json: replace JSON_FORMAT_REFUSE_SENSITIVE with JSON_FORMAT_CENSOR_SENSITIVE

Previously, the flag would completely refuse formatting a JSON object if
any field of it was marked sensitive. With this change we'll simply
replace the subobject with the string "<sensitive data>", and show
everything else.

This is tremendously useful when debugging, since it means that we can
again trace varlink calls through the stack: we can show all the message
metadata and just suppress the actually sensitive parameters.

The ability to debug this matters, and we should not hide more
information that we can get away with, to keep things debuggable and
maintainable.

4 files changed, 53 insertions, 40 deletions

diff --git a/src/shared/json.c b/src/shared/json.c
index 270aef4105..7ec6368e1e 100644
--- a/src/shared/json.c
+++ b/src/shared/json.c
@@ -1612,6 +1612,15 @@ static int json_format(FILE *f, JsonVariant *v, JsonFormatFlags flags, const cha
         assert(f);
         assert(v);
 
+        if (FLAGS_SET(flags, JSON_FORMAT_CENSOR_SENSITIVE) && json_variant_is_sensitive(v)) {
+                if (flags & JSON_FORMAT_COLOR)
+                        fputs(ansi_red(), f);
+                fputs("\"<sensitive data>\"", f);
+                if (flags & JSON_FORMAT_COLOR)
+                        fputs(ANSI_NORMAL, f);
+                return 0;
+        }
+
         switch (json_variant_type(v)) {
 
         case JSON_VARIANT_REAL: {
@@ -1818,10 +1827,6 @@ int json_variant_format(JsonVariant *v, JsonFormatFlags flags, char **ret) {
         if (flags & JSON_FORMAT_OFF)
                 return -ENOEXEC;
 
-        if ((flags & JSON_FORMAT_REFUSE_SENSITIVE))
-                if (json_variant_is_sensitive_recursive(v))
-                        return -EPERM;
-
         f = memstream_init(&m);
         if (!f)
                 return -ENOMEM;
diff --git a/src/shared/json.h b/src/shared/json.h
index 156f8e731e..9c8448f728 100644
--- a/src/shared/json.h
+++ b/src/shared/json.h
@@ -197,7 +197,7 @@ typedef enum JsonFormatFlags {
         JSON_FORMAT_FLUSH            = 1 << 8, /* call fflush() after dumping JSON */
         JSON_FORMAT_EMPTY_ARRAY      = 1 << 9, /* output "[]" for empty input */
         JSON_FORMAT_OFF              = 1 << 10, /* make json_variant_format() fail with -ENOEXEC */
-        JSON_FORMAT_REFUSE_SENSITIVE = 1 << 11, /* return EPERM if any node in the tree is marked as senstitive */
+        JSON_FORMAT_CENSOR_SENSITIVE = 1 << 11, /* Replace all sensitive elements with the string "<sensitive data>" */
 } JsonFormatFlags;
 
 int json_variant_format(JsonVariant *v, JsonFormatFlags flags, char **ret);
diff --git a/src/shared/varlink.c b/src/shared/varlink.c
index 96dfd8de92..7c37211cdd 100644
--- a/src/shared/varlink.c
+++ b/src/shared/varlink.c
@@ -1860,56 +1860,60 @@ Varlink* varlink_flush_close_unref(Varlink *v) {
 
 static int varlink_format_json(Varlink *v, JsonVariant *m) {
         _cleanup_(erase_and_freep) char *text = NULL;
-        bool sensitive = false;
-        int r;
+        int sz, r;
 
         assert(v);
         assert(m);
 
-        r = json_variant_format(m, JSON_FORMAT_REFUSE_SENSITIVE, &text);
-        if (r == -EPERM) {
-                sensitive = true;
-                r = json_variant_format(m, /* flags= */ 0, &text);
-        }
-        if (r < 0)
-                return r;
-        assert(text[r] == '\0');
+        sz = json_variant_format(m, /* flags= */ 0, &text);
+        if (sz < 0)
+                return sz;
+        assert(text[sz] == '\0');
 
-        if (v->output_buffer_size + r + 1 > VARLINK_BUFFER_MAX)
+        if (v->output_buffer_size + sz + 1 > VARLINK_BUFFER_MAX)
                 return -ENOBUFS;
 
