott-arm/fix_pem_write_2_16
Backport 2.16: Remove Extraneous bytes from buffer post pem write
diff --git a/ChangeLog.d/clean_pem_buffers.txt b/ChangeLog.d/clean_pem_buffers.txt
new file mode 100644
index 0000000..818fad9
--- /dev/null
+++ b/ChangeLog.d/clean_pem_buffers.txt
@@ -0,0 +1,6 @@
+Bugfix
+ * In PEM writing functions, fill the trailing part of the buffer with null
+ bytes. This guarantees that the corresponding parsing function can read
+ the buffer back, which was the case for mbedtls_x509write_{crt,csr}_pem
+ until this property was inadvertently broken in Mbed TLS 2.19.0.
+ Fixes #3682.
diff --git a/library/pem.c b/library/pem.c
index a7a2f7f..50e663c 100644
--- a/library/pem.c
+++ b/library/pem.c
@@ -508,8 +508,12 @@
*p++ = '\0';
*olen = p - buf;
+ /* Clean any remaining data previously written to the buffer */
+ memset( buf + *olen, 0, buf_len - *olen );
+
mbedtls_free( encode_buf );
return( 0 );
}
#endif /* MBEDTLS_PEM_WRITE_C */
#endif /* MBEDTLS_PEM_PARSE_C || MBEDTLS_PEM_WRITE_C */
+
diff --git a/tests/suites/test_suite_pkwrite.function b/tests/suites/test_suite_pkwrite.function
index 43c275e..2bad4ed 100644
--- a/tests/suites/test_suite_pkwrite.function
+++ b/tests/suites/test_suite_pkwrite.function
@@ -17,7 +17,7 @@
unsigned char check_buf[5000];
int ret;
FILE *f;
- size_t ilen;
+ size_t ilen, pem_len, buf_index;
memset( buf, 0, sizeof( buf ) );
memset( check_buf, 0, sizeof( check_buf ) );
@@ -28,12 +28,20 @@
ret = mbedtls_pk_write_pubkey_pem( &key, buf, sizeof( buf ));
TEST_ASSERT( ret == 0 );
+ pem_len = strlen( (char *) buf );
+
+ // check that the rest of the buffer remains clear
+ for( buf_index = pem_len; buf_index < sizeof( buf ); ++buf_index )
+ {
+ TEST_ASSERT( buf[buf_index] == 0 );
+ }
+
f = fopen( key_file, "r" );
TEST_ASSERT( f != NULL );
ilen = fread( check_buf, 1, sizeof( check_buf ), f );
fclose( f );
- TEST_ASSERT( ilen == strlen( (char *) buf ) );
+ TEST_ASSERT( ilen == pem_len );
TEST_ASSERT( memcmp( (char *) buf, (char *) check_buf, ilen ) == 0 );
exit:
@@ -49,7 +57,7 @@
unsigned char check_buf[5000];
int ret;
FILE *f;
- size_t ilen;
+ size_t ilen, pem_len, buf_index;
memset( buf, 0, sizeof( buf ) );
memset( check_buf, 0, sizeof( check_buf ) );
@@ -60,6 +68,14 @@
ret = mbedtls_pk_write_key_pem( &key, buf, sizeof( buf ));
TEST_ASSERT( ret == 0 );
+ pem_len = strlen( (char *) buf );
+
+ // check that the rest of the buffer remains clear
+ for( buf_index = pem_len; buf_index < sizeof( buf ); ++buf_index )
+ {
+ TEST_ASSERT( buf[buf_index] == 0 );
+ }
+
f = fopen( key_file, "r" );
TEST_ASSERT( f != NULL );
ilen = fread( check_buf, 1, sizeof( check_buf ), f );
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 535807e..40bccd6 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -45,7 +45,7 @@
unsigned char buf[4096];
unsigned char check_buf[4000];
int ret;
- size_t olen = 0, pem_len = 0;
+ size_t olen = 0, pem_len = 0, buf_index;
int der_len = -1;
FILE *f;
const char *subject_name = "C=NL,O=PolarSSL,CN=PolarSSL Server 1";
@@ -71,6 +71,11 @@
pem_len = strlen( (char *) buf );
+ for( buf_index = pem_len; buf_index < sizeof( buf ); ++buf_index )
+ {
+ TEST_ASSERT( buf[buf_index] == 0 );
+ }
+
f = fopen( cert_req_check_file, "r" );
TEST_ASSERT( f != NULL );
olen = fread( check_buf, 1, sizeof( check_buf ), f );
@@ -113,7 +118,7 @@
unsigned char check_buf[5000];
mbedtls_mpi serial;
int ret;
- size_t olen = 0, pem_len = 0;
+ size_t olen = 0, pem_len = 0, buf_index = 0;
int der_len = -1;
FILE *f;
rnd_pseudo_info rnd_info;
@@ -182,6 +187,12 @@
pem_len = strlen( (char *) buf );
+ // check that the rest of the buffer remains clear
+ for( buf_index = pem_len; buf_index < sizeof( buf ); ++buf_index )
+ {
+ TEST_ASSERT( buf[buf_index] == 0 );
+ }
+
f = fopen( cert_check_file, "r" );
TEST_ASSERT( f != NULL );
olen = fread( check_buf, 1, sizeof( check_buf ), f );
