commit 159171b72ac7080c3692587565b19142ac9fd32f
author Gilles Peskine <Gilles.Peskine@arm.com> Wed Dec 19 17:03:28 2018 +0100
committer Gilles Peskine <Gilles.Peskine@arm.com> Wed Dec 19 17:03:28 2018 +0100
tree d90baf39198d4ac5371321f32483567550c7b694
parent 1f19fa6f62346d57d5dac41512cc107c8a7fc7fb

PK parse/write: support keylen=0 correctly

A 0-length buffer for the key is a legitimate edge case. Ensure that
it works, even with buf=NULL. Document the key and keylen parameters.

There are already test cases for parsing an empty buffer. A subsequent
commit will add tests for writing to an empty buffer.

library/pkparse.c

diff --git a/library/pkparse.c b/library/pkparse.c
index 7c14e34..127f9b8 100644
--- a/library/pkparse.c
+++ b/library/pkparse.c
@@ -1170,15 +1170,16 @@
 #endif
 
     PK_VALIDATE_RET( pk != NULL );
-    PK_VALIDATE_RET( key != NULL || keylen == 0 );
-    PK_VALIDATE_RET( pwd != NULL || pwdlen == 0 );
+    if( keylen == 0 )
+        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );
+    PK_VALIDATE_RET( key != NULL );
 
 #if defined(MBEDTLS_PEM_PARSE_C)
    mbedtls_pem_init( &pem );
 
 #if defined(MBEDTLS_RSA_C)
     /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
-    if( keylen == 0 || key[keylen - 1] != '\0' )
+    if( key[keylen - 1] != '\0' )
         ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
     else
         ret = mbedtls_pem_read_buffer( &pem,
@@ -1209,7 +1210,7 @@
 
 #if defined(MBEDTLS_ECP_C)
     /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
-    if( keylen == 0 || key[keylen - 1] != '\0' )
+    if( key[keylen - 1] != '\0' )
         ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
     else
         ret = mbedtls_pem_read_buffer( &pem,
@@ -1239,7 +1240,7 @@
 #endif /* MBEDTLS_ECP_C */
 
     /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
-    if( keylen == 0 || key[keylen - 1] != '\0' )
+    if( key[keylen - 1] != '\0' )
         ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
     else
         ret = mbedtls_pem_read_buffer( &pem,
@@ -1262,7 +1263,7 @@
 
 #if defined(MBEDTLS_PKCS12_C) || defined(MBEDTLS_PKCS5_C)
     /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
-    if( keylen == 0 || key[keylen - 1] != '\0' )
+    if( key[keylen - 1] != '\0' )
         ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
     else
         ret = mbedtls_pem_read_buffer( &pem,
@@ -1300,9 +1301,6 @@
     {
         unsigned char *key_copy;
 
-        if( keylen == 0 )
-            return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );
-
         if( ( key_copy = mbedtls_calloc( 1, keylen ) ) == NULL )
             return( MBEDTLS_ERR_PK_ALLOC_FAILED );
 
@@ -1387,13 +1385,15 @@
 #endif
 
     PK_VALIDATE_RET( ctx != NULL );
+    if( keylen == 0 )
+        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );
     PK_VALIDATE_RET( key != NULL || keylen == 0 );
 
 #if defined(MBEDTLS_PEM_PARSE_C)
     mbedtls_pem_init( &pem );
 #if defined(MBEDTLS_RSA_C)
     /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
-    if( keylen == 0 || key[keylen - 1] != '\0' )
+    if( key[keylen - 1] != '\0' )
         ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
     else
         ret = mbedtls_pem_read_buffer( &pem,
@@ -1424,7 +1424,7 @@
 #endif /* MBEDTLS_RSA_C */
 
     /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
-    if( keylen == 0 || key[keylen - 1] != '\0' )
+    if( key[keylen - 1] != '\0' )
         ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
     else
         ret = mbedtls_pem_read_buffer( &pem,