-        varlink_log(v, "Sending message: %s", sensitive ? "<sensitive data>" : text);
+        if (DEBUG_LOGGING) {
+                _cleanup_(erase_and_freep) char *censored_text = NULL;
+
+                /* Suppress sensitive fields in the debug output */
+                r = json_variant_format(m, /* flags= */ JSON_FORMAT_CENSOR_SENSITIVE, &censored_text);
+                if (r < 0)
+                        return r;
+
+                varlink_log(v, "Sending message: %s", censored_text);
+        }
 
         if (v->output_buffer_size == 0) {
 
                 free_and_replace(v->output_buffer, text);
 
-                v->output_buffer_size = r + 1;
+                v->output_buffer_size = sz + 1;
                 v->output_buffer_index = 0;
 
         } else if (v->output_buffer_index == 0) {
 
-                if (!GREEDY_REALLOC(v->output_buffer, v->output_buffer_size + r + 1))
+                if (!GREEDY_REALLOC(v->output_buffer, v->output_buffer_size + sz + 1))
                         return -ENOMEM;
 
-                memcpy(v->output_buffer + v->output_buffer_size, text, r + 1);
-                v->output_buffer_size += r + 1;
+                memcpy(v->output_buffer + v->output_buffer_size, text, sz + 1);
+                v->output_buffer_size += sz + 1;
         } else {
                 char *n;
-                const size_t new_size = v->output_buffer_size + r + 1;
+                const size_t new_size = v->output_buffer_size + sz + 1;
 
                 n = new(char, new_size);
                 if (!n)
                         return -ENOMEM;
 
-                memcpy(mempcpy(n, v->output_buffer + v->output_buffer_index, v->output_buffer_size), text, r + 1);
+                memcpy(mempcpy(n, v->output_buffer + v->output_buffer_index, v->output_buffer_size), text, sz + 1);
 
                 free_and_replace(v->output_buffer, n);
                 v->output_buffer_size = new_size;
                 v->output_buffer_index = 0;
         }
 
-        if (sensitive)
+        if (json_variant_is_sensitive_recursive(m))
                 v->output_buffer_sensitive = true; /* Propagate sensitive flag */
         else
                 text = mfree(text); /* No point in the erase_and_free() destructor declared above */
diff --git a/src/test/test-json.c b/src/test/test-json.c
index 333fbe6cf2..cb0adc2643 100644
--- a/src/test/test-json.c
+++ b/src/test/test-json.c
@@ -107,9 +107,9 @@ static void test_variant_one(const char *data, Test test) {
         assert_se(json_variant_equal(v, w));
 
         s = mfree(s);
-        r = json_variant_format(w, JSON_FORMAT_REFUSE_SENSITIVE, &s);
-        assert_se(r == -EPERM);
-        assert_se(!s);
+        r = json_variant_format(w, JSON_FORMAT_CENSOR_SENSITIVE, &s);
+        assert_se(s);
+        assert_se(streq_ptr(s, "\"<sensitive data>\""));
 
         s = mfree(s);
         r = json_variant_format(w, JSON_FORMAT_PRETTY, &s);
@@ -886,10 +886,11 @@ TEST(json_sensitive) {
 
         json_variant_sensitive(a);
 
-        assert_se(json_variant_format(a, JSON_FORMAT_REFUSE_SENSITIVE, &s) == -EPERM);
-        assert_se(!s);
+        assert_se(json_variant_format(a, JSON_FORMAT_CENSOR_SENSITIVE, &s) >= 0);
+        assert_se(streq_ptr(s, "\"<sensitive data>\""));
+        s = mfree(s);
 
-        r = json_variant_format(b, JSON_FORMAT_REFUSE_SENSITIVE, &s);
+        r = json_variant_format(b, JSON_FORMAT_CENSOR_SENSITIVE, &s);
         assert_se(r >= 0);
         assert_se(s);
         assert_se((size_t) r == strlen(s));
@@ -901,7 +902,7 @@ TEST(json_sensitive) {
                                              JSON_BUILD_PAIR("e", JSON_BUILD_EMPTY_OBJECT))) >= 0);
         json_variant_dump(v, JSON_FORMAT_COLOR|JSON_FORMAT_PRETTY, NULL, NULL);
 
-        r = json_variant_format(v, JSON_FORMAT_REFUSE_SENSITIVE, &s);
+        r = json_variant_format(v, JSON_FORMAT_CENSOR_SENSITIVE, &s);
         assert_se(r >= 0);
         assert_se(s);
         assert_se((size_t) r == strlen(s));
@@ -915,7 +916,7 @@ TEST(json_sensitive) {
                                              JSON_BUILD_PAIR("e", JSON_BUILD_EMPTY_OBJECT))) >= 0);
         json_variant_dump(v, JSON_FORMAT_COLOR|JSON_FORMAT_PRETTY, NULL, NULL);
 
