EVP_PKEY_get_utf8_string_param(): ensure the string is NUL terminated

A check is added to fail this function if the string buffer isn't
large enough to accomodate a terminating NUL byte.

Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16334)

crypto/evp/p_lib.c

@@ -2145,7 +2145,7 @@ err:
 
 int EVP_PKEY_get_octet_string_param(const EVP_PKEY *pkey, const char *key_name,
                                     unsigned char *buf, size_t max_buf_sz,
-                                    size_t *out_sz)
+                                    size_t *out_len)
 {
     OSSL_PARAM params[2];
     int ret1 = 0, ret2 = 0;
@@ -2157,14 +2157,14 @@ int EVP_PKEY_get_octet_string_param(const EVP_PKEY *pkey, const char *key_name,
     params[1] = OSSL_PARAM_construct_end();
     if ((ret1 = EVP_PKEY_get_params(pkey, params)))
         ret2 = OSSL_PARAM_modified(params);
-    if (ret2 && out_sz != NULL)
-        *out_sz = params[0].return_size;
+    if (ret2 && out_len != NULL)
+        *out_len = params[0].return_size;
     return ret1 && ret2;
 }
 
 int EVP_PKEY_get_utf8_string_param(const EVP_PKEY *pkey, const char *key_name,
                                     char *str, size_t max_buf_sz,
-                                    size_t *out_sz)
+                                    size_t *out_len)
 {
     OSSL_PARAM params[2];
     int ret1 = 0, ret2 = 0;
@@ -2176,8 +2176,16 @@ int EVP_PKEY_get_utf8_string_param(const EVP_PKEY *pkey, const char *key_name,
     params[1] = OSSL_PARAM_construct_end();
     if ((ret1 = EVP_PKEY_get_params(pkey, params)))
         ret2 = OSSL_PARAM_modified(params);
-    if (ret2 && out_sz != NULL)
-        *out_sz = params[0].return_size;
+    if (ret2 && out_len != NULL)
+        *out_len = params[0].return_size;
+
+    if (ret2 && params[0].return_size == max_buf_sz)
+        /* There was no space for a NUL byte */
+        return 0;
+    /* Add a terminating NUL byte for good measure */
+    if (ret2 && str != NULL)
+        str[params[0].return_size] = '\0';
+
     return ret1 && ret2;
 }
 

doc/man3/EVP_PKEY_gettable_params.pod

@@ -47,14 +47,16 @@ EVP_PKEY_get_bn_param() retrieves a key I<pkey> BIGNUM value I<**bn>
 associated with a name of I<key_name>. If I<*bn> is NULL then the BIGNUM
 is allocated by the method.
 
-EVP_PKEY_get_utf8_string_param() get a key I<pkey> UTF8 string value int a buffer
-I<str> of maximum size I<max_buf_sz> associated with a name of I<key_name>.
-If I<out_sz> is not NULL the I<*out_sz> is set to the length of the string
+EVP_PKEY_get_utf8_string_param() get a key I<pkey> UTF8 string value into a
+buffer I<str> of maximum size I<max_buf_sz> associated with a name of
+I<key_name>.  The maximum size must be large enough to accomodate the string
+value including a terminating NUL byte, or this function will fail.
+If I<out_len> is not NULL, I<*out_len> is set to the length of the string
 not including the terminating NUL byte.
 
-EVP_PKEY_get_octet_string_param() copy a I<pkey>'s octet string value into a buffer
-I<buf> of maximum size I<max_buf_sz> associated with a name of I<key_name>.
-I<*out_sz> is the returned size of the buffer if it is not NULL.
+EVP_PKEY_get_octet_string_param() get a key I<pkey>'s octet string value into a
+buffer I<buf> of maximum size I<max_buf_sz> associated with a name of I<key_name>.
+If I<out_len> is not NULL, I<*out_len> is set to the length of the contents.
 
 =head1 NOTES