-        r = json_variant_format(v, JSON_FORMAT_REFUSE_SENSITIVE, &s);
+        r = json_variant_format(v, JSON_FORMAT_CENSOR_SENSITIVE, &s);
         assert_se(r >= 0);
         assert_se(s);
         assert_se((size_t) r == strlen(s));
@@ -930,8 +931,9 @@ TEST(json_sensitive) {
                                              JSON_BUILD_PAIR("e", JSON_BUILD_EMPTY_OBJECT))) >= 0);
         json_variant_dump(v, JSON_FORMAT_COLOR|JSON_FORMAT_PRETTY, NULL, NULL);
 
-        assert_se(json_variant_format(v, JSON_FORMAT_REFUSE_SENSITIVE, &s) == -EPERM);
-        assert_se(!s);
+        assert_se(json_variant_format(v, JSON_FORMAT_CENSOR_SENSITIVE, &s) >= 0);
+        assert_se(streq_ptr(s, "{\"b\":[\"foo\",\"bar\",\"baz\",\"qux\"],\"a\":\"<sensitive data>\",\"c\":-9223372036854775808,\"d\":\"-9223372036854775808\",\"e\":{}}"));
+        s = mfree(s);
         v = json_variant_unref(v);
 
         assert_se(json_build(&v, JSON_BUILD_OBJECT(
@@ -942,8 +944,9 @@ TEST(json_sensitive) {
                                              JSON_BUILD_PAIR("e", JSON_BUILD_EMPTY_OBJECT))) >= 0);
         json_variant_dump(v, JSON_FORMAT_COLOR|JSON_FORMAT_PRETTY, NULL, NULL);
 
-        assert_se(json_variant_format(v, JSON_FORMAT_REFUSE_SENSITIVE, &s) == -EPERM);
-        assert_se(!s);
+        assert_se(json_variant_format(v, JSON_FORMAT_CENSOR_SENSITIVE, &s) >= 0);
+        assert_se(streq_ptr(s, "{\"b\":[\"foo\",\"bar\",\"baz\",\"qux\"],\"c\":-9223372036854775808,\"a\":\"<sensitive data>\",\"d\":\"-9223372036854775808\",\"e\":{}}"));
+        s = mfree(s);
         v = json_variant_unref(v);
 
         assert_se(json_build(&v, JSON_BUILD_OBJECT(
@@ -954,8 +957,9 @@ TEST(json_sensitive) {
                                              JSON_BUILD_PAIR("e", JSON_BUILD_EMPTY_OBJECT))) >= 0);
         json_variant_dump(v, JSON_FORMAT_COLOR|JSON_FORMAT_PRETTY, NULL, NULL);
 
-        assert_se(json_variant_format(v, JSON_FORMAT_REFUSE_SENSITIVE, &s) == -EPERM);
-        assert_se(!s);
+        assert_se(json_variant_format(v, JSON_FORMAT_CENSOR_SENSITIVE, &s) >= 0);
+        assert_se(streq_ptr(s, "{\"b\":[\"foo\",\"bar\",\"baz\",\"qux\"],\"c\":-9223372036854775808,\"d\":\"-9223372036854775808\",\"a\":\"<sensitive data>\",\"e\":{}}"));
+        s = mfree(s);
         v = json_variant_unref(v);
 
         assert_se(json_build(&v, JSON_BUILD_OBJECT(
@@ -966,8 +970,8 @@ TEST(json_sensitive) {
                                              JSON_BUILD_PAIR_VARIANT("a", a))) >= 0);
         json_variant_dump(v, JSON_FORMAT_COLOR|JSON_FORMAT_PRETTY, NULL, NULL);
 
-        assert_se(json_variant_format(v, JSON_FORMAT_REFUSE_SENSITIVE, &s) == -EPERM);
-        assert_se(!s);
+        assert_se(json_variant_format(v, JSON_FORMAT_CENSOR_SENSITIVE, &s) >= 0);
+        assert_se(streq_ptr(s, "{\"b\":[\"foo\",\"bar\",\"baz\",\"qux\"],\"c\":-9223372036854775808,\"d\":\"-9223372036854775808\",\"e\":{},\"a\":\"<sensitive data>\"}"));
 }
 
 TEST(json_iovec) {